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Clinical Laboratory Sciences
Clinical Chemistry Review (carbohydrates, lipids, and proteins, Enzymes, nonprotein nitrogen compounds, bilirubin, Hormones, Electrolytes
Terms in this set (218)
Conversion of glucose to pyruvic acid or lactic acid
Production of glycogen from glucose
Production of glucose from glycogen
What is the end product of glycolysis?
What are the 2 most common methods for glucose determinations?
Glucose oxidase and hexokinase.
Glucose oxidase catalyzes the conversion of glucose to hydrogen peroxide and gluconic acid. The second step of the reaction is a peroxidase reaction, which is much less specific than the glucose oxidase reaction. Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate, which is then oxidized by G-6-PD in the presence ofNADP+. The hexokinase method is more accurate because it is subject to fewer interfering factors.
How is hypoglycemia diagnosed?
By the presence of Whipple's triad:
plasma glucose less than 40 mg/dL,
symptoms of hypoglycemia (nervousness, anxiety, neurologic abnormalities),
and relief of symptoms by administration of glucose.
What reagent is most commonly used to detect ketones in blood and urine?
Sodium nitroprusside reacts with acetoacetic
acid and to a lesser extent with acetone, but is insensitive to B-hydroxybutyric acid. A newer enzymatic method
uses the enzyme B-hydroxybutyrate dehydrogenase to detect B-hydroxybutyric acid and acetoacetic acid. This
method can be automated.
Describe the solubility properties of lipids.
Lipids are insoluble in water and soluble in organic solvents. In blood, lipids are soluble due to their combination with protein (lipoproteins).
What is the desirable level for HDL cholesterol?
What is the most concentrated solute in the blood?
Which element is found in protein but not in carbohydrates or lipids?
Nitrogen. The protein molecule is 16% nitrogen.
What is the most common method for measuring serum total protein?
The biuret method. Cuprous ions react with peptide bonds at an alkaline pH to produce a colored complex.
Why is the biuret method of protein analysis not suitable for urine or CSF protein?
It is not sensitive enough for the small amount of protein in the urine. Trichloracetic acid can be used to precipitate
protein in urine and CSF.
How would hemolysis affect the serum total protein level?
Hemoglobin in the serum would increase the protein level.
What clinical condition does low total protein cause?
Edema. Water leaves the blood vessels and goes into the tissues.
What is the main physiological function of albumin?
It maintains the osmotic pressure and the distribution of water in the body.
When albumin is low, edema results.
Albumin also has an important role in binding and transporting various substances in the blood, such as bilirubin and some drugs.
What are the most common dyes used for the direct analysis of albumin?
Bromcresol green (BCG) and bromcresol purple (BCP).
What happens to total protein and albumin levels in the nephrotic syndrome?
They decrease due to loss through the urine.
How is the concentration of globulins determined in a chemistry profile?
By subtracting albumin from total protein.
What is amphoterism?
The property of proteins to assume a positive, negative, or neutral charge depending on the pH of the medium.
With serum protein electrophoresis at pH 8.6, proteins carry a negative charge.
In the body, what charge do most proteins carry?
At pH 7.4 proteins are negatively charged (anions).
What support media are used for serum protein electrophoresis?
Cellulose acetate or agarose gel.
What is the significance of a sixth band migrating between beta and gamma on serum protein electrophoresis?
It means that the specimen was plasma, not serum.
The extra band is due to fibrinogen.
What stains are used in serum protein electrophoresis?
Coomassie brilliant blue (CBB), amido black, Ponceau S, and bromphenol blue.
CBB is more widely used because it is more sensitive.
What is the name of the instrument used to quantitate protein fractions following serum protein
In electrophoresis of serum at pH 8.6, which fraction is the fastest moving?
What causes increased albumin?
What causes decreased alpha-1 globulin?
Alpha-I antitrypsin deficiency.
This is seen with emphysema.
What causes a decreased gamma globulin fraction?
Describe the chronic response pattern.
Albumin is decreased and alpha-I, alpha-2, and gamma globulins are increased
Describe beta-gamma bridging
There is no valley between the beta and gamma globulin regions on SPE because of increased lgA.
Beta-gamma bridging is seen with cirrhosis.
Describe a polyclonal gammopathy.
There is a diffuse increase in the gamma region.
Describe the electrophoretic pattern seen in the nephrotic syndrome.
Albumin is decreased and alpha-2 is increased.
What is a monoclonal gammopathy?
