Nonprotein Nitrogen Compounds

. Which one of the following is not an NPN substance? a. Allantoin b. Ammonia c. Creatinine d. Urea

Which compound constitutes nearly half of the NPN substances in the blood? a. Ammonia b. Creatine c. Urea d. Uric acid

A technologist reports urea N of 9 mg/dL. What is the urea concentration for this sample? a. 3.2 mg/dL b. 4.2 mg/dL c. 18.0 mg/dL d. 19.3 mg/dL

Which blood collection tube additive can be used to collect a specimen for measurement of urea? a. Ammonium b. Lithium heparin c. Sodium citrate d. Sodium fluoride

In the clinical laboratory, urea N is measured most often using a. Conductivity b. Enzymatic reactions c. Isotope dilution mass spectrometry d. Multilayer film formats

Elevated blood urea concentration is termed a. Azotemia b. BUN c. Uremia d. Uremic syndrome

Prerenal azotemia is caused by a. Acute renal failure b. Chronic renal failure c. Congestive heart failure d. Urinary tract obstruction

A technologist obtains a urea N value of 61 mg/dL ( 3.3 mmol/L) and a serum creatinine value of 2.5 mg/dL (0.139 mmol/L) on a patient. These results indicate a. Congestive heart failure b. Dehydration c. Glomerular nephritis d. Urinary tract obstruction

Uric acid is the final product of a. Allantoin metabolism b. Amino acid metabolism c. Purine metabolism d. The urea cycle

Sources of error in measurement of uric acid include a. Assay interference b. Competition from alternate purine substrates c. Narrow spectrophotometer bandwidth d. Nonspecific enzyme activity

Which condition is not associated with elevated plasma uric acid concentration? a. Allopurinol overtreatment b. Gout c. Lesch-Nyhan syndrome d. Renal disease

Complete deficiency of hypoxanthine–guanine phosphoribosyltransferase results in which disease? a. Allantoinism b. Glycogen storage disease c. Lesch-Nyhan syndrome d. Megaloblastic anemia

Uric acid nephrolithiasis refers to a. Acidification of the urine to dissolve renal calculi b. Formation of renal calculi composed of uric acid c. Precipitation of urates in the urinary tract d. Saturation of the kidney with uric acid

A 45-year-old male presents to the emergency department complaining of intense joint pain. The previous night the patient experienced similar pain accompanied by inflammation and redness of his wrists and large toe. The physician on-call orders testing for serum uric acid concentration. Which laboratory results and diagnosis are consistent with the physician’s assessment? The reference interval for uric acid is 3.5 to 7.2 mg/dL. a. Uric acid 1.9 mg/dL; Fanconi syndrome b. Uric acid 1.0 mg/dL; hereditary xanthinuria c. Uric acid 9.1 mg/dL; alcoholism d. Uric acid 9.1 mg/dL; gout

Which statement describes creatinine biosynthesis accurately? a. Creatine is phosphorylated in the liver to form phosphocreatinine. b. Creatine phosphate undergoes spontaneous cyclization to form creatinine. c. Creatinine is formed from creatine and creatine phosphate in the liver. d. Creatinine is synthesized from arginine, glycine, and methionine in the liver.

Substances known to increase results when measuring creatinine by the Jaffe reaction include all of the following EXCEPT a. Ascorbic acid b. Bilirubin c. Glucose d. α-Keto acids

. In the Jaffe reaction, a red-orange chromogen is formed when creatinine reacts with a. Aluminum magnesium silicate b. Creatininase c. Phosphocreatine d. Picric acid

Creatinine excretion typically a. Decreases from childhood to middle age b. Does not vary with age and sex c. Is higher for females than for males d. Is highest for adult men aged 18 to 50 years

Use of serum creatinine to calculate GFR a. Is discouraged because the calculations are complex b. Is encouraged as a means to identify kidney disease and improve patient care c. Requires hospitalization of the patient for specimen collection d. Requires simultaneous measurement of creatinine in a 24-hour urine collection

Which factor must be considered for calculation of creatinine clearance using the MDRD equation? a. Certification of body mass index b. Documentation of specimen collection time c. Identification of ethnicity d. Verification that the patient was fasting

Which situation would be expected to falsely increase measured blood ammonia concentration? a. The patient smoked two cigarettes 15 minutes prior to phlebotomy. b. The patient was fasting for 8 hours before blood collection. c. The patient ate a steak dinner the night before the specimen was collected. d. The specimen was placed on ice immediately after collection

Although arterial blood is the recommended specimen for determination of this analyte, it is seldom used. a. Ammonia b. Creatine c. Urea d. Uric acid

Toxic effects of elevated blood ammonia concentration include a. Decreased renal function b. Hemorrhage and dehydration c. Mental status changes and coma d. Pain and inflammation of peripheral joints

Ammonia concentrations are measured to evaluate a. Acid–base status b. Glomerular filtration c. Hepatic encephalopathy d. Renal failure