Sensitivity and specificity of the macimorelin test for diagnosis of AGHD

OBJECTIVE: The macimorelin test is approved for the diagnosis of adult growth hormone deficiency (AGHD) based on its efficacy vs the insulin tolerance test (ITT). Macimorelin has a significant advantage over ITT in avoiding hypoglycemia. Analyses were conducted to determine whether macimorelin performance is affected by age, body mass index (BMI), or sex, and evaluate its performance vs ITT over a range of GH cutpoints.

DESIGN: Post hoc analyses of data from a previous randomized phase 3 study included participants aged 18-66 years with BMI <37 kg/m2 and high (Group A), intermediate (Group B), or low (Group C) likelihood for AGHD based on pituitary history, and matched controls (Group D).

METHODS: Probability of AGHD was estimated using unadjusted, age-adjusted, BMI-adjusted, and sex-adjusted logistic models. Area under the curve (AUC) of the estimated receiver operating characteristic (ROC) curve (range, 0-1; 1=perfect) was compared for adjusted vs unadjusted models. Separate analyses evaluated agreement, sensitivity, and specificity for macimorelin and ITT using cutpoints of 2.8, 4.0, 5.1, and 6.5 ng/mL.

RESULTS: For participants in Group A (n=41) and Group D (n=29), unadjusted, age-adjusted, BMI-adjusted, and sex-adjusted models had ROC AUCs (95% CIs) of 0.9924 (0.9807-1), 0.9924 (0.9807-1), 0.9916 (0.9786-1), and 0.9950 (0.9861-1), respectively.

CONCLUSIONS: Macimorelin performance was not meaningfully affected by age, BMI, or sex, indicating robustness for AGHD diagnosis. Of the 4 GH cutpoints evaluated, the cutpoint of 5.1 ng/mL provided maximal specificity (96%) and high sensitivity (92%) and was in good overall agreement with the ITT at the same cutpoint (87%).