A sharp peak in the gamma region due to an increase in one immunoglobulin. It is known as an "M spike" because of its association with malignancy, such as multiple myeloma and Waldenstrom's macroglobulinemia.
What is a paraprotein?
A monoclonal protein. lt can be either a complete immunoglobulin molecule or free light chains only.
What causes the hyperproteinemia seen in multiple myeloma?
An increase in one of the immunoglobulins or free light chains.
Which immunoglobulin is increased in Waldenstrom's macroglobulinemia?
This very high molecular weight protein causes the blood to have a high viscosity.
A patient has a monoclonal gammopathy on serum protein electrophoresis. What test can be done to determine which immunoglobulin is increased?
How are immunoglobulins quantitated?
Most often by immunoturbidimetry or immunonephelometry.
What must be done to the specimen prior to performing CSF or urine electrophoresis?
Urine and CSF must be concentrated because of their low protein content.
Which band is normal in urine electrophoresis?
Albumin. It is the smallest protein. A small amount crosses the glomerular membrane and is excreted in the urine.
A spike is observed in the gamma region on urine electrophoresis. What is present?
Bence Jones proteins. Bence Jones proteins are free immunoglobulin light chains (kappa or lambda) which are
present in serum and/or urine of patients with multiple myeloma. Immunofixation should be performed to
determine the specificity
What is the name of the test that detects oligoclooal CSF bands associated with multiple sclerosis?
High resolution electrophoresis (HRE). This technique uses higher voltage and a more concentrated buffer to separate proteins into as many as 12 bands
Which band is normally present in CSF electrophoresis but not in serum protein electrophoresis?
Prealbumin. It migrates ahead of albumin and accounts for approximately 4% of protein in the CSF.
What is the clinical significance of prealbumin?
It is an indicator of nutritional status and can be used to assess the adequacy of a nutritional feeding plan. Low levels are seen with protein malnutrition. This protein was originally named prealbumin because it migrates ahead
of albumin on high resolution electrophoresis. It has been renamed transthyretin.
What are cryoglobulins and when are they present?
Gamma globulins that precipitate in the cold. They may be present with multiple myeloma, Waldenstrom's
macroglobulinemia, leukemia, systemic lupus erythematosus, rheumatoid arthritis, and polycythernia.
What happens if the specimen for cryoglobulins is refrigerated?
The cryoglobulins precipitate out of the serum. A temperature of 37°C must be maintained during collection, processing, and storage
What is ceruloplasmin?
The primary copper-containing protein in plasma. Levels are usually decreased in Wilson's disease, an inherited
disorder of copper metabolism in which copper is deposited in the skin, corneas, liver, and brain. Levels increase in inflammation and malignancy because ceruloplasmin is an acute-phase reactant.. Measurement is usually by radial immunodiffusion (RID) or nephelometry.
What is an enzyme?
An organic catalyst. All enzymes are proteins. The substance upon which they act is called the substrate.
What is a coenzyme?
An organic cofactor required for an enzymatic reaction. Unlike the enzyme, which is not changed in the reaction, the coenzyme is changed.
Common coenzymes are NAD (nicotinamide adenine dinucleotide), NADH, NADP, and NADPH.
How is the change from NAD to NADH measured in automated analyzers?
By the change in absorbance at 340 nm. NADH absorbs light at 340 nm; NAD does not.
What are activators?
Inorganic cofactors such as Ca++ or Mg++- that are required for some enzyme reactions
What are isoenzymes?
Slightly different forms of an enzyme that catalyze the same reaction. Because of their different molecular structure, isoenzymes can be separated by their electrophoretic mobility, heat stability, or reaction with specific antibodies.
What are 2 ways in which enzymes are measured?
Traditionally, quantitation has been based on the activity of the enzyme on its substrate, either a decrease in the
concentration of the substrate, an increase in the concentration of the end-product, a decrease in the concentration of the coenzyme, or an increase in the concentration of the changed coenzyme.
Today, immunoassay methods are available to measure some enzymes by mass, for example, CK-MB.
What are zero-order kinetics?
When the rate of an enzyme reaction is dependent on the concentration of the enzyme only. This occurs when there
is an excess of substrate. In first-order kinetics, the rate of the reaction is proportional to the substrate concentration. Enzyme assays should be based on zero-order kinetics.
What is the clinical significance of an elevated lipase?
Lipase is increased in acute pancreatilis. It may also be significantly increased in many other conditions (e.g. opiate administration; pancreatic carcinoma; intestinal infarction, obstruction, or perforation; and pancreatic trauma).
