Electrochemiluminescence immunoassay method underestimates cortisol suppression in ulcerative colitis patients treated with oral prednisone.

AIM: To evaluate cortisolemia by using conventional electrochemiluminescence immunoassay (ECLIA) method compared to liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in active ulcerative colitis (UC) patients treated with oral prednisone (PD). METHODS: Twenty patients (12 males) with acute relapse of UC started oral PD at a dose of 40 mg once a day, tapered of 10 mg every 2 wk. When a stable 2-wk daily dose of 30 mg was reached, blood samples for cortisol levels' measurement were drawn in the morning in fasting conditions to determine circulating cortisol by LC-MS/MS and ECLIA assay. RESULTS: Median interquartile range cortisolemia with ECLIA and LC-MS/MS method was 54.1 (185.8) nmol/L and 32.1 (124.0) nmol/L, respectively (P < 0.001). The within-patient median differences between the two methods was 23.2 (40.6) nmol/L, with higher cortisol levels for the ECLIA method. The estimated geometric mean ratio between methods was 1.85 (95%CI: 2.39-1.43) considering all data or 1.58 (95%CI: 2.30-1.09) considering only data above the limit of quantification (n = 12). The 95%CIs of the geometric mean ratio between methods confirm a statistically significant difference. CONCLUSION: Blood cortisol levels detected with ECLIA method seems to be higher than the ones measured by LC-MS/MS, indicating a possible overestimation of them in patients treated with PD. Therefore, the cortisol suppression in patients under treatment with oral PD should not be measured using ECLIA method.