Discordance between mass spectrometry and immunometric IGF-1 assay in pituitary disease: a prospective study
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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.
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.
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.
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.
KeywordsInsulin-like growth factor Pituitary disease Mass spectrometry Immunoassay
The authors thank Dr. Michael P. Caulfield (Quest Diagnostics) for edits and manuscript discussion and Ms. Shira Berman (Cedars-Sinai Medical Center) for manuscript preparation.
Compliance with ethical standards
Conflict of interest
Vivien Bonert declares that she has no conflict of interest. John Carmichael declares that he has no conflict of interest. Zengru Wu is an employee of Quest Diagnostics, Inc. James Mirocha declares that he has no conflict of interest. Daniel Perez declares that he has no conflict of interest. Nigel Clarke is an employee of Quest Diagnostics, Inc. Richard Reitz is an employee of Quest Diagnostics, Inc. Michael McPhaul is an employee of Quest Diagnostics, Inc. Adam Mamelak declares that he has no conflict of interest.
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