What is the substrate for lipase?
Triglycerides. In turbidimetric assays, the rate of clearing of turbidity is related to the amount of lipase in the
What is the clinical significance of an elevated amylase?
Amylase is increased in acute pancreatitis. It may also be significantly increased in many other conditions, such as
opiate administration; pancreatic carcinoma; intestinal infarction, obstruction, or perforation; pancreatic trauma;
mumps; cholecystitis; hepatitis; cirrhosis; ruptured ectopic pregnancy; and macroamylasemia
What is the substrate for amylase?
Starch. It is broken down to sugars.
Why shouldn't EDTA plasma be used for an amylase determination?
Ca++ is needed for the reaction and EDTA chelates Ca++.
How do amylase and lipase values compare in acute pancreatitis?
They both begin to rise at roughly the same time after an attack (within 5-8 hours for amylase, 4-8 hours for lipase),
and both peak around 24 hours. Amylase returns to normal by 3-5 days; lipase remains elevated longer (8-14
Which enzyme is most specific for acute pancreatitis?
Lipase. It is not found is as many tissues.
Are amylase and lipase elevated in chronic pancreatitis?
They may be marginally elevated during attacks the early stages of the disease, but as the disease progresses severe destruction of acinar tissue eventually reduces the amount of enzymes released into the circulation. Then low levels may be seen.
Why might a pleural fluid amylase be ordered?
A normal pleural fluid amylase rules out acute pancreatitis.
What is the major diagnostic significance of elevated alkaline phosphatase (ALP)?
It is elevated with liver and bone disorders.
In which disease do the highest elevations of alkaline phosphatase (ALP) occur?
Paget's disease, a bone disease characterized by excessive bone destruction and unorganized bone repair. Values
10-25 times the upper reference limit are not unusual
When is a physiological increase in serum alkaline phosphatase seen?
During pregnancy due to release of ALP from the placenta and during childhood due to rapid bone growth.
Increased values at these times are expected and Explained by normal physiology. They are not indicative of
What is the clinical significance of acid phosphatase (ACP)?
The highest levels of ACP are in the prostate. At one time ACP was used to diagnose prostate cancer, but it has
been replaced by the more sensitive prostate specific antigen (PSA). ACP is rarely tested in serum today, but its
presence in vaginal washings may be significant in rape cases since it indicates the presence of semen. It can be
detected for up to 4 days after intercourse.
With which cl.inical condition are the highest levels of CK seen?
Duchenne's muscular dystrophy
What are some physiologic (nonpathologic) causes for increased total CK?
Intramuscular injections and vigorous exercise
Which cardiac enzyme is most specific?
CK-MB is the most specific cardiac enzyme, but not the most specific cardiac biomarker.
Cardiac troponins are more specific for acute myocardial infarction
Which cardiac biomarkers are currently used to diagnose acute myocardial infarction (AMI)?
Cardiac troponin (TnT or Tnl) and CK-MB, although CK-MB is playing a less important role since the introduction of troponin assays.
How is CK-MB measured?
Immunoassays using monoclonal antibodies have replaced electrophoresis. CK-MB is detectable 4-6 hours after chest pain due to AMI and remains elevated for 2-4 days.
Which cardiac marker is most specific for cardiac damage?
Cardiac troponins. Levels begin to rise within 3-12 hours of myocardial damage. TnT remains elevated for 8-21 days; Tnl for 7-14 days . Cardiac troponins are therefore useful both for early diagnosis and for late diagnosis after CK-MB has returned to normal.
How is cardiac troponin measured?
lmmunoassays using monoclonal antibodies.
Which cardiac marker is most likely to be elevated in a patient who is admitted to the hospital 4 days after a
suspected myocardial infarction?
Cardiac troponins. CK-MB would have returned to normal.
What is the clinical significance of B-type natriuretic peptide (BNP test)?
BNP is a cardiac hormone that is produced by the heart ventricles in response to ventricular volume expansion and pressure overload. It is a predictor of congestive heart failure in patients suffering from shortness of breath. BNP is also used to evaluate risk in patients who present with chest pain. High BNP predicts an increased risk of death or
subsequent heart attack in patients with acute coronary syndromes. The test is an immunoassay that can be
performed at point of care
What is the clinical significance of highly sensitive C-reactive protein (hs-CRP)?
