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Clinical Chemistry Review (carbohydrates, lipids, and proteins)

Terms in this set (86)

Define glycolysis
Conversion of glucose to pyruvic acid or lactic acid
Define glycogenesis
Production of glycogen from glucose
Define Glycogenolysis
Production of glucose from glycogen
What is the end product of glycolysis?
lactic acid
What is the reference range for a fasting glucose in an adult?
70 - 99 mg/dL
Compare the normal blood glucose level for newborns and adults.
Glucose is lower in the newborn. The condition is known as physiologic hypoglycemia.
How do glucose levels differ in venous and capillary specimens?
Following ingestion of sugar, glucose levels are a little higher in capillary blood. In a fasting specimen, values are
the same.
What are critical values for glucose?
Each laboratory establishes its own critical levels, but< 40 mg/dL and> 600 mg/dL are often used.
What is glucosuria?
Glucose in the urine. Glycosuria is a more general term, referring to the presence of any sugar in the urine.
What is renal threshold?
The blood concentration of a substance that can be reabsorbed by the renal tubules. For glucose, the average renal threshold is 160-180 mg/dL. When the blood level exceeds this amount, glucose is excreted in the urine.
What is hyperglycemia?
High blood sugar. It is most often due to diabetes mellitus.
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 happens when glucose levels drop too low?
Central nervous system dysfunction.
When are ketones present in the blood?
Whenever there is impaired carbohydrate metabolism with breakdown of fatty acids, such as uncontrolled diabetes mellitus, starvation, vomiting, or low carbohydrate diet.

The ketones are acetone, acetoacetic acid, and B-hydroxybutyric acid

High levels lead to metabolic acidosis (ketoacidosis)
What reagent is most commonly used to detect ketones in blood and urine?
sodium nitroprusside

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 main form of lipid storage in the body?
Triglycerides in adipose tissue.
Name 2 substances that play a role in the digestion of lipids.
lipase and bile salts
Why is it recommended that a patient be seated for 5 minutes prior to drawing blood for cholesterol?
Values are higher when standing.
What is the major site of cholesterol synthesis?
The liver.
Which lipoprotein transports most cholesterol?
Low density lipoprotein (LDL) transports approximately 70% of the body's cholesterol. LDL transports cholesterol to blood vessels and other tissues where it is deposited
What specimen is required for total cholesterol?
Serum is the sample of choice. Samples do not have to be fasting unless triglycerides or LDL cholesterol will also
be measured on the same specimen.
What is the most common method for cholesterol determination?
Enzymatic using cholesterol esterase and cholesterol oxidase.
How is HDL cholesterol measured?
Basically the same way as total cholesterol except that lipoproteins other than HDL are first removed by precipitation or blocked from reacting by addition of other reagents ( direct method).

Direct methods are most often used since they don't require a pre-treatment step and are readily automated.
What is the desirable level for HDL cholesterol?
>40 mg/dL.
Which lipid is the major component of atherosclerotic plaques in arteries?
LDL-cholesterol. Reduction of LDL-cholesterol has become the main goal of cholesterol-lowering therapy.
How is LDL cholesterol determined?
It can be calculated by the Friedewald fonnula: LDL cholesterol = Total cholesterol - HDL cholesterol -
(Triglycerides/5). Triglycerides divided by 5 is an estimate of VLDL cholesterol.

The formula is not valid if triglycerides are greater than 400 mg/dL. The disadvantage to the calculated LDL cholesterol is that it is dependent on the accuracy of 3 other determinations. Several methods for direct measurement of LDL cholesterol are now available and are recommended for improved precision and accuracy.
What is the structure of triglyceride?
Triglyceride is made of one molecule of glycerol and 3 molecules of fatty acid.
What are exogenous triglycerides?
Triglycerides from the diet.

They are carried by the chylomicrons. Endogenous triglycerides are synthesized in the body.
What is usually measured in triglyceride assays?
Glycerol, following cleavage of fatty acids by lipases and proteases.
What are chylomicrons?
They transport exogenous triglycerides and account for the turbidity of serum following a meal.

