What blood tests should be ordered to screen for acromegaly?

Blood Work to Screen for Acromegaly

Measure serum IGF-I (insulin-like growth factor-I) as the initial and primary screening test for suspected acromegaly. 1

Initial Screening Test

• Serum IGF-I is the cornerstone screening test and should be the first blood test ordered when acromegaly is suspected 1, 2
• An elevated IGF-I level above the age- and sex-specific normal range is sufficient to establish the diagnosis in the majority of clinically suspected cases 1, 3
• IGF-I was elevated in all patients with acromegaly prior to therapy, making it highly sensitive for screening 3

Confirmatory Testing

If IGF-I is elevated, proceed with:

• Oral glucose tolerance test (OGTT) with growth hormone (GH) measurement is the gold standard confirmatory test 1
• Failure to suppress GH to <1 μg/L during OGTT confirms acromegaly when using modern sensitive assays 1
• With ultrasensitive assays, the cutoff for GH suppression may be as low as 0.4 μg/L 1, 2

Critical Interpretation Factors

IGF-I results must be interpreted using age-, sex-, and Tanner stage-specific reference ranges (in adolescents) to avoid false positives or negatives 1

Factors that can cause falsely normal or low IGF-I despite acromegaly:

• Severe hypothyroidism 1
• Malnutrition or severe infection 1

Factors that can cause falsely elevated IGF-I without acromegaly:

• Hepatic and/or renal insufficiency 1

When OGTT is Most Useful

The OGTT provides corroborative evidence particularly when:

• IGF-I elevation is modest (less than twice the upper limit of normal) 3
• Clinical features are absent or equivocal 3
• There is discordance between clinical suspicion and IGF-I levels 2

Common Pitfall to Avoid

Do NOT use OGTT with GH suppression for monitoring patients already on medical treatment – results are inconsistent and unreliable in this setting 1. For follow-up, rely on IGF-I levels alone.

Why This Matters for Patient Outcomes

• Elevated GH and IGF-I levels are direct predictors of mortality in acromegaly 1, 4
• Normalizing these levels through treatment reduces mortality to rates similar to the general population 1, 4
• Early diagnosis is critical because untreated acromegaly leads to heart failure (the most common cause of death), cerebrovascular disease, and increased colorectal cancer risk 4, 5