From the Guidelines
The initial test for acromegaly should be an assessment of growth hormone (GH) excess through measurement of serum IGF1 levels or an oral glucose tolerance test with GH levels. When acromegaly is suspected based on clinical features, this test is the appropriate first diagnostic step [ 1 ]. During the evaluation, serum IGF1 levels are measured, and if elevated, it supports a diagnosis of GH excess. Alternatively, an oral glucose tolerance test can be used, where the patient receives an oral glucose load, and GH levels are measured over time. In normal individuals, glucose suppresses GH secretion, but in acromegaly, GH levels fail to suppress appropriately due to autonomous secretion from a pituitary adenoma [ 1 ].
Key Points to Consider:
- Elevated serum IGF1 concentration is a reliable marker for GH excess, but its interpretation should consider factors like age, sex, Tanner stage, and potential confounding conditions such as hypothyroidism, malnutrition, or severe infection [ 1 ].
- An oral glucose load test can help confirm the diagnosis by demonstrating the failure of GH levels to suppress below 1 μg/l, although this criterion may be challenging to interpret in adolescents due to physiological variations in GH secretion during puberty [ 1 ].
- After biochemical confirmation of GH excess, imaging studies like MRI can be used to locate and characterize the pituitary tumor, and dynamic pituitary assessment may be offered to evaluate possible hypofunction and hyperfunction of other anterior pituitary hormones [ 1 ].
- Visual field testing and CT scans are important in the evaluation of complications or when MRI is contraindicated but are not the initial diagnostic tests for acromegaly.
- Establishing the biochemical diagnosis with GH testing provides objective evidence of the disease before committing to more expensive or invasive procedures, aligning with the principles of efficient and effective diagnostic pathways [ 1 ].
From the Research
Initial Test for Acromegaly
The initial test for acromegaly is typically focused on assessing the levels of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in the blood.
- The most commonly used initial test is the oral glucose tolerance test (OGTT), which measures the suppression of GH after glucose ingestion 2, 3, 4, 5, 6.
- During the OGTT, blood samples are drawn at various time points after glucose administration to measure GH levels 3, 5.
- A GH level ≥ 1 µg/L after OGTT is often used as a diagnostic criterion for acromegaly 2, 3, 6.
- However, it is essential to note that normal GH suppression after OGTT does not entirely exclude acromegaly, and some patients may have mild or no clinical presentation of the disease 2.
Other Diagnostic Considerations
- IGF-1 levels are also a crucial factor in the diagnosis and monitoring of acromegaly, as they are often elevated in patients with the condition 4, 5, 6.
- Basal serum GH values can be useful in the diagnosis, but they are not as sensitive as OGTT or IGF-1 measurements 6.
- The diagnosis of acromegaly should be based on a combination of clinical features, biochemical tests, and imaging studies, rather than relying on a single test result 6.