CONTEXT: IGF-1 measurements are used for screening and monitoring GH deficiency (GHD) and acromegaly.OBJECTIVE: Our objective was to study whether the introduction of the IDS-iSYS IGF-1 assay would lead to different clinical interpretations in GHD and acromegaly.DESIGN: In 106 GHD subjects and in 15 acromegalic subjects visiting our university hospital, total IGF-1 levels were measured before and during therapy by using the Immulite (IM) assay and IDS-iSYS (ID) assay. Z-scores were calculated by using assay-specific age-specific normative range values. All treatment decisions were based upon results obtained by the IM assay.RESULTS: In GHD subjects, absolute IGF-1 concentrations differed significantly between both IGF-1 assays before treatment (P < .001) but not during GH treatment (P = .32), and mean Z-scores for IGF-1 differed significantly before starting (IM, -2.23, vs ID, -1.43; P < .001) and during GH treatment (IM, -0.60, vs ID, +0.21; P < .001). In acromegalic subjects, absolute IGF-1 concentrations did not differ between both IGF-1 assays before treatment (P = .18) but were significantly different during treatment (P = 0.009), and mean Z-scores for IGF-1 were not different before starting (IM, 10.93, vs ID, 10.78; P = .41) or during treatment (IM, 3.60, vs ID, 3.18; P = .23).CONCLUSIONS: In GHD subjects, mean IGF-1 Z-scores significantly differed when measured by the IM assay compared with the ID assay irrespective of treatment. In contrast, in acromegaly, mean IGF-1 Z-scores did not differ significantly between both assays. Our study suggests that replacement of the IM assay by the ID assay may have far-reaching consequences for the clinical diagnosis and treatment of GHD.

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Persistent URL dx.doi.org/10.1210/jc.2014-2558, hdl.handle.net/1765/91589
Journal Journal of Clinical Endocrinology and Metabolism
Citation
Varewijck, A.J, Lamberts, S.W.J, van der Lely, A-J, Neggers, S.J.C.M.M, Hofland, L.J, & Janssen, J.A.M.J.L. (2015). The introduction of the IDS-iSYS total IGF-1 assay may have far-reaching consequences for diagnosis and treatment of GH deficiency. Journal of Clinical Endocrinology and Metabolism, 100(1), 309–316. doi:10.1210/jc.2014-2558