Sacramento, California

Correspondence: Lavjay Butani, M.D., Section of Pediatric Nephrology, Department of Pediatrics, University of California Davis Medical Center, 2516 Stockton Boulevard, Ticon II, 3rd Floor, Sacramento, CA 95817, USA E-mail: Lavjay.butani@ucdmc.ucdavis.edu

To the Editor: Because of the ease in its determination, the serum creatinine concentration (S_cr) has been used as a quantitative marker of renal function in place of the more time-consuming, but also more accurate, methods such as the inulin clearance. However, the impact of dietary protein intake on the determination of S_cr, even by newer enzymatic techniques, remains unappreciated. A previous report described elevations in the S_cr in healthy volunteers after ingestion of beef¹. However, the technique used for S_cr determination, the Jaffe method, is affected by noncreatinine chromogens, and may give falsely elevated values compared to the more sensitive enzymatic assays. We studied the effect of animal protein intake on S_cr, as determined by the Ektachem 700XRC analyzer using a 2-point rate creatinine assay performed at 37° (Johnson and Johnson Clinical Diagnostics, Rochester, NY, USA) in five healthy adult volunteers (mean age, 43 years).

A baseline S_cr was obtained followed by the intake of 300 g of animal protein of different sources at 1-week intervals (cooked beef stew, turkey breast and ham). Three hours after the protein intake, a repeat S_cr was obtained. We found that the mean S_cr rose by 98.5% (range, 69.2% to 128.6%, P < 0.0001, two-tailed paired Student t test) compared to the baseline S_cr after eating beef. The rise was lower with turkey, although still significant (16.2%, P < 0.0001), and insignificant with ham (10.9%, P = 0.13).

We concluded that the S_cr, even as determined by the newer enzymatic methods, is influenced by dietary protein intake to variable degrees; this rise may be even more exaggerated in patients with renal disease. We, therefore, suggest that in the absence of more data, the S_cr, especially in a research study setting, should be measured in the fasting state in all patients.