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Assay-dependent results of immunoassayable spontaneous 24-hour growth hormone secretion in short children
M L Granada1, A Sanmartí, A Lucas
1Laboratorio Hormonal y Sección de Endocrinología, Hospital Germans Trías i Pujol, Badalona, Universidad Autónoma de Barcelona, Spain.
Insights
Commercial immunoassays show significant variability in measuring growth hormone (GH) levels in children with short stature. Assay choice greatly impacts GH results, affecting clinical interpretation and diagnosis.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Pediatric Endocrinology
Background:
- Accurate measurement of growth hormone (GH) is crucial for diagnosing short stature in children.
- Numerous commercial immunoassays exist for GH quantification, but their comparability is not well-established.
- Variability in assay performance can lead to misinterpretation of GH secretion studies.
Purpose of the Study:
- To evaluate the performance and comparability of various commercial immunoassays for measuring 24-hour spontaneous growth hormone secretion in children.
- To assess the impact of different immunoassay types (polyclonal vs. monoclonal, RIA vs. IRMA) on GH level determination.
Main Methods:
- Collected 24-hour spontaneous growth hormone (GH) secretion samples from 48 children with short stature.
- Assessed GH levels using up to 11 different commercial immunoassays, including radioimmunoassays (RIA) and immunoradiometric assays (IRMA).
- Compared mean GH values from various assays against reference polyclonal RIA methods and analyzed inter-assay ratios.
Main Results:
- Significant variability was observed in GH measurements across different commercial immunoassays, with some assays yielding results up to three times higher than others.
- Monoclonal immunoradiometric assays (IRMAs) showed particularly wide variations in GH quantification.
- While ratios between two polyclonal assays remained relatively constant for individual children, significant inter-child variations were noted.
Conclusions:
- The choice of immunoassay significantly impacts the measured growth hormone levels in 24-hour secretion studies.
- Clinical interpretation of short stature diagnoses based on GH levels requires careful consideration of the specific assay used.
- Further standardization of GH immunoassays is needed to ensure reliable and comparable diagnostic results.
Abstract:
Forty-eight children, referred for evaluation of short stature, underwent 24-hour spontaneous growth hormone (GH) secretion studies. The GH level in pooled sera was assessed for each child, using up to 11 commercial immunoassays. In a group of 15 children, the mean GH values obtained by nine of the assays were compared with the mean value given by a polyclonal radioimmunoassay (RIA) from Sorin: four gave higher results (p less than 0.0001), three gave comparable results and two gave lower results (p less than 0.001). The assay yielding the highest results (Nichols: 5.9 +/- 2.3 ng/ml, mean +/- SD) gave values that were approximately triple those obtained by the assay yielding the lowest results (Hybritech: 1.8 +/- 0.8 ng/ml; p less than 0.0001); both of these are monoclonal immunoradiometric assays (IRMAs). The GH concentrations measured in 24-hour pools from 32 children using a monoclonal IRMA from Biomérieux were similar to those obtained using a polyclonal RIA from Farmos (2.8 +/- 1.1 ng/ml and 2.9 +/- 1.4 ng/ml, respectively) but significantly lower than those measured by another polyclonal RIA from Sorin (3.5 +/- 1.5 ng/ml). Two polyclonal assays (Biomérieux and Sorin) were then used to measure the GH levels in all of the 30-minute samples and in the day, night and 24-hour pools from the secretion studies of 22 children. The ratio of the results of the two assays remained fairly constant for a given child (although the GH levels in different 30-minute samples differed considerably). However, the ratios between different children showed quite wide variation (from 2.03 to 1.04).(ABSTRACT TRUNCATED AT 250 WORDS)