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P554. Conventional electrochemiluminescence immunoassay method underestimates cortisol suppression in patients with ulcerative colitis treated with oral prednisone

F. Manguso1, R. Bennato1, G. Lombardi1, A. Viola2, E. Riccio1, 1AORN A. Cardarelli, UOC Gastroenterology, Napoli, Italy, 2AORN A. Cardarelli, Hematology and Stem Cell Transplantation, Napoli, Italy

Background

In samples from patients who have been treated with prednisone (PD) concentrations of cortisol may be overestimated by using conventional electrochemiluminescence immunoassay (ECLIA) method. The aim of the study was the quantification of blood cortisol levels by using ECLIA compared to a selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in samples collected from patients with ulcerative colitis (UC) treated with oral PD.

Methods

In a single-center, observational, prospective, registered study, 20 patients both sexes, aged between 18 and 70 years, with acute relapse of UC were treated with a standard scheme of oral PD. All patients had extension of the disease above the rectum and indication for systemic corticosteroid treatment. PD was administered starting at a dose of 40 mg once a day for 2 weeks. At a stable daily dose of 30 mg in the last two weeks, venous blood samples for cortisol levels measurement were drawn in the morning in fasting conditions, at a 24 hour distance from last PD dose. From each sample one aliquot (200 uL of plasma from EDTA-treated blood) was used to determine circulating cortisol by LC-MS/MS assay, and one aliquot (about 1.5 mL of serum from untreated blood) was used to determine circulating cortisol by ECLIA assay.

Results

Median (min–max) blood cortisol levels with ECLIA method were 54.1 (17.7–739.7) nmol/L, while with LC-MS/MS assay were 32.1 (14.0–439.5) nmol/L. The median (min–max) of the within-patient differences between the two methods, was 23.2 (−0.9–363.5) nmol/L reflecting higher cortisol levels measured with the ECLIA method. The estimated geometric mean ratio between methods, based on differences of log transformed data, 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% confidence intervals of the geometric mean ratio between methods confirm a statistically significant difference.

Conclusion

Data obtained with the ECLIA method are higher than the ones measured by LC-MS/MS, indicating overestimation of cortisol levels in patients treated with PD. We conclude that the cortisol suppression in the presence of PD should not be assessed by ECLIA method.