Chromatography and electrophoresis of creatinine and other guanidino compounds

Chromatographic methods, in general, are considered as the definitive and reference procedure. The HPLC procedures reviewed all seem to provide improved and adequate specificity and sensitivity for CRN assay. The HPLC methods are relatively easy to use, have nearly complete recoveries (greater than or equal to 95%) and have good precision. The within- and between-day variations are often less than 4% [85,87,90,94-97,99]. Most of the methods developed [84,85,90,91,94,97,99] were tested for potential interference and the specificity for CRN was demonstrated. One important advantage of the HPLC method [85] is that the presence of an interfering substance in the biological sample can most likely be detected by its influence on the sharpness and resolution of the CRN peak. It is understandable that there are possibilities that other constituents in the biological sample may also be co-eluting with CRN and the investigator should carefully examine the chromatogram obtained for any sign of interference. Ginman and Colliss [107] reported that azathioprine, cyclosporin A, cefotaxime and prednisolone used in patients after renal transplant interfered with the HPLC assay: the results are 40% higher than those by Jaffe method. These interferences, however, were corrected with a slight modification of the HPLC conditions [107]. Because of the non-specificity associated with the Jaffe reaction, the results obtained from Jaffe-based assays often exceed those from HPLC methods [95,108,109]. Such overestimation would be especially significant when the serum CRN is in the normal range where small changes may be indicative of a significant change in a patient's renal function [95,111]. It appears that HPLC methods are the methods of choice for simultaneous analysis of endogenous guanidino compounds. Depending on the purpose of analysis, one would choose a particular type of method, e.g., one among those representative methods listed in Table 1. If one is interested in measuring MG and GSA levels in serum or plasma, then depending on the sensitivity requirement and available instrumentations, one could choose many method listed in Table 1. However, if one needs to measure AARG, ARG and ARA, in addition to MG and GSA, then method 4 in Table 1 would be more appropriate. If TAU is the compound of interest, then one of the methods 2,3,4,5, and 7 with an appropriate deproteinization procedure would be desirable.