Multicenter comparison of three automated procalcitonin (PCT) assays and commutability evaluation of EQA/PT materials

The aim of this study is to assess the comparability of three commercial procalcitonin (PCT) immunoassays, including Kryptor BRAHMS PCT sensitive, Beckman Coulter DXI 800 Access PCT and Roche BRAHMS PCT, and to evaluate the commutability of four types of External Quality Assessment/Proficiency Tests (EQA/PT) materials among the three assays.

The limits of quantitation or functional sensitivity (LoQ/FS) for the three PCT assays were validated according to the CLSI EP17 guidelines. Precision was verified at 0.5 μg/L and 2 μg/L according to CLSI EP15 document. A method comparison study was conducted using 506 clinical serum samples from individual patients. Seventeen EQA/PT materials, including frozen pooled human serum (FFS), lyophilized materials (Lyo), bovine serum albumin solution (BSA) with recombinant PCT, and human serum (HS) with recombinant PCT, were tested together with 50 clinical individual serum samples. The commutability of EQA/PT materials was evaluated using the difference in bias approach.

The LoQ/FS and imprecision of all three assays met the claimed standards. Pairwise comparisons demonstrated high correlations ranging from 0.994 to 0.998 (all p < 0.0001), with relative biases between -13.9% and 23.3%. Clinical consistency at thresholds of 0.1 μg/L, 0.25 μg/L, 0.5 μg/L, 2.0 μg/L, and 10 μg/L exceeded 95% across all methods. The commutability of the four EQA/PT material types was generally poor. The proportions of commutable results were 6/18 for Lyo, 1/15 for BSA, 5/15 for HS, and 7/12 for FFS, with FFS showing the highest commutability among the materials tested.

The assays meet clinical requirements for PCT testing. Among the four EQA/PT materials evaluated, the HS, Lyo, and BSA materials demonstrated limited commutability. Although FFS does not exhibit full commutability, it is considered the most suitable EQA/PT material among those tested. Some residual non-commutability still exists and warrants further investigation.