Transcutaneous bilirubinometry: a noninvasive tool for studying newborn jaundiced rats before and after exposure to...

The homozygous Gunn rat is the most frequently used animal model for the study of neonatal jaundice. We evaluated the applicability of noninvasive transcutaneous bilirubin (TcB) measurements as an index of serum total bilirubin (STB) levels in neonatal rats by comparison to invasive STB measurements. TcB measurements were made during the first 96 h of life with the Model 101 Minolta/Air-Shields Jaundice Meter (JM) and SpectRx BiliCheck System (BC). Measurements with both devices displayed parallel TcB profiles, rapidly rising within 24 h, increasing during the next 6 h, then leveling off after 30 h. Linear regressions for the JM (n = 60) were as follows: STB (mg/dL) = 0.79 (JM) - 0.01 (units, r = 0.95, head); STB (mg/dL) = 0.82 (JM) + 1.51 (units, r = 0.95, upper back); and STB (mg/dL) = 0.74 (JM) + 1.60 (units, r = 0.91, lower back). Mean bias +/- imprecision were as follows: -0.02 +/- 3.99 mg/dL, -0.01 +/- 3.90, and 0.01 +/- 4.28 at the head, upper back, and lower back, respectively. For the BC, only lower back measurements were taken, and the regression was as follows: STB (mg/dL) = 0.77 (BC) + 1.65 mg/dL, (r = 0.93, n = 29) with a mean bias +/- imprecision of -1.08 +/- 3.08 mg/dL. When pups were exposed to light, correlations remained strong but intercepts increased. These results demonstrate that noninvasive TcB measurements correlate highly with STB in the Gunn rat during the first 96 h of life and after exposure to light. We conclude that JM measurements at the head and BC at the lower back reflect STB most reliably and consistently. Thus, in addition to being a useful tool for evaluating jaundice in human neonates, TcB methodology can be used successfully for the noninvasive monitoring of jaundice in neonatal Gunn rats pre- and postlight exposure.