Varewijck AJ, Lamberts SWJ, van der Lely AJ, Neggers SJCMM, Hofland LJ, Janssen JAMJL. The Introduction of the IDS-iSYS Total IGF-I Assay may have Far-reaching Consequences for Diagnosis and Treatment of GH Deficiency. The Journal of Clinical Endocrinology & Metabolism. http://press.endocrine.org/doi/abs/10.1210/jc.2014-2558
Context: Insulin-like growth factor-I (IGF-I) measurements are used for screening and monitoring GH deficiency (GHD) and acromegaly.
Objective: To study whether the introduction of the IDS-iSYS IGF-I 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-I 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: GHD: 1] Absolute IGF-I concentrations differed significantly between both IGF-I assays before treatment (p<0.001), but not during GH treatment (p= 0.32); 2]. Mean Z-scores for IGF-I differed significantly before starting (IM: -2.23 vs. ID: -1.43 (p<0.001) and during GH treatment (IM: -0.60 vs. ID: +0.21 (p<0.001).
Acromegaly: 1] Absolute IGF-I concentrations did not differ between both IGF-I assays before treatment (p=0.18), but were significantly different during treatment (p= 0.009); 2]. Mean Z-scores for IGF-I were not different before starting (IM: 10.93 vs. ID: 10.78 (p=0.41) or during treatment (IM: 3.60 vs. ID: 3.18 (p=0.23).
Conclusions: In GHD subjects mean IGF-I Z-scores significantly differed when measured by the IM assay compared to the ID assay irrespective of treatment. In contrast, in acromegaly mean IGF-I 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.
Context: Insulin-like growth factor-I (IGF-I) measurements are used for screening and monitoring GH deficiency (GHD) and acromegaly.
Objective: To study whether the introduction of the IDS-iSYS IGF-I 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-I 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: GHD: 1] Absolute IGF-I concentrations differed significantly between both IGF-I assays before treatment (p<0.001), but not during GH treatment (p= 0.32); 2]. Mean Z-scores for IGF-I differed significantly before starting (IM: -2.23 vs. ID: -1.43 (p<0.001) and during GH treatment (IM: -0.60 vs. ID: +0.21 (p<0.001).
Acromegaly: 1] Absolute IGF-I concentrations did not differ between both IGF-I assays before treatment (p=0.18), but were significantly different during treatment (p= 0.009); 2]. Mean Z-scores for IGF-I were not different before starting (IM: 10.93 vs. ID: 10.78 (p=0.41) or during treatment (IM: 3.60 vs. ID: 3.18 (p=0.23).
Conclusions: In GHD subjects mean IGF-I Z-scores significantly differed when measured by the IM assay compared to the ID assay irrespective of treatment. In contrast, in acromegaly mean IGF-I 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.
