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The influence of a cooked-fish meal on estimated glomerular filtration rate

Background Ingestion of cooked meat increases circulating blood creatinine concentration due to conversion of creatine during cooking. This may cause falsely low estimated glomerular filtration rate. National Institute for Health and Care Excellence chronic kidney disease guidelines recommend meat avoidance prior to blood testing for estimated glomerular filtration rate. Fish muscle also contains creatine, but the influence of fish consumption on blood creatinine concentration has not been studied. Method Four blood samples were collected from each of 20 healthy volunteers: one before and three (at 2, 4 and 20 h) after consuming cooked fish (200 g/person cod, approximately 35 g/person protein). Apart from this meal, for the study duration, subjects were asked to avoid eating meat or fish. Creatinine and cystatin C were measured and estimated glomerular filtration rate (CKD-EPI equations) was calculated. Results Serum creatinine concentration (mean) was increased relative to the preprandial concentration (71.8 μmol/L) in all subjects at 2 h (77.3 μmol/L) and in 17/20 subjects at 4 h (75.5 μmol/L) (P < 0.0001) but was not significantly different from baseline after 20 h (73.6 μmol/L P = 0.1170). Mean cystatin C concentration remained unchanged throughout the study (P > 0.05). Estimated glomerular filtration rate calculated using the CKD-EPI (creatinine) and CKD-EPI (creatinine and cystatin C) equations demonstrated significant declines at 2 and 4 h (P < 0.0005), while the CKD-EPI (cystatin C) equation remained unchanged (P > 0.05). Conclusion Cooked fish consumption transiently increases blood creatinine concentration and consequently lowers the estimates of glomerular filtration rate derived from creatinine-based equations. Consideration should be given to avoidance of cooked fish consumption before glomerular filtration rate estimation.