Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (872 page)

Increased In

   Diet: ingestion of creatinine (roast meat).

   Muscle disease: gigantism, acromegaly.

   Pre- and postrenal azotemia.

   Impaired kidney function; 50% loss of renal function is needed to increase serum creatinine from 1.0 to 2.0 mg/dL. Therefore, the test is not sensitive for mild to moderate renal injury.

   An increase in serum creatinine occurs in 10–20% of patients taking aminoglycosides and ≤20% of patients taking penicillins (especially methicillin).

Decreased In

   Pregnancy: Normal value is 0.4–0.6 mg/dL. A value >0.8 mg/dL is abnormal and should alert the clinician to further diagnostic evaluation.

   Creatinine secretion is inhibited by certain drugs (e.g., cimetidine, trimethoprim).

   Proxy for reduced skeletal muscle mass.

   Limitations

   Artifactual decrease by:

   Marked increase of serum bilirubin

   Enzymatic reaction (glucose >100 mg/dL)

   Artifactual increase due to