Clinical Chemistry Test Bank Chapter 21 (Kidney Function Test-Screatinine, Urea, and Uric Acid)

1- Which one of the following statements regarding creatinine is correct??

A) Most intraindividual variation in serum creatinine is due to muscle mass.

B) Serum creatinine levels are not affected by renal disease.

C) Creatinine production increases when serum creatinine is elevated.

D) Creatinine is completely reabsorbed (not excreted)by the renal tubules.

... Answer is A)

2- Urea:?

A) biosynthesis is carried out exclusively in the renal system.

B) is 100% reabsorbed (thus not excreted)by the kidney.

C) is decreased in plasma by a variety of renal diseases.

D) concentration in plasma is increased by a high-protein diet.

... Answer is D)

3- Creatinine clearance is used to assess the _____ of a patient.?

A) glomerular filtration rate

B) creatine concentration

C) renal threshold

D) renal hormonal function

... Answer is A)

4- Which of the following is the primary reagent used in the Jaffe reaction for creatinine??

A) Alkaline copper sulfate

B) Phosphotungstic acid

C) Alkaline picric acid

D) Diacetyl monoxime

... Answer is C)

5- A practicing physician at a university student healthcare facility often recommends to student patients that they take large doses of vitamin C (ascorbic acid)to fend off colds during the semester.As director of the chemistry laboratory that serves this facility,you notice a trend in that many of this physician's students' serum creatinine levels are unusually high.You are currently using a type of analysis based on the Jaffe reaction.What might be the cause of the elevated values??

A) High doses of ascorbic acid cause increased hepatic synthesis of bilirubin,which interferes with the enzymes used in the assay.

B) Elevated ascorbic acid in serum produces a Jaffe-like chromogen in this analysis that can be interpreted as increased serum creatinine.

C) It may be that this physician's patients all are exhibiting increased muscle breakdown.

D) The ketones and ketoacids produced from the breakdown of creatinine in the students' serum are interfering with the development of the color reaction.

... Answer is B)

6- Plasma urea concentration:?

A) is a more reliable indicator of renal function than creatinine.

B) can increase because of decreased renal perfusion.

C) is decreased in intrinsic renal failure.

D) is not affected by diet.

... Answer is B)

7- In the measurement of urea,urea is initially hydrolyzed by urease to form ammonium ions.This assay combined with the spectrophotometric measurement of the resulting ammonia is referred to as the:?

A) ammonia-selective electrode method.

B) Berthelot reaction.

C) Jaffe reaction.

D) urea method.

... Answer is B)

8- Urea is produced from:?

A) catabolism of purine nucleosides.

B) phosphorylation of creatine in muscle.

C) reduction of bilirubin.

D) catabolism of proteins and amino acids.

... Answer is D)

9- The major nonprotein nitrogen degradation product of endogenous purines is:?

A) urea.

B) creatinine.

C) uric acid.

D) ammonia.

... Answer is C)

10- Why do values obtained with the Jaffe reactions for creatinine measurement overestimate creatinine concentration by ~20%??

A) The components of the reaction mixture often continue to react at endpoint and synthesize excess creatinine.

B) The rate of Jaffe complex formation is temperature dependent,and excess heat formed by the reaction leads to increased absorptivity and falsely increased creatinine value.

C) Noncreatinine chromogens in the reaction that react with the picrate in the end-point Jaffe methods overestimate true plasma creatinine concentration.

D) Hydroxide concentrations above 0.5 mmol/L produce a decreased degradation of the Jaffe complex.

... Answer is C)

11- Why does persistently acidic urine lead to formation of uric acid renal stones??

A) Uric acid has a pKa of 5.57,which makes it insoluble in acidic solutions.

B) At a pH of 10,uric acid is insoluble and aggregates to form stones.

C) Elevated urine purines cause uric acid crystals to aggregate and form stones.

D) Supersaturation of acidic urine causes calcium to form complexes with uric acid,which is the initial step in stone formation.

... Answer is A)

12- All of the following conditions are associated with hyperuricemia except:?

A) excessive cell turnover as in malignancy treated with chemotherapy.

B) deficiency of hypoxanthine-guanine phosphoribosyl transferase.

C) preeclampsia toxemia.

D) severe hepatocellular disease.

... Answer is D)

13- Creatininase reactions for creatinine assessment:?

A) yield sarcosine and urea.

B) require the addition of potassium ferricyanide to reduce interference.

C) catalyze the conversion of creatinine to creatine.

D) catalyze the conversion of creatinine to N-methylhydantoin and ammonia.

... Answer is C)

14- Uricase is used in the assay of uric acid to:?

A) decarboxylate uric acid to form tungsten blue.

B) oxidize uric acid to form allantoin.

C) reduce uric acid to form allantoin.

D) reduce uric acid to form tungsten blue.

... Answer is B)

15- Primary gout is distinguished from secondary gout by:?

A) decreased renal excretion (increased renal retention)of uric acid.

B) its polygenic basis.

C) having increased dietary intake of purines.

D) the increased catabolism of purines due to chemotherapy.

... Answer is B)

16- A hemolyzed serum sample from an individual is assayed for creatinine and a result is obtained that is decreased compared to the normal reference interval.If this individual has a normal glomerular filtration rate,which one of the following statements is true??

A) The individual's diet contains high levels of protein.

B) The individual must be receiving chemotherapy.

C) The assay must be subject to interference from bilirubin.

D) The assay must be subject to interference from ketones.

... Answer is C)

17- An individual's laboratory results indicate increased serum creatinine and urea values,and his physician's diagnosis indicates a postrenal obstruction.What would the glomerular filtration rate in this individual likely be??

A) Decreased

B) Increased

C) No change

... Answer is A)

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