From the Guidelines
The initial test for acromegaly should be an elevated serum IGF1 level in relation to the age-adjusted, sex-adjusted, and Tanner stage-matched normal range, as it is a reliable marker for GH excess 1. When suspecting acromegaly based on clinical features, measuring serum IGF1 levels is the most appropriate first diagnostic step.
Key Points to Consider:
- Elevated serum IGF1 concentration is a reliable marker for GH excess, but marginal or mild elevation in adolescence needs cautious interpretation 1.
- IGF1 values might be falsely normal or low in cases of concurrent severe hypothyroidism, malnutrition, or severe infection, or might be falsely elevated in poorly controlled diabetes mellitus, hepatic and/or renal failure 1.
- Oral oestrogens can also confound detection accuracy by reducing IGF1 generation by the liver 1.
- An oral glucose load test can be considered, but complete suppression of GH can be difficult to achieve in normal adolescence, and the cut-off GH nadirs are 1 μg/l or 0.4 μg/l using sensitive GH assays 1.
Diagnostic Approach:
- Measure serum IGF1 levels and interpret results within a clinical assessment of phenotype, including height velocity, pubertal stage, and bone age 1.
- Consider dynamic pituitary assessment of possible hypofunction and hyperfunction of other anterior pituitary hormones in cases of GH excess 1.
- Offer biochemical screening for pituitary hormone excess to all patients with associated syndromic causes of somatotrophinomas, such as Carney complex, McCune–Albright syndrome, and MEN1 or MEN1-like disease 1.
From the Research
Initial Test for Acromegaly
The initial test for acromegaly, a condition characterized by excess Growth Hormone (GH) production, is:
- Serum IGF-1 measurement, which is recommended as the initial screen for patients with suspected acromegaly 2
Rationale
The rationale behind using serum IGF-1 measurement as the initial test is that:
- IGF-1 levels correlate with clinical features of acromegaly and with the 24-hour mean GH levels 3
- A random GH <0.4 microg/l and IGF-1 in the age- and gender-matched normal range exclude the diagnosis of acromegaly 3
Additional Testing
If the initial test is inconclusive, additional testing may be necessary, including:
- Oral glucose tolerance test (OGTT) with concomitant GH measurement, which is considered the gold standard diagnostic test for acromegaly 2, 3, 4, 5, 6
Considerations
When interpreting the results of these tests, it is essential to consider that:
- GHn and IGF-1 levels represent two different aspects of disease activity in acromegaly 3
- Suppressed GH after OGTT cannot exclude acromegaly, and some patients may have only mild or no clinical presentation of acromegaly 5
- The performance of OGTT may be limited in patients with biochemically active acromegaly but only mildly increased GH output 6