Efficacy of using total bilirubin values as a guide for screening direct bilirubin requests

Two divergent laboratory approaches to the determination of direct bilirubin were assessed. The first approach, assaying direct bilirubin (DB) on all total bilirubin (TB) requests regardless of TB values, resulted in a true negative rate (normal TB level less than 1.0 mg/dL [less than 17 mumol/L], and DB level, less than 0.4 mg/dL [less than 6.8 mumol/L]) of 98.7% (984/997 specimens) and a low false negative (normal TB level, abnormal DB level) rate of 1.3% (13 of 997). The second approach, assaying DB on physician request and only if the TB level was greater than or equal to 1.0 mg/dL (1.7 mumol/L), resulted in a true negative rate (normal TB level, no liver disease) of 87.7% (150%) of 171 patients) and a relatively low false negative rate (normal TB level, liver disease) of 12.3% (21 of 171) patients. Medical chart review revealed that, with either approach, none of the patients with false negative results with hepatobiliary disease would have been missed clinically, even if the DB assay had not been done. It is possible to screen DB requests using a TB of 1.0 mg/dL (17 mumol/L) as a means to determine whether DB should be assayed.