Derivatization of methylamine and ethylamine followed by LC and fluorescence detection for measurement of urinary clearance

Monomethylamine (MMA) and ethylamine (EtA) accumulate in uremia. However, the urinary clearances of these compounds in normal humans and those with chronic kidney disease (CKD) have not been studied. In this work, an LC based fluorescence assay for MMA and EtA was developed. In applying the method, we found that some previous assays of urinary levels of MMA and EtA lead to overestimations. Normal subjects with average creatinine clearance of 82 ± 21 mL min^-1 demonstrate clearances for the two aliphatic amines less than the creatinine clearance, and in the range of urinary urea clearance. CKD subjects with an average creatinine clearance of 37 ± 12 mL min^-1 had modestly but significantly elevated serum levels of MMA and EtA above normals. Their fractional clearances were increased markedly compared to normals, mitigating the rise in their plasma levels. These findings imply enhanced secretion and/or reduced reabsorption of the amines with CKD.