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English: Algorithm for the diagnostic approach to the patient with PAI. The most common causes of PAI are autoimmune destruction of the adrenal cortex in adults and CAH in children. These etiologies can be screened for using 21-hydroxylase antibodies and a baseline serum 17-hydroxyprogesterone level. Males with negative 21-hydroxylase antibodies should be tested for adrenoleukodystrophy with plasma VLCFAs. If these diagnoses are excluded, a CT scan of the adrenals may reveal evidence of adrenal infiltrative processes or metastases. The individual's clinical picture and family history may render some steps in the algorithm redundant or suggest specific genetic syndromes. The latter includes subtypes of autoimmune polyglandular syndromes or specific rare genetic disorders where adrenal failure is part of a broader phenotype. A list of differential diagnoses is provided in Table 2. AHC, adrenal hypoplasia congenita; AI, adrenal insufficiency; VLCFA, very long chain fatty acid. a 17-OH-progesterone >1000 ng/dL is diagnostic for 21-OH deficiency (14). b VLCFA should be measured in the initial evaluation of preadolescent boys. [Adapted from E. S. Husebye, et al: Consensus statement on the diagnosis, treatment and follow-up of patients with primary adrenal insufficiency. J Intern Med. 2014;275:104–115 (181), with permission. © John Wiley & Sons, Inc.]