[Elevated serum creatinine without discernible kidney disease]

A 46-year-old previously healthy man was incidentally found to have an elevated serum creatinine concentration of 2,7 mg/dl (250 micromol/l) in a dry chemical enzyme test. He had no symptoms. Physical examination was unremarkable.

12 days after the first laboratory test serum creatinine was to be normal (0,66 g/dl, 58 micromol/l). Urinalysis and ultrasound scan of the kidneys revealed no anomalies. But increased sarcosine levels were found in both urine and plasma.

The creatinine testing assay interfered with an elevated serum sarcosine level, which is found in an inborn error of aminoacid metabolism called sarcosinemia.

In a patient with sarcosinemia a dry chemical enzyme analysis which is often used by general practitioners can produce falsely high creatinine levels. When suspecting sarcosinemia, serum creatinine should be checked against another type of laboratory test.