The marker of cobalamin deficiency, plasma methylmalonic acid, correlates to plasma creatinine

Objective. To examine the relationship between the two diagnostic tests, pl asma methylmalonic acid and plasma cobalamins, and their association with p lasma creatinine, age and sex. Design. Cross-sectional study of simultaneous laboratory measurements. Setting. County of Aarhus, Denmark. Subjects. Records on 1689 patients who had their first plasma methylmalonic acid measurement during 1995 and 1996, and who had a simultaneous measurem ent of plasma cobalamins. Plasma creatinine values measured within a week o f measurements of plasma methylmalonic acid and plasma cobalamins were avai lable for 1255 of the patients. Main outcome measures. Predictors of variation in plasma methylmalonic acid ; plasma cobalamins, plasma creatinine, age and sex. Results. Plasma methylmalonic acid was positively correlated with plasma cr eatinine, even for plasma creatinine within the normal range. These associa tions remained in a multiple regression analysis. For plasma cobalamins bel ow 200 pmol L-1, there was a strong negative correlation between plasma met hylmalonic acid and plasma cobalamins, whilst the association was weak for higher plasma cobalamin levels. Plasma methylmalonic acid increased and pla sma cobalamins decreased with age. Conclusions. The strong correlation between plasma methylmalonic acid and p lasma creatinine suggests that plasma creatinine - also within the normal r ange - must be taken into consideration when interpreting plasma methylmalo nic acid.