The 1 μg cosyntropin test in normal individuals: A reappraisal

The 1μg cosyntropin test has some advantages over the 250μg test as a test of adrenal function. One of the concerns regarding the 1 μg test includes stability of the cosyntropin when reconstituted and stored. Classically the 5(th) percentile responses to cosyntropin in normal individuals have been used to define a normal response. Recent studies have shown that these normative values should be determined for individual assays.

We performed a 1μg cosyntropin test using reconstituted and refrigerated (4-8(°) C) cosyntropin in saline solution in 49 non pregnant adults who were apparently healthy and had no exposure to exogenous glucocorticoids. The cosyntropin solution was stored for up to 60 days following reconstitution. We analysed the data for any association between duration of cosyntropin solution storage and the cortisol responses to cosyntropin administration.

The mean ± SD cortisol level at baseline, 30 and 60 min were-12.19 ± 3 μg/dl, 20.72 ± 2.63 μg/dl, 16.86 ± 3.33 μg/dl. The 5(th) percentile cortisol response at 30 min was 16.5 μg/dl (16.33 μg/dl rounded off). The correlation coefficients between number of days of cosyntropin solution storage and the cortisol responses at 30 and 60 min were (Spear mans rho = 0.06,-0.24 respectively) (P = 0.69 and 0.41). There were no differences in cortisol values whether the storage was for less than 30 days or more than 30 days (mean difference 0.25 μg/dl P = 0.44).

The 5(th) percentile normative values determined for our assay is lower than what is currently being used clinically and in research publications. Prolonged refrigerated storage of cosyntropin solution does not affect the validity of the 1 μg cosyntropin test.