Creatinine assay by the fuller's earth procedure or by enzymatic determination is adequate for urine but not plasma of mice.

1. Mouse plasma creatinine measured by fuller's earth (15.1 +/- 0.5(41) microM, mean +/- SE) exceeded the same pools read by HPLC [7.5 +/- 0.2(41); P < 0.001]. 2. For mouse urine, the fuller's earth method (3.26 +/- 0.21 mM) slightly exceeded the HPLC method (2.65 +/- 0.18; P < 0.001) with good correlation (r = 0.915, P < 0.001). 3. An enzymatic method (creatinine PAP, Boehringer-Mannheim Diagnostics) for plasma creatinine (5.2 +/- 0.3 microM) was equivalent to HPLC (6.1 +/- 0.1, NS) but with poor correlation (r = 0.23, NS). 4. Creatinine in the urine agreed closely between HPLC (2.84 +/- 0.12 mM) and the enzymatic procedure (2.95 +/- 0.17, NS) with good correlation (r = 0.845, P < 0.001).