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Clinical chemistry chapter 12

Terms in this set (56)

Which of the following is not an NPN substance?
allantoin
ammonia
creatinine
urea
allantoin
Which compound constitutes nearly half of the NPN substance in the blood?
ammonia
creatine
urea
uric acid
urea
An uria N result of 9 mg/dl is obtained by a tech. What is the urea concentration?
19.3
Urea concentration= urea N * 2.14
prerenal azotemia is caused by
congestive heart failure
a tech obtains a urea N of 61 mg/dl and a serum value of 2.5 mg/dl on a patient. These results indicate?
Urinary tract obstruction
Uric acid is the final product of
Purine metabolism
Which one of the listed conditions is not associated with elevated plasma uric acid concentration?
Allopurinol over treatment
Gout
Lesch-Neyhan syndrome
Renal disease
Allopurinol over treatment
In the Jaffe reaction, a red-orange chromogen is formed when creatinine reacts with
Picric acid
Substances known to increase results when measuring creatinine by the Jaffe reaction include all of the following except
ascorbic acid
bilirubin
glucose
alpha- keto acids
bilirubin
Ammonia concentrations are usually measured to evaluate
hepatic encephalopathy
A complete deficency of hypoanthine guanine phosphoribosyltransferase results in which disease?
Lesch-Nyhan syndome
when calculating creatinine clearance using the MDRD equation, which of the following factors are considered?
Verification that the person has been fasting
identification of ethnicity
body mass
time of day of blood collection
physical workout schedule of the patient
identification of ethnicity
true or false? Serum creatinine levels may be falsely elevated when the patient is taking cephalosporin.
True
When measuring ammonia blood levels, which of the following might cause a false increase in this analyte?
The patient had 2 cigarettes 15 minutes prior to blood draw
the patient was fasting for hours prior to blood collection
immediately after phelbotomy, the blood sample was maintained on ice
the patient had a steak dinner the night before
none of the above
The patient had 2 cigarettes 15 minutes prior to blood draw
NPN compounds
-traditionally used to monitor renal function
-concentration of nitrogen -containing compounds was quantified spectrophotometrically by converting nitrogen to ammonia
-subsequent reaction with Nessler's reagent produces a yellow color
-NPN fraction comprises 15 compounds of clinical intrest
Urea
-an NPN compound present in highest concentration in blood
-nitrogen is released as a result of protein metabolism, converted to urea, and excreted as a waste product
- liver--> blood --> kidney--> out (mostly urine)
BUN
blood urea nitrogen
Clinical application of urea
used to evaluate renal function
-hydration
-nitrogen balance
-adequacy of dialysis
-aiding in the diagnosis of renal disease
Method for urea
Enzymatic (urease)-most common
Specimen requirements for Urea
plasma
serum
urine
interfering substance in testing for urea
in plasma, avoid ammonium ions and high citrate and fluoride
susceptible to bacterial decomposition
Enzyme for urea
urease
BUN reference ranges
in plasma or serum- 6-20mg/dl (2.1 -7.1 mmol urea/day)
in urine,24 hour-12-20 g/day (.43-.71 mol urea/ day)
What is indicated by a low BUN?
low protein intake
severe liver disease
Normal BUN/creatinine ratio
10:1-20:1
Azotemia
elevated concentration of urea in blood
Uremia
very high plasma urea concentration with renal failure
Prerenal azotemia
reduced renal blood flow
Renal azotemia
decreased renal function(renal function)
Postrenal azotemia
obstruction of urine flow
Uric acid
- product of catabolism of purine nucleic acids
- most is reabsorbed and reused
-purines are converted to uric acid in liver
in plasma form liver --> kidney where it is filtered by glomerulus
-70% is eliminated by renal excreation
Clinical application of Uric acid
- assessment of inherited disorders of purine metabolism
-confirmation of diagnosis and monitoring of treatment of gout
- assistance in diagnosis of renal calculi
-detection of kidney dysfunction
Most common testing method for uric acid
Uricase
Specimen requirement for Uric acid
- heparinized plasma, serum, or urine
- remove serum from cell quickly
- diet may affect
Reference interval for Uric acid
Adults:
plama/serum- M 3.5-7.2 mg/dL; F 2.6-6.0 mg/dL
urine, 24 hour- 250-750 mg/day
Child:
plasma/serum- 2.0-5.5 mg/dL
Hematuricemia
elevated levels of uric acid
Hematuricemia is found in
- inherited disorders of purine metabolism
- gout
- increased catabolism of nucleic acid
- increased metabolism of cell nuclei
- chronic renal disease
- hemolytic or megaloblastic anemia
Hypouricemia
decreased levels in uric acid
Hypouricemia is found in
- liver disease
- defective tubular resorption
- chemotherapy
Creatinine/ Creatine
- is formed from creatine, creatine phosphate in muscle, is excreted in plasma at rate related to muscle mass
- plasma creatinine is inversly related to GFR
- formed mostly in liver
Clinical application in Creatinine/creatine
- used to determine sufficiency of kidney function
- severity of kidney damage
- monitor progression of kidney disease
Creatinine clearance
measure amount of creatinine eliminated from blood to kidneys
Glomerular filtration rate (GFR)
volume of plasma filtered by glomerulus per unit of time
Abbreviated Modification of diet in renal disease (MDRD) equation
include 4 variables:
serum creatinine concentration
age
gender
ethnicity
Jaffe reaction
creatine reacts with piric acid in alkaline solution to form red-orange chromogen
this test is time-consuming and not automated
Kinetic Jaffe reaction
Serum is mixed with alkaline picrate and rate of change in absorbance is measured
this test is rapid and inexpensive and easy
What is the reference method for Creatinine/creatine?
Isotope dilution mass spectrometry
Specimen requirements for Creatinine/creatine
-plasma
-serum
-urine
- hemolysed samples should be avoided
-may be refigerated for 4 days
Sources of error for creatinine/creatine
-ascorbate
-glucose
-alpha-keto acids
-uric acid
-blirubin- negative bias
-patient use of cephalosporin, dopamine, lidocaine
Reference intervals for Creatinine/creatine
Adult:
plasm or serum- M Jaffe .9-1.3 enzymatic method .6-1.1; F Jaffe 0.6-1.1 enzymatic method .5-.8
urine, 24 hour- M 800-2000 F 600-1800
Child:
Plasma- jaffe .3-.7 enzymatic method 0.0-.6
Creatinine
when plasma creatinine is elevated, GFR is decreased, this indicates renal damage
Creatine
elevated concentration associated with muscle disease:
MD
poliomyelitis
hyperthyroidism
trauma
not elevated in renal disease
Ammonia
formed in deamination of AA during protein metabolism
removed from circulation
converted to urea in liver
toxic when free
Clinical application of Ammonia
-determination of prognosis for severe liver disease
-determination of severity and prognosis of Reye's syndrome
-Diagnosis of inherited deficiency of urea cycle enzymes
-monitoring of hyperalimentation therapy
Specimen requirement for ammonia
Venous blood should be obtained without trauma and placed on ice
Heparin and EDTA :)
should be centrifuged at 0-4 C within 20 minutes and plasma and serum removed
Reference intervals for ammonia
Adult:
19-60 ug/dl
Child ( 10 days - 2 years) :
68-136 ug/dl
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