Acromegaly Biochemical Diagnosis (IGF-1 + OGTT)

What the result means

Confirmatory

IGF-1 above 1.3 times the age- and sex-matched upper limit of normal, together with typical clinical features.

Excluded

A normal age- and sex-matched IGF-1 WITH a suppressed growth hormone nadir on the 75 g oral glucose tolerance test.

The assay decides

The nadir threshold is below 1.0 micrograms/L on a conventional assay and below 0.4 on an ultrasensitive one. One figure used for both gets one of them wrong.

Random GH

Not a diagnostic test. Growth hormone is secreted episodically, and the guideline recommends against single random measurements.

What a random can do

Contribute to EXCLUSION only, and only below 0.4 micrograms/L alongside a normal IGF-1. A raised random level supports nothing on its own.

Both halves

Exclusion needs both. A suppressed nadir with a raised IGF-1 does not exclude acromegaly, and a normal IGF-1 with an unsuppressed nadir does not establish it.

Discordance

A result in its own right, calling for further evaluation rather than a verdict.

Age-matched or useless

IGF-1 falls with age, so a laboratory range that is not age- and sex-specific cannot answer this question at all.