Creatinine

A renal function test used in eGFR calculation.²

High creatinine: Renal diseases and insufficiency with decreased glomerular filtration, urinary tract obstruction, reduced renal blood flow including congestive heart failure, shock, and dehydration; rhabdomyolysis can cause elevated serum creatinine. Low creatinine: Small stature, debilitation, decreased muscle mass; some complex cases of severe hepatic disease can cause low serum creatinine levels. In advanced liver disease, low creatinine may result from decreased hepatic production of creatinine and inadequate dietary protein as well as reduced muscle mass.³

With reduced renal blood flow, creatinine rises less quickly than urea nitrogen. Concentration of creatinine only becomes abnormal when about half or more of the nephrons have stopped functioning in chronic progressive renal disease. Antibiotics containing cephalosporin lead to significant false-positive values if samples are drawn within four hours of a dose.⁴ With severe renal disease, creatinine is not reliable in the presence of cefoxitin therapy. There is less interference reported from the cephalosporins cephalothin, cephaloridine, cephadrine sodium, and cephaloglycin dihydrate. Lipemia, hemolysis, and bilirubin may interfere.^5,6

Kinetic Jaffe