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      Variation in Growth Hormone Immunoassays in Clinical Practice in Canada

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          Background/Aims: The diagnosis of growth hormone (GH) deficiency in children in Canada is based on clinical, auxological, radiographic and biochemical criteria which include response to provocative GH testing. The objective of this study was to determine the variability of GH assays used at Canadian pediatric hospitals. Methods: Pooled samples of patient sera were generated at a single center and tested at 15 laboratories across Canada using local GH assays. Additional samples were analyzed using the most commonly employed assays. Results: DSL and AutoDelfia<sup>©</sup> assays measured lower for all samples. Linear regression analysis demonstrated excellent correlation between Access 2<sup>©</sup>, AutoDelfia, and Immulite 2000<sup>©</sup>, however, Bland-Altman plots revealed bias when comparing these assays. Conclusions: Adequate comparison and standardization of commercially available GH immunoassays is necessary to ensure consistent interpretation of results.

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          Most cited references 8

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          Consensus Guidelines for the Diagnosis and Treatment of Growth Hormone (GH) Deficiency in Childhood and Adolescence: Summary Statement of the GH Research Society

           G. Society (2000)
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            Effects of sample handling on the stability of interleukin 6, tumour necrosis factor-alpha and leptin.

            Detected levels of IL-6, TNF-alpha and leptin may be affected by methods of storage, anticoagulant or repeated freezing-thawing. Blood samples from 22 healthy subjects were: (i) allowed to stand for 1, 2, 4 or 6 h prior to, or after separation, before freezing at -70 degrees C; (ii) taken into tubes with lithium heparin, sodium citrate, EDTA or no anticoagulant, separated and frozen; and (iii) separated, and plasma repeatedly freeze-thawed for up to six cycles prior to assay. Leptin was assayed by RIA, and IL-6 and TNF-alpha by high-sensitivity ELISA. (i) IL-6 and TNF-alpha levels were not altered significantly in separated samples but IL-6 declined by mean (SEM) 14.3% (3.7%) and TNF-alphaincreased by 9.6% (2.3%) in samples left unseparated for 4 h (P=0.003 and 0.002, respectively). Leptin remained unchanged. (ii) Serum and EDTA-plasma samples gave comparable results for all three cytokines, but levels in the other anticoagulant samples were highly variable. (iii) IL-6 and leptin levels were not altered by up to 6 cycles of freeze-thawing, but TNF-alpha increased by 17.0% (3.7%) after 3 cycles. Concentrations of these molecules are significantly altered by storage conditions, therefore they need to be standardized for epidemiological and clinical studies, and between-study comparisons of levels may not be reliable. Copyright 2000 Academic Press.
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              Variability in the quantitation of circulating growth hormone using commercial immunoassays.

              The quantitation of human GH in a serum sample is not consistent among various commercially available immunoassays. We measured serum GH concentrations with four RIAs [Cambridge, Kallestad, National Hormone and Pituitary Program, and Radioassay Systems Laboratories (RSL)] and two immunoradiometric assays (IRMAs; Hybritech and Nichols). Serum GH concentrations measured by the RIAs were between 1.9 and 2.8 times higher than those determined by the Hybritech IRMA, whereas the concentrations measured by the Nichols IRMA were approximately 3.0 times higher than the Hybritech values. We evaluated the effects of differences in standards, assay diluents, and antibody specificity on GH measurement in the various assays. When GH standards from each of the assays were measured in the Hybritech IRMA, only the RSL standard was less immunoreactive than the other assay standards. Different assay diluents also resulted in varying GH values. In the RIAs, GH diluted in serum was more immunoreactive than GH diluted in phosphate-buffered saline-0.5% BSA. This enhanced immunoreactivity appeared to be due to a nonspecific effect generated by serum. The Nichols and Hybritech IRMAs provide standards diluted in horse serum. In the Nichols assay, GH diluted in human serum was more immunoreactive than GH diluted in horse serum, whereas the immunoreactivity of GH diluted in either serum was equal in the Hybritech IRMA. These IRMAs also differ in that the Nichols assay detected the 20K variant of GH, whereas the Hybritech assay did not. Considering these discrepancies, comparison of data obtained using different assays should be made carefully.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                May 2008
                06 February 2008
                : 69
                : 5
                : 290-294
                aDivision of Endocrinology, Hospital for Sick Children, University of Toronto, Toronto, Ont., and bDepartment of Clinical Chemistry, CHU Sainte Justine, Université de Montréal, Montréal, Que., Canada
                114860 Horm Res 2008;69:290–294
                © 2008 S. Karger AG, Basel

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                Figures: 1, Tables: 1, References: 12, Pages: 5
                Original Paper


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