Salivary Creatinine Assays as a Potential Screen for Renal Disease

Salivary creatinine concentrations are 10–15% of serum creatinine concentrations in healthy populations but have not previously been measured in patients with renal disease. The Cobas Mira automated Jaffe method was adapted to measure salivary creatinine concentration. The method was linear to 1200 μmol/L, had a mean recovery of 78% and a detection limit of 6 μmol/L. Intra-assay variability was 13·5, 5·5 and 1·4% at 10·6, 17·8 and 128·4 μmol/L, respectively. Inter-assay variability was 35·0 and 4·8% at 6·2 and 130·4 μmol/L, respectively. The median salivary creatinine concentrations was 8·5 μmol/L (range 6–18 μmol/L) in healthy subjects (n = 23), and 84 μmol/L (range 18–591 μmol/L) in patients with renal disease (n = 25). Salivary and serum creatinine concentrations were not related in healthy subjects, however, a significant relationship was found in the patients (r = 0·784, P < 0·001). Using salivary creatinine concentration of 16·8 μmol/L as a cut off value, all patients would have been detected with one false positive result (sensitivity 100%, specificity 95·7%, efficiency 97·7%). Thus, salivary creatinine estimations may be used to identify subjects with serum creatinine concentrations above 120 μmol/L.