CRP is a marker of inflammation and appears to be associated with increased risk for coronary heart disease,
sudden death, and peripheral artery disease. hsCRP is measured by turbidimetric immunoassays that use an
antibody to an epitope on the CRP molecule. These assays are sensitive to 0.01 mg/dL. hs-CRP should not be
confused with the conventional flocculation assays for CRP, which only detect gross elevations. At this time, hsCRP screening of the entire adult population is not recommended.
Which enzymes are most useful for the assessment of liver function?
Alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), Tglutamyltransferase (GGT), and lactate dehydrogenase (LD). Other liver function tests include total protein,
albumin, and total and conjugated (direct) bilirubin.
Which enzyme is most sensitive for all types of liver disease?
GGT. It is elevated in most cases of liver disease, regardless of cause. Levels are highest with biliary obstruction.
Is AST or ALT more specific for liver disease?
ALT. AST is found in equal amounts in heart, skeletal muscle, and liver
What are the substrates for AST?
What are the substrates for ALT?
Which disease state bas the highest elevation of AST and ALT?
Where is LD found?
In all cells of the body. Because of its wide distribution, serum LD elevations occur in a variety of clinical
conditions including myocardial infarction, hemolysis, and disorders of the liver, kidneys, lung, and muscle. In
liver disease, LD does not increase as much as AST and ALT.
What effect does hemolysis have on LD?
It is increased because LD is I 00-150 times more concentrated in the RBCs.
How should specimens for LD be stored and why?
They should be stored at 25°C and analyzed within 48 hours. They should not be refrigerated because LD decreases more rapidly at 4°C than at 25°C.
Which clinical condition results in the highest levels of LD?
Which enzyme is a sensitive indicator of alcoholism?
Which enzyme would be helpful in establishing a diagnosis of bone disease?
Which enzymes would be helpful in establishing a diagnosis of muscle disorders
CK, AST, LD, and aldolase.
What is the clinical significance of a deficiency of glucose-6-phospbate dehydrogenase (G-6-PD)?
Inherited deficiencies ofG-6-PD can lead to hemolytic anemia following exposure to certain drugs. G-6-PD is in the RBCs, so the specimen required is whole blood.
What is the clinical significance of low pseudocholinesterase levels?
Low levels are seen following exposure to insecticides and nerve gases and in patients with hypersensitivity to the muscle relaxant succinylcholine.
What is the advantage to using enzymes as reagents?
Enzymatic assays are very specific. There are fewer false positives than with colorimetric assays.
Name 3 substances that are elevated in the blood with renal disease.
BUN (blood urea nitrogen), creatinine, and uric acid.
What is urea?
The end product of protein metabolism. It is synthesized in the liver from ammonia and carbon dioxide.
What does azotemia mean?
An elevated level of urea in the blood.
What is the most common method for measuring BUN?
Enzymatic, using the enzyme urease to hydrolyze urea. The resulting ammonium ion is measured.
Why should tubes containing fluoride or citrate not be used when collecting blood for urea if analysis will be
by the urease method?
Fluoride and citrate inhibit urease.
Where is 98% of the body's creatine located?
What is creatinine?
The anhydride of creatine. Creatinine is formed from creatine by splitting out of water.
What reaction is used to measure creatinine?
The Jaffe reaction using alkaline picrate. It is a nonspecific but still clinically useful method.
What is the significance of the BUN:creatinine (BUN:CR) ratio?
It can be used to differentiate between the three types of azoternia: prerenal, renal, and postrenal.
What is the least variable nitrogenous constituent of blood?
Creatinine, because it is related to muscle mass and is not affected by diet.
What is uric acid?
The end product of purine metabolism. The purines are adenosine and guanine, components of nucleic acids. Uric
acid is increased with gout, renal disease, and conditions where there is high cellular turnover, such as leukemia.
What reagent is commonly used to measure uric acid?
The preservative sodium fluoride must not be used to collect the blood sample because it destroys uricase.
Why must the pH of urine for a uric acid determination be adjusted to 7.5-8?
To prevent precipitation of uric acid. Uric acid precipitates at acid pH.
Where is ammonia formed?
Mainly in the intestines from deamination of amino acids. It is converted to urea by the liver.
When is ammonia elevated?
With hepatic failure and Reye's syndrome. High levels are neurotoxic.
What is Reye's syndrome?
An acute, often fatal encephalopathy and fatty degeneration of the liver, seen primarily in children. It is associated with the use of aspirin in children with viral infections
Which amino acid is increased in the blood of patients with phenylketonuria (PKU)?
