BACKGROUND: Blood gas analyses are usually required more frequently in preterm neonates than in term neonates. If total bilirubin (TB) levels in whole blood measured using a blood gas analyzer are reliable, blood sampling for total serum bilirubin (TSB) levels alone can be reduced in preterm neonates. We investigated the reliability of measuring TB levels in whole blood from preterm neonates using the latest generation blood gas analyzer. METHODS: TB measured on an ABL90 FLEX blood gas analyzer and TSB analyzed in the hospital laboratory were simultaneously analyzed. TB and TSB levels (300 data sets in 85 preterm neonates) were compared using linear regression and Bland-Altman difference plots. RESULTS: Concordance correlation coefficient analysis showed a strong relationship between TB and TSB levels (a CCC value of 0.94) with a Pearson's coefficient of 0.97 and a bias correction of 0.97. Bland-Altman difference p lots demonstrated that, on average, TB tended to underestimate the TSB, with a mean (95% confidence interval) bias of -0.7 (-0.6 to -0.8) mg/dL. CONCLUSIONS: Whole blood TB levels measured using an ABL90 FLEX are reliable and can lead to a reduction in blood sampling for TSB in preterm neonates.