Endocrine Abstracts

Introduction: Pharmacologically induced false positive results in urinary free cortisol levels (UFCL) have been ascribed to 11βHSD-2 inhibition or direct interference on HPLC. Few drugs have been implicated by mechanisms not yet confirmed.

Case Reports: We report 3 patients with active pulmonary tuberculosis (TB) and very high UFCL, 2-6× above the upper limit of reference [mean levels 3411 μg/24 h (RR 167-827)]. The 2 males and the woman aged 31 to 60 y.o. had hypertension, one had diabetes mellitus and the other HIV. None had stigmata of Cushing syndrome. Known causes of falsely elevated UFCL were not found (eg. polyuria, synthetic steroid use). Acute disease could justify hypercortisolism but we kept the patients under observation to confirm UFCL normalization. On the first out-patient appointment the UFCL remained very high (mean 2431 μg/24 h) 1, 5 and 6 months after hospital discharge. On the second out-patient appointment, after completion of the anti-TB (HRZE) treatment, all patients had normal UFCL (mean 477 μg/24 h). We reviewed the files for active diseases, comorbidities and treatments: the one common situation was active TB and though acute disease could justify hypercortisolism initially, we considered it less likely to justify the more than 2 fold UFCL elevation in the clinically stable patient after hospital discharge. The drugs used by the 3 patients during hospitalization, continued after the first and discontinued before the second out-patient appointments were Isoniazid and Rifampicin, which we suspect to cause this previously undescribed pharmacological interference. Rifampicin has been implicated in false positive dexamethasone suppression tests.

Conclusions: We report the association of very high UFCL in patients without stigmata of Cushing syndrome treated with anti-TB regimens containing Isoniazid and Rifampicin. Hopefully in the future we will confirm the underlying mechanism and appraise the impact of this finding on the exclusion criteria for adrenal insufficiency in these specific group of patients.