Phenylalanine. PKU is due to a deficiency of the enzyme phenylalanine hydroxy lase which catalyzes the
conversion of phenylalanine to tyrosine. If untreated, PKU leads to mental retardation. The traditional method to
test for PKU, the Guthrie bacterial inhibition assay, is being replaced by tandem mass spectrometry (MS/MS),
which can detect more than 25 genetic disorders in a single blood specimen. All states screen newborns for PKU.
What may result if blood for PKU is drawn before 24 hours of age?
Which amino acids are increased in maple syrup urine disease (MSUD)?
Leucine, isoleucine, and valine. The urine bas a burnt sugar odor. MSUD leads to mental retardation and
sometimes death. A modified Guthrie test or MS/MS are used for diagnosis. MSUD can be treated by dietary
modification if diagnosed early. Some states include MSUD in their newborn screening panel.
What is bilirubin?
The degradation product of heme. It is produced in the reticuloendothelial cells following breakdown ofRBCs.
Which protein transports bilirubin in the blood?
Name the 3 types of bilirubin
Unconjugated, congugated, and delta.
Together these fractions make total bilirubin. Unconjugated (indirect) bilirubin is bilirubin en route to the liver. Once it goes through the liver it is known as conjugated (direct) bilirubin or bilirubin diglucuronide.
Delta bilirubin is covalently bound to albumin and is only present with hepatic obstruction. It reacts as conjugated bilirubin in most methods.
What happens to bilirubin in the liver?
It is conjugated with glucuronic acid by the enzyme uridyldiphosphate glucuronyl transferase (UDPG-T).
Following conjugation, it is excreted into the intestine via the bile duct and is reduced by bacteria to urobilinogen.
Urobilinogen is oxidized to urobilin, which gives stools their normal color.
What is the significance of clay-colored or light stools?
It is a sign of obstruction of the bile duct. Urobilin is not being produced because bilirubin is not reaching the
Which substances related to bilirubin metabolism are normally found in the urine?
Only urobilinogen. Bilirubin should not be present in urine.
What urine chemistry abnormality is seen with complete obstruction of the biliary tract?
Which bilirubin fractions are analyzed in the laboratory?
Total and conjugated (direct). The unconjugated (indirect) level is calculated by subtracting conjugated from total.
Compare the solubility of conjugated and unconjugted bilirubin.
Conjugated bilirubin is soluble in water; uncongugated bilirubin is not. Both are soluble in alcohol.
Which form of bilirubin can be excreted in the urine?
Only conjugated bilirubin. It is not bound to protein, whereas uncongugated bilirubin is bound to albumin and is too large to be filtered through the glomeruli.
What methods are used for determination of billrubin levels?
Malloy-Evelyn and Jendrassik-Grof. Both use a diazo reagent to react with bilirubin and produce colored
azobilirubin. The Malloy-Evelyn procedure is carried out at at an acid pH; Jendrassik-Grof at an alkaline pH.
Conjugated bilirubin reacts without an accelerator (therefore called direct bilirubin); unconjugated bilirubin
requires the addition of an accelerator (therefore called indirect bilirubin). The Jendrassik-Grof method has some
advantages over the Malloy-Evelyn method. Both have been automated.
Name the accelerators for the Malloy-Evelyn and Jendrassik-Grof methods.
How do normal values for billrubin in a newborn compare to those in an adult?
Levels are higher in the newborn. The total bilirubin in a 3- 5 day old full-term infant is 4-6 mg/dL; for a premature
infant, 10-12 mg/dL.
What would cause an increase in total bilirubin with a normal concentration of conjugated bilirubio?
Prehepatic jaundice, for example, hemolytic transfusion reaction, hemolytic anemia, or hemolytic disease of the fetus and newborn.
What causes physiologic j auodice of the newborn?
Bilirubin metabolism is impaired because the newbom's immature liver does not produce the enzyme required for
bilirubin conjugation. Bilirubin may remain elevated for up to 2 weeks. Phototherapy is used to reduce the level of
bilirubin when necessary.
lo hemolytic disease of the newborn, which bilirubio fraction is elevated and why?
Uncongugated, due to excessive breakdown ofRBCs by maternal antibody.
What is the risk to the newborn from a high level of uncongugated bilirubin?
Unconjugated bilirubin (indirect) has a high affinity for brain tissue and causes necrosis (kemicterus). Without
appropriate treatment, mental retardation, hearing deficits, or cerebral palsy may result.
Name 2 conditions in which congugated bilirubin is elevated.
Hepatic and posthepatic jaundice.
What are the typical lab findings in posthepatic jaundice?
