dromlakhani Confirm acromegaly with GH suppression after OGTT
STEP 1 — Gather Information
Obtain serum IGF-1; if elevated or equivocal, proceed to an oral glucose tolerance test (OGTT) with 75 g glucose after an overnight fast, measuring plasma glucose and GH at baseline and intervals (e.g., 0, 30, 60, 90, 120 min) to confirm hyperglycemia and assess GH suppression.
STEP 2 — Rule In / Rule Out
Is the nadir GH concentration after OGTT <1 µg/L? If yes, rule out acromegaly (sufficient suppression); if no (GH ≥1 µg/L), rule in acromegaly (lack of suppression).
STEP 3 — Classify or Stratify
Classify as confirmed acromegaly when GH is not suppressed (GH ≥1 µg/L) and IGF-1 is elevated or equivocal; otherwise consider alternative diagnoses or repeat testing.
STEP 4 — Decide
If acromegaly is confirmed, refer for pituitary MRI to evaluate tumor size and extent; if not confirmed, repeat IGF-1 evaluation and consider other causes of IGF-1 alteration.
Clinical Guardrails / Mimics / Pitfalls
Ensure documented hyperglycemia during OGTT to validate the test; avoid relying on random GH measurements; be aware of assay limitations at low GH levels and conditions that may cause false‑positive GH nonsuppression (e.g., malnutrition, renal failure, hypothyroidism).
Concrete Clinical Example
A 48‑year‑old patient with progressive shoe‑size enlargement and borderline elevated IGF‑1 undergoes a 75‑g OGTT; glucose peaks at 210 mg/dL and nadir GH is 1.4 µg/L. Lack of suppression confirms acromegaly, prompting pituitary MRI which reveals a 12‑mm macroadenoma.
Source: Acromegaly: An Endocrine Society Clinical Practice Guideline, Endocrine Society, 2014, DOI:10.1210/jc.2014-2700
TODO: consider adding scripts/calc.py for the endo-confirm-gh-suppression-ogtt calculator