Endocrine Abstracts

Introduction: IGF-I is a clinically relevant protein in the diagnosis and monitoring of treatment of growth disorders. The Growth Hormone Research Society and the International IGF Research Society have encouraged the adoption of a universal calibration for immunoassays to improve standardization of IGF-I measurements.

Objectives: Comparison of new standardization IGF-I assay with IGF-I assay currently used in CHLC, Lisbon; To study whether the introduction of the new assay would lead to different clinical interpretations, verifying the concordance of results.

Material and Methods: A random sample of 186 patients regularly assisted at CHLC, mostly in Endocrinology Departments, comprising both genders, ages 2 months–85 years. Determinations on IMMULITE 2000 (Siemens). Chemiluminescent assays: new standardization (1st IS WHO, 02/254 NIBSC) and old (1st IRR WHO, 87/518 NIBSC); An Excel tool was used for statistical treatment. For comparison statistics we excluded 9 patients.

Results: Comparison statistics: r=0.994; Slope=0.63; interception (ng/ml)=22.4; n=177; range 27.2–938.0 ng/ml. According to assay and age-specific reference values specified by the manufacturer, we found concordance between 78.3 and 90.4%, regardless of gender, with the exception of 0–3 year age group, in which concordance fell below 33.3 and 50%.

Conclusions: Comparison statistics revealed data overlapping with those of the manufacturer. Although there was a good agreement between assays results, caution should be exercised in the interpretation of a single IGF-I value and of the impact of the new standardization. Discrepancies require posterior evaluation in the evolution of the disease, mainly in group 0–3 years. Clinicians should be aware of the tendency to reduce IGF-I values with the new calibration, so that they do not attribute it to a change in patient status.