Increased total bilirubin, increased congugated bilirubin, decreased urine urobilinogen, and clay-colored stools.
Which disorder results in the highest levels of conjugated bilirubin?
Obstructive liver disease.
What are tropic hormones?
Hormones produced by one endocrine gland that regulate another endocrine gland. For example, the hypothalamus secretes tropic hormones that stimulate the anterior pituitary. The anterior pituitary produces thyroid stimulating hormone (TSH), which stimulates the thyroid gland, and adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex.
What type of method is used for most hormone assays?
What is the precursor in the biosynthesis of all steroid hormones?
What are some examples of steroid hormones?
Cortisol, aldosterone, estrogen, testosterone, progesterone.
Where is follicle-stimulating hormone (FSH) produced and what is its main action?
It is produced in the anterior pituitary. It stimulates production of sperm and eggs. There is a sharp increase in FSH just before ovulation.
Where is growth hormone (GH) produced and what is its main action?
It is produced in the anterior pituitary. It stimulates protein synthesis and cell growth and division.
Where is thyroid-stimulating hormone (TSH) produced and what is its main action?
It is produced in the anterior pituitary. It stimulates the thyroid to produce T3 and T4. It is also known as
Where is adrenocorticotropic hormone (ACTH) produced and what is its main action?
It is produced in the anterior pituitary. It stimulates the adrenal cortex to produce corticosteroids. ACTH exhibits diurnal variation, with highest levels in the early morning and lowest levels late in the day
Where is anti-diuretic hormone (ADH) produced and what is its main action?
It is produced in the hypothalamus and stored in the posterior pituitary. It regulates reabsorption of water from the distal convoluted tubules. ADH is decreased in diabetes insipidus, leading to the excretion of an increased volume of dilute urine
Where is cortisol produced and what is its main action?
It is produced in the adrenal cortex and regulates carbohydrate, fat, and protein metabolism, water and electrolyte balance, and suppresses inflammatory and allergic reactions.
What is Addison disease?
Adrenal insufficiency, characterized by decreased cortisol and increased ACTH. (This is an example of feedback
control. The ACTH is increased because of the decreased cortisol; however in Addison disease, the adrenal gland is
unable to respond appropriately to the ACTH.)
What is Cushing syndrome?
The signs and symptoms associated with elevated cortisol levels. Cushing syndrome may be due to tumors of the
pituitary (Cushing disease), tumors of the adrenal glands, ectopic ACTH-secreting tumors, or administration of
glucocorticoids or ACTH.
What is the advantage of a 24-hour urine free cortisol measurement?
It is not affected by circadian variation and is the most sensitive and specific screen for excess cortisol production. It is measured by tandem mass spectroscopy.
Where is aldosterone produced and what is its main action?
It is produced in the adrenal cortex. It increases retention of Na+ and excretion of K+ and H+
What are catecholamines?
The hormones secreted by the adrenal medulla: epinephrine, norepinephrine, and dopamine. Their metabolite is vanillylmandelic acid (VMA).
Where is progesterone produced and what is its main action?
It is produced in the ovaries. It prepares the uterus for pregnancy and stimulates lactation.
What is the major estrogen produced by the ovaries?
Estradiol (E2). Estrogens are involved in the development of the female reproductive organs and secondary sex
characteristics, regulation of the menstrual cycle, and maintenance of pregnancy
Which hormones are used to assess fetal well·being?
Estriol, progesterone, and its metabolite, pregnanediol.
Which hormone can be measured by a home testing kit to determine the time of ovulation?
Luteinizing hormone (LH), secreted by the anterior pituitary. There is a sharp peak just before ovulation.
Why are estrogen and progesterone receptor assays performed?
To establish a prognosis for patients with breast cancer.
Where is thyroxine (T4) produced and what is its main action?
It is produced in the thyroid and controls metabolic rate, growth and development, and sexual maturation.
Triiodothyronine (T3) is formed primarily from deiodination of T4 by tissues.
Which is the physiologically active form of T4?
Free T4 (FT4). Most T4 is bound to thyroxine binding globulin (TBG), the main carrier protein for T4 and T3.
What is the recommended screening test for thyroid function?
Thyroid·stimulating hormone (TSH). With primary hypothyroidism, TSH may be increased before clinical
symptoms. A normal TSH usually excludes a diagnosis of primary thyroid dysfunction.
What further thyroid testing is recommended when the TSH is abnormal?
Free T4. Free T3 assays are available but are not routinely performed.
What methodology is most often used to measure TSH and free T4?
