Effect of melanin, oxyhemoglobin and bilirubin on transcutaneous bilirubinometry

The cephalocaudal progression of jaundice was studied in 136 mature, clinically well newborns. The yellow colour of the skin was measured with the transcutaneous bilirubinometer. Significant positive correlation was found between the yellow colour of the skin in four regions and the plasma bilirubin concentration (forehead: rho = 0.83, abdomen: rho = 0.89, knee: rho = 0.82, and foot: rho = 0.65, all P less than 0.00001). The values obtained from the forehead were significantly higher than the values obtained from the abdomen (P less than 0.0001), the knee (P less than 0.00001), and the foot (P less than 0.00001). The cephalocaudal progression of jaundice correlated positively with the plasma bilirubin concentration (rho = 0.58, P less than 0.00001) and inversely with the gestational age (rho = -0.28, P less than 0.01). The results support a proposed hypothesis explaining the cephalocaudal progression of jaundice in newborns. According to the hypothesis, the cephalocaudal colour difference may be caused by the presence of young bilirubin-albumin complexes in the blood undergoing conformational changes.