Accurate direct spectrophotometric bilirubin measurement combined with blood gas analysis

Abstract Background : A new total bilirubin (B T ) method, based on multiple wavelength absorbance measurements, and an algorithm to calculate concentration, were evaluated for accuracy in specimens containing variable amounts of unconjugated bilirubin (B U ), conjugated bilirubin (B C ) and delta (protein-bound) bilirubin (B D ). Methods : Quantitation of B U , B C , and B T (with calculation of B D ) using a Vitros 250 analyzer served as the comparison method. Results : Analysis of neonatal specimens using a preliminary algorithm yielded good overall agreement with the Vitros B T method, but there was considerable variation in the agreement for individual specimens. When specimens from adults selected to yield a range of B C and B D levels were analyzed, the preliminary algorithm underestimated B T . Refinement of the method in the form of a finalized algorithm resulted in elimination of the negative bias seen with specimens with high B D and B C levels, and better agreement for individual neonatal specimens. Conclusions : This new method overcomes the limitations observed in earlier spectrophotometric methods, and provides accurate results in specimens containing a range of bilirubin forms.