What are the diagnostic tests for acromegaly (a growth hormone disorder)?

From the Guidelines

Testing for acromegaly should begin with measuring insulin-like growth factor 1 (IGF-1) levels in the blood, as an elevated level in relation to the age-adjusted, sex-adjusted, and Tanner stage-matched normal range is a reliable marker for GH excess 1.

Initial Screening

• The initial screening test for acromegaly is the measurement of IGF-1 levels in the blood, which is a reliable marker for GH excess 1.
• Elevated IGF-1 levels should be interpreted with caution, especially in adolescents during the peak growth spurt, as marginal or mild elevation may not necessarily indicate GH excess 1.
• Local Tanner stage-matched, sex-matched, and age-matched normal ranges for the IGF1 assay must be established to avoid notable inter-assay variability 1.

Confirmatory Testing

• If IGF-1 levels are elevated, the next step is an oral glucose tolerance test (OGTT) where GH levels are measured after consuming a glucose load, with a cut-off of 1 μg/l for GH suppression 1.
• However, complete suppression of GH can be difficult to achieve in normal adolescence, and GH nadir after glucose load in children undergoing puberty is sex and pubertal stage-specific 1.
• An elevated serum IGF1 concentration, with apparently normal serum GH values, might reflect early disease, and biochemical results should be interpreted within a clinical assessment of phenotype that includes height velocity, pubertal stage, and bone age 1.

Imaging and Further Evaluation

• If these tests suggest acromegaly, magnetic resonance imaging (MRI) of the pituitary gland should be performed to identify the likely pituitary adenoma causing excess GH production 1.
• MRI using high-resolution pituitary protocols is generally considered the gold standard for imaging the pituitary gland in cases of suspected hormone-secreting adenoma 1.
• Additional tests may include visual field testing if the tumor is large enough to compress the optic chiasm, and assessment of other pituitary hormones to check for hypopituitarism 1.
• Dynamic pituitary assessment of possible hypofunction and hyperfunction of other anterior pituitary hormones should also be offered to children and adolescents with GH excess 1.

From the Research

Diagnostic Steps for Acromegaly

• The first step in diagnosing acromegaly is recognizing it clinically, which can be challenging due to its insidious nature and non-specific symptoms 2.
• Once suspected clinically, IGF-1 measurement is the initial step in making the biochemical diagnosis 3, 4.
• GH and IGF-1 should be considered in concert, and providers should be aware of conditions that can alter GH and IGF-1 levels and each assay's performance 3.
• The oral glucose tolerance test (OGTT) with concomitant GH measurement is the gold standard diagnostic test for acromegaly 2.

Biochemical Confirmation

• Elevated IGF-1 levels, alone, are sufficient to establish a diagnosis of acromegaly in the majority of clinically suspected cases 4.
• The OGTT may be useful to obtain corroborative evidence when there is modest elevation of IGF-1 with absent or equivocal clinical features 4.
• GH suppression after oral glucose load and normal age- and gender-matched IGF-I levels reflect biochemical control of acromegaly 5.

Imaging and Further Evaluation

• Pituitary magnetic resonance imaging is advised in patients with acromegaly to identify an underlying pituitary adenoma 6.
• Clinical, endocrine, imaging, histologic, and molecular markers may help predict the response to medical therapy 6.