Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (870 page)

   Drugs that may decrease the urine CrCl include acetylsalicylic acid, amphotericin B, carbenoxolone, chlorthalidone, cimetidine, cisplatin, cyclosporine, guancydine, ibuprofen, indomethacin, mitomycin, oxyphenbutazone, paromomycin, probenecid (coadministered with digoxin), and thiazides.

   Excessive ketones in urine may cause falsely decreased values.

   Failure to follow proper technique in collecting 24-hour specimen may invalidate test results.

   Failure to refrigerate the specimen throughout the urine collection period allows decomposition of creatinine, causing falsely decreased values.

   Consumption of large amounts of meat, excessive exercise, and stress should be avoided for 24 hours before the test.

Suggested Reading

National Kidney Foundation KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification.
http://www.kidney.org/professionals/kdoqi/guidelines_ckd/p5_lab_g4.htm
. Accessed November 18, 2010.

CREATININE WITH ESTIMATED GLOMERULAR FILTRATION RATE (eGFR)

   Definition

   Creatinine is formed by the hydrolysis of creatine and phosphocreatine in muscle and by ingestion of meat. It is freely filtered at the glomerulus and secreted at the proximal tubule; some is resorbed. GFR is equal to the total of the filtration rates of the functioning nephrons in the kidney.

   
Normal range:

   
Creatinine

   0–1 month: 0.00–1.00 mg/dL

   1 month–1 year: 0.10–0.80 mg/dL

   1–16 years: 0.20–1.00 mg/dL

   >16 years, female: 0.50–1.20 mg/dL