Elevated insulin-like growth factor-1 in patients without clinical evidence of acromegaly

To (1) identify the frequency of IGF-1 elevation in a cohort of patients without clinically suspected GH excess, in a state-based reference laboratory over a 24-month period, and (2) to examine potential differences in comorbidities and relevant medications between people with an elevated IGF-1 compared to a matched control group.

All IGF-1 measurements at Pathology Queensland between 1/12/2018-1/12/2020 were identified. The medical records of those with IGF-1 ≥1.1x the upper limit of the reference range were appraised to determine: (1) documentation of acromegalic features, (2) relevant comorbidities and medication use, and (3) further investigations to exclude pathological GH excess.

There were 2759 IGF-1 samples measured in 1963 people ≥18 years, over the specified period. Of these, 204 had IGF-1 ≥1.1x the upper limit of the age-matched reference range; 102 cases (61M, 41F) met inclusion criteria, and were matched to 102 controls with a normal IGF-1 based on age, sex, gonadal status and pituitary anatomy on MRI.

There were significant differences in the frequency of dopamine agonist use (19/102 cases vs. 6/102 controls, OR = 3.66, 95% confidence interval [CI]: 1.45-9.29, p = .009) and chronic kidney disease (CKD) (14/102 cases vs. 4/102 controls, OR = 3.90, 95% CI: 1.28-11.14, p = .024).

Out of 1963 patients having IGF-1 measured, 102 (5.2%) had an elevated IGF-1 where there was no known acromegaly, GH replacement or endogenous glucocorticoid excess. Intraindividual biological variability, assay imprecision and physiological factors are known contributors to falsely elevated IGF-1, dopamine agonist therapy and CKD should also be considered.