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Transcutaneous bilirubinometry in jaundiced newborns has been extensively evaluated in the literature.1 Information about the new BiliCheck (TcBC) device has appeared in recent years.2,3 Because of the high correlation coefficient, most studies conclude that transcutaneous bilirubinometry could possibly replace the laboratory measurement of serum bilirubin (TSB). However, the number of infants with serum bilirubin levels > 257 μmol/l (15 mg/dl) is too small to assess the accuracy of TcBC for such infants.4,5
We tested the clinical usefulness of this new device and compared it with the established Jaundice Meter (TcBM) by evaluating the levels of agreement, with TSB as the clinically used standard. Bilirubin levels were measured by TcBC, TcBM, and TSB in 122 healthy newborns (gestational age 34–42 weeks, mean 39 weeks; mean (SD) birth weight 3187 (582) g) during the first days of life. For TSB the Vitros 250 BuBc slide was used. For statistical analysis, the correlation coefficients were calculated and the difference plots determined by the Bland-Altman method.6
TSB levels ranged between 13.7 and 339 μmol/l (0.8 and 19.8 mg/dl) (mean 186.6 μmol/l (10.89 mg/dl), median 193.6 μmol/l (11.3 mg/dl)). The correlation coefficient, r, was 0.92 between TcBC and TSB, and 0.85 between TcBM and TSB. The plot of differences of TcBC against TSB yielded a maximum range of −109.9 to +56.5 μmol/l (−6.3 to +3.3 mg/dl), and TcBM against TSB −123.9 to +107.9 μmol/l (−7.23 to +6.3 mg/dl). The 95% limits of agreement were between −61.5 and +55.3 μmol/l (−3.59 and +3.23 mg/dl) for TcBC, and −93.4 and +80.2 μmol/l (−5.45 and +4.68 mg/dl) for TcBM.
Although the correlation coefficients give the impression that TcBC and TcBM provide an accurate estimate of TSB, the differences between transcutaneous measurements with either device and TSB values were often quite large. In particular, if TSB levels were higher than 188 μmol/l (11 mg/dl), the measurements of both instruments progressively deviated to lower bilirubin levels than TSB. This leads to a dangerous underestimation of TSB, especially if a decision on treatment has to be made.
We conclude that transcutaneous bilirubinometry with the BiliCheck can be used as a screening tool in the evaluation of hyperbilirubinaemia, but it cannot replace laboratory measurements of serum bilirubin. Given the wide limits of agreement, we recommend that a venous blood sample is taken, if the difference between a potential phototherapy limit and the TcBC level falls below 60 μmol/l (3.5 mg/dl).