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Method Validation and Establishment of Reference Intervals for an Insulin-like Growth Factor-1 Chemiluminescent
Arne Güssow1, Sabine Thalmeier1, Ruth Gostelow2
1Clinic for Small Animals (Internal Medicine, Clinical Pathology and Clinical Pathophysiology), Justus-Liebig-University, 35392 Giessen, Germany.
Insights
A new chemiluminescent immunoassay (CLIA) accurately measures feline insulin-like growth factor-1 (IGF-1), offering a safer alternative to RIA for diagnosing hypersomatotropism (HS) in diabetic cats.
Area of Science:
- Veterinary diagnostics
- Endocrinology
- Assay validation
Background:
- Radioimmunoassay (RIA) for insulin-like growth factor-1 (IGF-1) is the sole method for diagnosing feline hypersomatotropism (HS).
- Limitations of IGF-1 RIA include radiation hazards, limited availability, and high costs, necessitating alternative diagnostic methods.
- Automated analyzers require validated assays, such as chemiluminescent immunoassay (CLIA), for routine clinical use.
Purpose of the Study:
- To validate a CLIA for feline IGF-1 measurement.
- To compare CLIA performance against the established IGF-1 RIA method.
- To establish a reference interval (RI) and diagnostic cut-off for HS in diabetic cats.
Main Methods:
- Assay validation included precision, linearity, and recovery studies for the CLIA.
- A reference interval (RI) was determined using serum from 50 healthy adult cats.
- Method comparison involved 68 diabetic cat serum samples, analyzed by both CLIA and RIA, with ROC analysis for cut-off determination.
Main Results:
- The CLIA demonstrated excellent precision (intra-assay CV ≤4.7%, inter-assay CV ≤5.6%) and linearity (R² > 0.99).
- A very high correlation (rs = 0.97) was observed between CLIA and RIA, with a mean bias of -24.5% for CLIA.
- The established RI upper limit was 670 ng/mL, and the optimal HS diagnostic cut-off was 746 ng/mL (Sensitivity 84.4%, Specificity 97.2%).
Conclusions:
- The validated CLIA exhibits good performance characteristics for feline IGF-1 measurement.
- The established RI and HS diagnostic cut-off enable the use of CLIA in routine veterinary diagnostics.
- CLIA provides a viable, non-radioactive alternative for diagnosing hypersomatotropism in diabetic cats.
Abstract:
Previously, radioimmunoassay (RIA) has been the only assay to measure insulin-like growth factor-1 (IGF-1) to diagnose hypersomatotropism (HS). Due to radiation concerns, availability, and the cost of IGF-1 RIA, validation of assays for automated analysers such as a chemiluminescent immunoassay (CLIA) is needed. The aim of this study was to validate a CLIA for measurement of feline IGF-1 (IMMULITE 2000® XPi, Siemens Medical Solutions Diagnostics, Malvern, PA, USA) compared to IGF1 RIA, establish reference interval (RI), and determine a cut-off value for diagnosis of HS in diabetic cats. Validation of assay performance included precision, linearity, and recovery studies. Right-sided RI was determined using surplus serum of 50 healthy adult cats. Surplus serum samples of diabetic cats with known IGF-1 concentration with (n = 32/68) and without HS (n = 36/68) were used for method comparison with RIA. The cut-off for diagnosis of HS was established using receiver operating characteristic (ROC) analysis. The intra-assay coefficient of variation (CV) was ≤4.7%, and the inter-assay CV was ≤5.6% for samples with low, medium, and high IGF-1 concentration. Linearity was excellent (R2 > 0.99). The correlation between CLIA and RIA was very high (rs = 0.97), with a mean negative bias for CLIA of 24.5%. The upper limit of RI was 670 ng/mL. ROC analysis showed an area under the curve of 0.94, with best cut-off for diagnosis of HS at 746 ng/mL (sensitivity, 84.4%; specificity, 97.2%). The performance of CLIA was good, and the RI and cut-off for HS diagnosis established in this study allow for CLIA to be used in routine work-up of diabetic cats.
