Discordance between mass spectrometry and immunometric IGF-1 assay in pituitary disease: a prospective study.

Abstract

PURPOSE:

Measuring IGF-1, a biomarker for GH activity, is critical to evaluating disordered hypothalamic-pituitary GH axis. Inconsistent IGF-1 measurements among different immunoassays are well documented. We switched from Immulite 2000 immunoassay to narrow-mass-extraction, high-resolution liquid chromatography mass-spectrometry (LC-MS) compliant with recent consensus recommendations on assay standardization. Comparability of these two assays in patients with pituitary disease in a clinical practice setting is not known. We sought to compare IGF-1 levels on Immulite 2000 and LC-MS in samples from naïve and treated patients with secretory and non-secretory pituitary masses.

METHODS:

We prospectively collected serum samples from 101 patients treated at the Cedars-Sinai Pituitary Center between February 2012 and March 2014. We intentionally recruited more patients with acromegaly or GH deficiency to ensure a clinically representative cohort. Samples were classified as in or out of the respective reference ranges. Bland-Altman analysis was used to assess agreement between assays.

RESULTS:

Twenty-four percent of samples were classified differently as below, in, or above range. Agreement between the assays was poor overall, with a significant bias for immunoassay reporting higher values than LC-MS. This pattern was also observed in patients with acromegaly and those with ≥ 2 pituitary hormone deficiencies.

CONCLUSIONS:

IGF-1 results may differ after switching from an older immunoassay to a consensus-compliant assay such as LC-MS. Clinicians should consider the potential impact of assay switching before altering treatment due to discrepant results, particularly in patients monitored over time, such as those with acromegaly and GH deficiency.

• Authors: Vivien Bonert, John Carmichael, Zengru Wu, James Mirocha, Daniel A Perez, Nigel J Clarke, Richard E Reitz, Michael J McPhaul, Adam Mamelak
• Journal: Pituitary (Pituitary) Vol. 21 Issue 1 Pg. 65-75 (Feb 2018) ISSN: 1573-7403 [Electronic] United States
• PMID: 29218459 (Publication Type: Comparative Study, Journal Article)

Chemical References

• Biomarkers
• IGF1 protein, human
• Insulin-Like Growth Factor I

Topics

• Acromegaly (blood, diagnosis)
• Adult
• Aged
• Aged, 80 and over
• Biomarkers (blood)
• Calibration
• Chromatography, High Pressure Liquid (standards)
• Female
• Humans
• Immunoassay (standards)
• Insulin-Like Growth Factor I (analysis)
• Los Angeles
• Male
• Mass Spectrometry (standards)
• Middle Aged
• Pituitary Diseases (blood, diagnosis)
• Pituitary Neoplasms (blood, diagnosis)
• Predictive Value of Tests
• Prospective Studies
• Reference Standards
• Reproducibility of Results
• Young Adult