Accurate direct spectrophotometric bilirubin measurement combined with blood gas analysis

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)).

Quantitation of B(U), B(C), and B(T) (with calculation of B(D)) using a Vitros 250 analyzer served as the comparison method.

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.

This new method overcomes the limitations observed in earlier spectrophotometric methods, and provides accurate results in specimens containing a range of bilirubin forms.