Evaluation of the Accuracy of Cr and BUN Using the ABL90 FLEX PLUS Blood Gas Analyzer and the Equivalence of Candidate Specimens for Assessment of Renal Function

Background: The ABL90 FLEX PLUS (Radiometer) is a blood gas analyzer that also provides creatinine (Cr) and blood urea nitrogen (BUN) results. We assessed the accuracy of the ABL90 FLEX PLUS to measure Cr and BUN and find suitable candidate specimens against primary specimens (heparinized whole-blood (H-WB)). Methods: Paired H-WB, serum, and sodium-citrated whole-blood (C-WB) samples (105) were collected. The Cr and BUN levels in the H-WB using the ABL90 FLEX PLUS were compared with those of the serum using four automated chemistry analyzers. The suitability of the candidate specimens was assessed at each medical decision level according to the CLSI guideline EP35-ED1. Results: The respective mean differences of the ABL90 FLEX PLUS for the Cr and BUN were below −0.10 and −3.51 mg/dL compared to the other analyzers. The systematic differences between the serum and the H-WB at the low, medium, and high medical decision levels were all 0% for Cr, but those of the C-WB were −12.96%, −11.81%, and −11.30%, respectively. Regarding imprecision, the SD(serum)/SD(H-WB) ratios at each level were 0.14, 1.41, and 0.68, whereas the SD(C-WB)/SD(H-WB) ratios were 0.35, 2.00, and 0.73, respectively. Conclusions: The ABL90 FLEX PLUS provided Cr and BUN results comparable with the four widely used analyzers. Among the candidates, the serum was suitable for Cr testing using the ABL90 FLEX PLUS, while the C-WB did not satisfy the acceptance criteria.