Microchemical examinations of the blood are being more and more utilized as aids in the rational diagnosis, prognosis and treatment of disease. Probably no other disease offers as great a variety of chemical changes as that involving cases of renal insufficiency with concomitant retention of many of the urinary constituents. Among these compounds are such familiar chemical entities as urea, creatinine, uric acid, phosphorus and other substances, the variations and clinical significances of which are well known. Circulating in the blood stream, however, are a considerable number of unexamined or ill defined substances awaiting identification and clinical evaluation.
In 1924, while working on the van den Bergh reaction, C. H. Andrewes discovered a new diazo color reaction which seemed to be given only by uremic serums.1 The diazo reagent, diazobenzene sulphonic acid, is a familiar laboratory reagent which has been found to couple with a variety of substances yielding variously