A patient has a high TSH and a low free T4. What is a likely diagnosis?
Primary hypothyroidism, a disorder of the thyroid gland. TSH increases as the pituitary tries to stimulate the
thyroid to produce more T3 and T4.
A patient bas a low free T4 and a low TSH. What is a likely diagnosis?
Secondary hypothyroidism, a pituitary disorder. The thyroid is nonnal, but it isn't stimulated to produce the nonnal amount of thyroid hormones because of insufficient TSH from the pituitary.
How can primary hypothyroidism be differentiated from secondary hypothyroidism?
By TSH. Primary hypothyroidism is a disorder of the thyroid gland. TSH increases as the pituitary tries to stimulate the thyroid to produce more T3 and T4. Secondary hypothyroidism is a pituitary disorder. TSH levels are low.
What lab findings are typical of primary hypothyroidism?
High TSH and low free T4.
What screening is done for neonatal hypothyroidism?
Measurement ofT4 or TSH or a combination of tests is performed using dry blood spots or cord blood. All 50
states require newborn screening for hypothyroidism to eliminate severe mental retardation associated with thyroid hormone deficiency.
What lab findings are typical of hyperthyroidism?
TSH is low and free T4 is high. The high level of T4 produced by the thyroid sends a feedback message to the pituitary to slow down production of TSH.
What is Graves' disease
An autoimmune disease that is the most common type of hyperthyroidism in the U.S. Thyroid stimulating hormone
receptor antibodies (TRab) are present in the serum.
What is Hasbimoto's thyroiditis
A type of autoimmune hypothyroidism and the most common cause of hypothyroidism in the developed world. It is characterized by the presence of anti-thyroid antibodies that gradually impair thyroid function, leading to decreased synthesis of thyroid hormones. The best test for diagnosing the condition is thyroid peroxidase antibody (TPOAb), which is present in 80-99% of cases. Hashimoto's is also known as chronic lymphocytic thyroiditis.
Where is parathyroid hormone (PTH) produced and what is its main action?
It is produced in the parathyroid glands. It increases serum calcium and decreases phosphates. PTH is increased in primary hypcrparathyroidism and decreased in hypoparathyroidism
Where is glucagon produced and what is its main action?
It is produced in the alpha cells of the pancreas. It increases glucose levels.
What are electrolytes?
Substances that carry an electric current when dissolved in water. Anions are negatively charged and cations are
What are the major electrolytes?
Sodium, potassium, chloride, and bicarbonate
What is the major extracellular cation?
What is the major intracellular cation?
What is the major intracellular anion?
What is the major extracellular anion?
Which hormone regulates the concentration of sodium?
Why should standards for sodium be stored in plastic containers instead of glass?
Sodium can leech from glass containers and cause falsely elevated values.
How are sodium and potassium usually measured?
By ion selective electrodes (ISE).
What is the approximate ratio of potassium between RBCs and serum?
20: 1. This explains why hemolysis must be avoided when measuring potassium.
What are several factors that can cause artifactual (false) elevations of potassium?
Fist clenching, prolonged tourniquet time, contamination with K2EDTA or IV fluid, hemolysis, thrombocytosis,
Why is potassium slightly higher in serum than in plasma?
Because potassium is released from platelets during clotting.
Before reporting an elevated potassium, what should be checked?
The specimen should be checked for hemolysis or excessive delay in separating the serum/plasma from the RBCs. Either could be responsible for a false elevation.
What clinical condition results from very high or very low potassium levels?
What is chloride's role in the body?
It maintains hydration, osmotic pressure, and electrolyte balance.
What is pilocarpine?
A topical drug used in the sweat test to stimulate sweat glands.
In iontophoresis, an electric current delivers
pilocarpine nitrate to the sweat glands on the forarm or thigh. Sweat is collected and chloride is measured. A source of error is failure to collect an adequate volume of sweat. The sweat test should be performed at a CF Foundation accredited care center.
What happens to CO2 if the sample is exposed to air?
What does anion gap measure?
Unmeasured anions. The anion gap is increased with renal failure, diabetic acidosis, lactic acidosis, and the presence of drugs or toxins.
What is the most abundant mineral. in the body?
Which anticoagulants cause a false decrease in calcium?
EDTA, citrate, and oxalate. All prevent coagulation by binding Ca* . Heparin is the only acceptable anticoagulant
for calcium determinations.
Which form of calcium is physiologically active?
Why is pH an important consideration in ionized calcium determinations?
