What is the initial test for Acromegaly, a condition characterized by excess Growth Hormone (GH) production?

From the Guidelines

The initial test for diagnosing acromegaly should be an assessment of serum IGF1 levels, as elevated levels in relation to age-adjusted, sex-adjusted, and Tanner stage-matched normal ranges support a diagnosis of GH excess 1. When suspecting acromegaly based on clinical features, measuring serum IGF1 is the preferred initial step. This approach is based on the strong recommendation and moderate-quality evidence from the consensus guideline for the diagnosis and management of pituitary adenomas in childhood and adolescence 1.

Key Points to Consider:

• Elevated serum IGF1 concentration is a reliable marker for GH excess, but its interpretation requires consideration of factors such as age, sex, Tanner stage, and potential confounding conditions like hypothyroidism, malnutrition, or severe infection 1.
• An oral glucose load test can be considered to assess the suppression of GH levels, but the interpretation of GH nadir values must take into account the patient's pubertal stage and sex, as normal adolescents may not completely suppress GH levels after a glucose load 1.
• The diagnosis of GH excess should be made within the context of a clinical assessment that includes height velocity, pubertal stage, and bone age, as an elevated serum IGF1 concentration with normal serum GH values might reflect early disease 1.

Diagnostic Approach:

• Measure serum IGF1 levels as the initial test for diagnosing acromegaly.
• Consider an oral glucose load test to assess GH suppression, interpreting results with caution in adolescents.
• Interpret biochemical results within the context of a comprehensive clinical assessment.
• Further investigations, such as dynamic pituitary assessment and imaging studies (e.g., MRI), should be guided by the results of initial biochemical tests and clinical evaluation 1.

From the Research

Initial Test for Acromegaly

The initial test for Acromegaly, a condition characterized by excess Growth Hormone (GH) production, involves several biochemical assessments.

• The oral glucose tolerance test (OGTT) is a key diagnostic tool, as it measures the suppression of GH levels after glucose ingestion 2, 3, 4, 5, 6.
• During the OGTT, a patient's GH levels are measured after consuming a glucose solution, and the results are compared to normal reference intervals 2.
• A GH level of <1 μg/L after OGTT is often used as a cutoff to exclude acromegaly, but this value may not be reliable in all cases 4, 5.
• Insulin-like growth factor-1 (IGF-1) levels are also an important diagnostic marker, as they correlate with clinical features of acromegaly and 24-hour mean GH levels 3, 4, 5.

Limitations of OGTT

While the OGTT is a useful diagnostic tool, it has some limitations.

• Some patients with acromegaly may have normal GH suppression after OGTT, making it essential to consider other diagnostic markers, such as IGF-1 levels 5, 6.
• The suppressibility of GH by glucose in acromegaly is a function of the degree of GH hypersecretion, and OGTT may have limited diagnostic value in patients with mildly increased GH output 6.

Diagnostic Approach

A comprehensive diagnostic approach for acromegaly should include:

• Measurement of IGF-1 levels, which are useful for diagnosing and monitoring the condition 3, 4, 5.
• Basal serum GH levels, which can help diagnose and manage acromegaly 3, 4.
• Nadir GH after OGTT, which provides evidence of the presence or absence of functional autonomy of somatotrope cells 4.