The Metabolism of Bile Pigments in Infants, with Special Regard to Icterus Neonatorum

Summary. Previous investigations into the metabolism of bile pigments in infants, especially with regard to icterus neonatorum are discussed as well as the theories advanced to interpret the origin of icterus neonatorum. After briefly describing the analytical methods used—which presumably are both specific and quantitative—the material of the authors is presented. It comprises determinations of the serum bilirubin in 90 new‐borns, 35 of whom were subjected to serial determinations during the first 10 days of life. In 25 of the cases also the fecal output of bilirubin was determined and in 20 cases the urinary bilirubin. Finally, the fecal urobilin was determined in 28 infants. The variation of the serum bilirubin is illustrated (Diagram 1, 4 and 2). The direct diazo reaction of the serum was measured and corresponded to 50–80% of the total serum bilirubin. The serum bilirubin threshold for clinical jaundice was found to be ca. 9 mg. per 100 ml. in newborns against ca. 2.5 in adults; the cause of this striking difference is discussed. The threshold for the excretion of bilirubin in the urine was found to be ca. 18 mg. per 100 ml. in newborns against 3–9 (most often 3–6) in adults. Moreover, the bilirubin concentration in the urine, expressed in per cent of that of the serum, was found to be considerably lower in newborns than in adults. This striking difference is attributed to physiologically defective kidney function in the newborn. The fecal excretion of bilirubin in newborns is illustrated (Diagram 4). No significant correlation between the degree of jaundice and the fecal excretion is seen (Diagram 5). The fecal excretion shows considerable variation. The amounts present in mecomum are small (often 0). Urobilin is only exceptionally found in the feces during the 1′ and 2′ weeks of life; in bottle‐fed infants it may be found from the third week, and as the diet becomes varied, its occurrence in the feces becomes more regular while bilirubin disappears from the feces (Table 4). The total amount of urobilin (+ urobilinogen) excreted with the feces in infants is relatively small compared with the findings in adults. The substances found in feces and urine from newborns by means of reactions based on fluorescence are not urobilin; the results of analyses of this kind are misleading. A considerable part of the bile pigments coming into the intestine is destroyed during the process of digestion; one cannot conclude from the amount of bilirubin + urobilin in the feces to the amount of bile pigment which has passed through the common bile duct into the intestine. The most probable theory of the origin of icterus neonatorum seems to be the hepatic. It lacks, however, positive support from analyses of the bile pigment metabolism. Some other evidence pointing to hepatic dysfunction in the newborn is cited.