The Renal Threshold of Bilirubin by I. M. Rabinowitch with the Technical Assistance of Eleanor

Determination of t’he renal thresholds of the different blood constituents in man-the concentrations of these substances in the blood at which they appear in the urine-is difficult for a number of reasons. Experiences with glucose may be cited as an example of the many possible physiological and technical variables. It is, perhaps, the difficulty of controlling these variables which has made it doubtful whether the renal threshold concept is applicable to any blood constituent; and bilirubin affords no exception. This blood pigment presents additional difficulties in that it does not lend itself very well to ingestion, because of the destructive action of the secretions and bacteria of the gastrointestinal tract. Nor does bilirubin readily lend it,self to intravenous injection, because of its solubility properties and the difficulty of simulating in the injected fluid the physical state in which bilirubin normally circulates in the blood stream. The problem is further complicated by the present status of our knowledge of the van den Bergh reaction-the only practical method at present available for the detection of bilirubin when present in very small quantities. Van den Bergh did not regard the method as strictly quantitative, but considered it sufficiently so to afford a fairly accurate index of progress of individuals suffering from jaundice, Fischer and Barrenscheen (l), unable to obtain complete coupling of the diazo reagent with simple solutions of bilirubin, concluded that the procedure is unreliable for quantitative work. More recently, however, Hunter (2) has shown that, under suit’able conditions, coupling of diazobenzene-p-sulfonic acid with bilirubin is complete; that with simple solutions there is