MLT Review-NPN -10Q

A patient with a hematologic malignancy is prescribed rasburicase to prevent unwanted side effects of chemotherapy. In the laboratory, it is an interfering substance in the measurement of what non-protein nitrogen?

• Urea

• Creatinine

• Ammonia

• Uric acid

Which of the following is the best practice for specimen collection and handling of specimen for ammonia measurement?

• Draw specimen in a serum separator tube, preventing the need to separate serum from cells, centrifuge specimen, and test immediately.

• Draw sodium heparin tube, place on ice immediately, centrifuge specimen in refrigerated centrifuge, separate cells from plasma within 20 minutes, and test immediately.

• Draw EDTA specimen, place on ice, centrifuge, separate serum from cells within 1 hour of collection, protect from light, test immediately.

• Draw fasting specimen in a plasma separator tube containing lithium heparin, place on an ice pack, centrifuge at 20° C, test immediately.

Which of the following statements concerning urea is true?

• It is generated in the liver from nucleic acid breakdown.

• It is formed from amino groups (-NH₂) and free ammonia.

• It is increased in inherited deficiencies of urea cycle enzymes

• It is increased in the serum during acute episodes of gout.

Blood ammonia levels are used to evaluate which of the following conditions?

• Hepatic encephalopathy

• Acute renal failure

• Chronic renal failure

• Uremic syndrome

Answer explanation

Hepatic encephalopathy is caused when toxins that are normally cleared from the body by the liver accumulate in the blood, eventually traveling to the brain. Many of the symptoms of hepatic encephalopathy are reversible when promptly detected and treated.

Creatinine is formed from the:

• Oxidation of creatine

• Oxidation of protein

• Deamination of dibasic amino acids

• Metabolism of purines

Creatinine is considered one of the substances of choice to measure endogenous renal clearance because:

• The rate of formation per day is independent of body size.

• It is completely filtered by the glomeruli

• Plasma levels are highly dependent upon diet

• Clearance is the same bo both men and women

Select the primary reagent used in the Jaffe method for creatinine measurements

• Alkaline copper II sulfate

• Saturated picric acid and sodium hydroxide

• Sodium nitroprusside and phenol

• Phosphotungstic acid

A patient's BUN is 60 mg/dL and serum creatinine is 3.0 mg/dL. These results suggest:

• Laboratory error measuring BUN

• Renal failure

• Prerenal failure

• Patient was not fasting

Uric acid is derived from:

• Oxidation of proteins

• Catabolism of purines

• Oxidation of pyrimidines

• Reduction of catecholamines

Which of the following formulas is the correct expression for creatinine clearance?

• U/P x V x 1.73/A

• P/V x U x A/1.73

• P/V x U x 1.73/A

• U/V x P x 1.73/A