D. Doskiy 1, J.A.P. Bons2, J.J.G. Hillebrand3, S.A.A. van den Berg1
1 Department of Internal Medicine, Erasmus MC, Rotterdam, The Netherlands
2 Central Diagnostic Laboratory, Maastricht UMC+, Maastricht, The Netherlands
3 Department of Laboratory Medicine, Amsterdam UMC, Amsterdam, The Netherlands
Introduction
Adrenal insufficiency is a life-threatening condition. Cortisol measurements, 30 minutes after ACTH stimulation, form the diagnostic basis. Platform-dependent cutoff values are necessary, which led to a national harmonisation study. From this, we found that the Roche Cobas platform, on average, performs comparably to a JCTLM-calibrated LC-MS/MS method. However, it is known from EQA proficiency testing that within this group between-laboratory differences may be clinically relevant. We investigated this using a method comparison of ACTH stimulation tests.
Methods
Based on SKML results (series 2024), six Roche users were selected. Laboratories received 21 samples originating from 7 ACTH stimulation tests (3 abnormal, 4 normal). Concentration assignment was performed using a JCTLM-calibrated LC-MS/MS method (ERM-DA451/IFCC). Method differences were interpreted in clinical context by allowing a maximum bias of 25 nM at 30 minutes post ACTH stimulation.
Results
Across the measurement range, Passing-Bablok and Bland-Altman analysis showed a significant relative and absolute method difference of 6% (range 1-11%) and 18 nM (range -1 – 38 nM). At the diagnostic 30-minute time point, mean bias was 19 nM (range –15 to 69 nM). In 15 of 42 results (from five different laboratories) a method difference >25 nM was found, and in 8 of 42 results >35 nM.
Conclusion
In line with previous findings, the Roche cortisol user group performs with only a small mean deviation of 6% (14.5 nM) compared with a JCTLM-calibrated LC-MS/MS method. However, in a substantial number of individual measurements a difference >25 nM during ACTH stimulation testing was observed, which may lead to incorrect diagnosis of adrenal insufficiency.