As pH decreases (acidosis), calcium dissociates from its complexed forms, increasing the amount of free ionized
calcium in the serum
What is the commonly used method for total calcium?
A dye-binding reaction with ortho-cresolphthalein complexone (CPC) or arsenazo III. Atomic absorption is the
reference method but rarely used in clinical labs.
How is ionized calcium measured?
By ion selective electrodes.
What substances regulate calcium levels?
PTH, calcitonin, and vitamin D.
What is tetany?
Muscle spasms, cramps, and irritability due to decreased calcium or magnesiu
What is the most common cause of hypercalcemia?
How does hyperparathyroidism affect the level of serum phosphorus?
Phosphorus is decreased.
What happens to calcium when phosphorus is increased?
It decreases. There is a reciprocal relationship between calcium and phosphorus.
A hospitalized patient exhibits signs of tetany but her ionized calcium is normal. What other analyte should
Magnesium. Low levels of magnesium also cause tetany.
How does the reference range for phosphorus in growing children compare to that of adults?
It is higher in children.
What must be done to urine prior to performing a urine phosphorus analysis?
It must be acidified to pH 6 to prevent precipitation of phosphates.
How does hemolysis affect iron level?
Because of the high concentration of iron in hemoglobin, even minimal hemolysis will give falsely elevated results.
To minimize this effect, serum/plasma should be separated from RBCs within one hour of collection and even slightly hemolyzed specimens should not be analyzed.
How are iron levels affected by the time of day when the specimen is drawn?
Iron shows a marked diurnal variation. Levels are approximately 30% higher in the morning.
Which protein transports iron?
Transferrin. It is normally 20-55% saturated with iron.
Where is most of the iron in the body?
Name 2 storage forms of iron.
Ferritin is the primary storage form. It is present in most cells and is a readily mobilized form of storage iron. A
small amount of iron is also stored as hemosiderin
How are the iron and total iron binding capacity (TIBC) affected in iron deficiency anemia?
Serum iron is decreased and TIBC is increased. TIBC is an indirect measurement of transferrin. TIBC is
infrequently performed since the development of improved transferrin assays.
What is the most sensitive test for detection of iron deficiency anemia?
Serum ferritin. A decreased serum ferritin is almost always indicative of iron deficiency anemia.
What is hereditary hemochromatosis and what tests are used for diagnosis?
Hereditary hemochromatosis is the most common of the iron overload diseases. It causes the body to absorb and
store too much iron. The iron panel consists of serum iron (SI), ferritin, total iron binding capacity (TIBC) and
transferrin saturation (TS, also known as percent saturation). TS determines how much iron is bound to transferrin, the protein that carries iron in the blood. After a 12-hour fast, the TIBC and SI are measured and the TS is
calculated (Sl/TIBC = TS). The serum ferritin test shows the level of iron in the liver.
What test results are typical in hereditary hemochromatosis?
Serum iron, ferritin, and transferrin saturation are all increased. Total iron binding capacity is decreased.
What is lactate?
Lactic acid, an intermediary in carbohydrate metabolism. There are 2 types of lactic acidosis:
• Hypoxic, due to decreased oxygen delivery to the tissues
• Metabolic, associated with disease, drugs/toxins, and inborn errors of metabolism
The mortality rate for lactic acidosis is greater than 60%.
Name a reagent used to measure lactate.
Lactate dehydrogenase (LD). Lactate is oxidized to pyruvate by LD in the presence ofNAD+. The NADH formed is measured at 340 nm.
What happens to lactate in the blood following collection?
It increases due to glycolysis.
What is a colligative property?
One that depends on the number of solute particles, regardless of size or molecular weight. The colligative
properties are osmotic pressure, vapor pressure, boiling point, and freezing point.
How is osmolality usually measured in the clinical lab?
By freezing point depression.
What does the urine to serum osmolality ratio indicate?
The degree to which the kidneys concentrate the glomerular filtrate. The normal urine:serum ratio is
1:1- 3: 1.
Which substance contributes most to serum osmolality?
Sodium accounts for almost half.
What are several clinical conditions that result in an increased serum osmolality?
Dehydration, uremia, diabetes mellitus, alcohol intoxication, salicylate intoxication, and excessive electrolyte IVs.
What is osmolal gap?
The difference between measured osmolality and calculated osmolality. It is used to diagnose poisonings and to estimate blood alcohol levels. The reference range is 0-10 mOsm/kg. Higher levels indicate an abnormal
concentration of an unmeasured substance such as isopropanol, methanol, ethylene glycol, or acetone.
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