The largest and least dense of the lipoproteins.
What tests should be included in a lipoprotein panel?
Total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides.
What patient preparation is required for a lipoprotein profile?
The patient should be in metabolic steady state and should maintain usual diet and weight for 2 weeks prior to
blood collection. The patient should not exercise vigorously for 24 hours before the blood is drawn. The patient should be fasting and should remain seated for 5 minutes before the blood is drawn.
A non-fasting specimen is received for a llpoprotein panel. Which results, is any, will be useful?
Only total cholesterol and HDL cholesterol. If the total cholesterol is 200 mg/dL or higher or the HDL cholesterol
is less than 40 mg/dL, the tests should be repeated on a fasting specimen.
What is the significance of turbid or lipemic serum?
It is indicative of increased chylornicrons and/or VLDL, both of which contai n large amounts of triglycerides.
What causes a "cream layer" on top of plasma after overnight refrigeration?
High levels of triglycerides or chylomicrons.
What might lead you to suspect that a specimen is non-fasting?
Lipemia
A specimen for a lipid profile had elevated triglycerides but normal total cholesterol. What is the most likely
cause?
A non-fasting specimen. Recent ingestion of fats will elevate triglycerides but not total cholesterol. The tests should be repeated on a fasting specimen.
What is metabolic syndrome?
A group of risk factors for development of atherosclerotic cardiovascular disease and type 2 diabetes. They include low HDL-C, high LDL-C, high triglycerides, high blood glucose, high blood pressure, and abdominal obesity.
What is the most concentrated solute in the blood?
Protein
The reference range is 6.4-8.3 g/dL
Most other chemistry analytes are measured in mg/dL
Which element is found in protein but not in carbohydrates or lipids?
Nitrogen. The protein molecule is 16% nitrogen.
Where are most proteins synthesized?
In the liver.
What is the major waste product of protein catabolism?
Urea. It is excreted in the urine.
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 the normal A:G ratio?
1- 1.8.
A reversed A:G ratio is seen with monoclonal gammopathies and other increases in the globulin fraction.
Calculate the A:G ratio for a patient whose total protein is 9.2 g/dL and whose albumin is 4.2 g/dL.
0.84.

Globulins are determined by subtracting albumin from total protein (9.2-4.2 g/dL = 5.0).

A:G ratio is determined by dividing albumin by globulin (4.2 / 5.0 = 0.84).

This patient has a reversed ratio, indicating increased globulins possibly due to a gammopathy
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 is the principle of serum protein electrophoresis (SPE)?
When an electric current is applied to a medium containing charged particles, the particles will migrate to the pole of the opposite charge.

Negatively charged particles (anions) will migrate toward the positively charged pole (anode) and positively charged particles (cations) will migrate toward the negatively charged pole (cathode).

The rate of migration depends on the net charge of the particle, the size and shape of the molecule, the strength of the electric field, the properties of the support medium, and the temperature.
What support media are used for serum protein electrophoresis?
Cellulose acetate or agarose gel.
What is electroendosmosis?
The flow of buffer toward the cathode due to the negative surface charge present on the support medium. On
cellulose acetate, this results in gamma globulins being swept toward the cathode
What is the order of migration of serum proteins to the anode on cellulose acetate at pH 8.6?
At pH 8.6, proteins are negatively charged and migrate toward the anode in the following order:
albumin,
alpha-I globulin,
alpha-2 globulin,
beta globulin, and
gamma globulin.
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
electrophoresis
A densitometer.
In electrophoresis of serum at pH 8.6, which fraction is the fastest moving?
albumin
What causes increased albumin?
dehydration
What causes decreased alpha-1 globulin?
Alpha-I antitrypsin deficiency.
This is seen with emphysema.
What causes a decreased gamma globulin fraction?
Hypogammaglobulinemia.
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. The name should not be misinterpreted to mean that the increased immunoglobulin is IgM. It could be lgM, but more commonly is lgG or IgA.
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?
IgM.

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?
Immunofixation.
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.
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