Delay in separating blood samples affects creatinine measurement using the Roche kinetic Jaffe method

Abstract

Background We have examined the effect of delayed sample separation on serum creatinine measurement using the kinetic Jaffe method and estimated glomerular filtration rate (eGFR), and the impact this can have on chronic kidney disease (CKD) staging. Methods In a preliminary study clotted samples were left at room temperature for up to 48 h prior to centrifugation and serum creatinine measurement on a Roche modular analyser. A larger study then used paired clotted samples separated at baseline (30 min) and after 24 h at room temperature. To determine the effect on CKD staging, eGFR was calculated using the simplified [4-v] Modification of Diet in Renal Disease formula. Results Preliminary study. A significant increase in creatinine concentration ( P < 0.001) occurred after a 16 h delay in sample separation. By 48 h the mean increase in creatinine was 29% (range 21–63%). Twenty-four hour delay study. The mean increase in creatinine for 113 outpatient samples after delaying sample separation by 24 h was 11%, and exhibited considerable individual variation (range 2–87%). CKD staging for 32% of the group changed, 26% from stage 1 to 2 and 6% from stage 2 to 3. Conclusions Delay in sample separation affects the creatinine measurement using the Roche kinetic Jaffe reaction, and can result in the misclassification of CKD staging. Laboratories using the kinetic Jaffe method should not report creatinine results where there has been a delay in separation. This advice should also be reflected in practice guidelines.