The influence of ketoacids on plasma creatinine assays in diabetic ketoacidosis.
OBJECTIVE
Analysis of the interference of ketoacids on various routine plasma creatinine assays during a clinical episode of diabetic ketoacidosis (DKA).


METHODS
Observational study. Blood samples were drawn before, during and after standard in-hospital treatment. Plasma creatinine was measured with two dissimilar enzymatic assays (creatininase PAP + and creatinine iminohydrolase Serapak), a kinetic alkaline picrate method (Jaffé) and a high-performance liquid chromatography (HPLC) procedure. Acetoacetate and beta-hydroxybutyrate were analysed by enzymatic methods.


METHODS
Department of Medicine, University Hospital.


METHODS
Nine patients who experienced 10 episodes of DKA.


METHODS
Agreement of the routine plasma creatinine assays with HPLC and analysis of possible interferents.


RESULTS
At presentation, the Jaffé assay gave falsely high values of plasma creatinine (median 99 micromol L(-1)), in contrast to the PAP+ (median 60.5 micromol L(-1)) and HPLC assays (median 67.5 micromol L(-1)). This positive error decreased during treatment. This was due to a decrease in acetoacetate, as the positive error by the Jaffé method correlated with the acetoacetate concentration (r = 0.79, P < 0.0001). In the multiple regression analysis, beta-hydroxybutyrate caused no additional interference by the Jaffé assay, confirmed by in vitro experiments. Analysis of agreement showed that the difference between PAP+ and HPLC creatinine was -4.6 +/- 3.0 micromol L(-1) (mean +/- SD), and 2.0 +/- 5.3 micromol L(-1) between Serapak and HPLC. This was statistically significant, but clinically negligible.


CONCLUSIONS
Acetoacetate caused severe interference of the alkaline picrate (Jaffé) assay, which might influence therapeutic decisions at the start of diabetic ketoacidosis. Enzymatic assays lack this interference.
Kemperman
F A
FA
Department of Internal Medicine, Academic Medical Centre, University of Amsterdam, The Netherlands. M.A.Zeeman@amc.uva.nl
Weber
J A
JA
Gorgels
J
J
van Zanten
A P
AP
Krediet
R T
RT
Arisz
L
L
D000328:Adult; D002851:Chromatography, High Pressure Liquid / Q000379:methods / Q000706:statistics & numerical data; D004796:Clinical Enzyme Tests / Q000379:methods / Q000706:statistics & numerical data; D003404:Creatinine / Q000097:blood*; D016883:Diabetic Ketoacidosis / Q000097:blood* / Q000175:diagnosis; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007651:Keto Acids / Q000097:blood*; D008297:Male; D012044:Regression Analysis; D013997:Time Factors
D007651:Keto Acids; D003404:Creatinine