Abstract
BackgroundInsulin-like growth factor I (IGF-I) measurements are used in veterinary medicine for diagnosing growth hormone disorders. IGF-I assays are subject to interference by IGF-binding proteins (IGFBP) which may not be efficiently removed by standard extraction methods. Adding excess IGF-II during analysis may improve accuracy.
ObjectivesThe purpose of the study was to validate a commercial human IGF-I ELISA which uses excess IGF-II for feline samples and to evaluate biologic variation.
MethodsPrecision was determined by calculating the coefficient of variation (CV). Accuracy was determined by recovery after removal of IGFBP, addition of IGF-I, and linear dilution after the addition of IGFBP. Biologic variation was determined by repeated sampling in 7 cats.
ResultsThere was interference by IGFBP in the high measuring range, resulting in falsely low IGF-I concentrations. This was overcome by the addition of high concentrations of IGF-II. Untreated serum had a measured/expected ratio of 98–115% compared to serum where IGFBP had been removed. Recovery after the addition of IGF-I was 83–112%. Inter- and intra-assay CVs ranged from 2.4% to 5.0% which is within the minimum acceptance criteria based on biologic variation. The reference interval of IGF-I was wide (90–1207 ng/mL) and there was a significant association between body weight and ln IGF-I (P < .000001).
ConclusionsThis human ELISA is suitable for feline samples, but interfering IGFBP can cause falsely low concentrations. It is recommended to dilute samples such that IGF-I is < 28 ng/mL on the standard curve to grant for sufficient IGF-II for binding of interferent IGFBP.
ObjectivesThe purpose of the study was to validate a commercial human IGF-I ELISA which uses excess IGF-II for feline samples and to evaluate biologic variation.
MethodsPrecision was determined by calculating the coefficient of variation (CV). Accuracy was determined by recovery after removal of IGFBP, addition of IGF-I, and linear dilution after the addition of IGFBP. Biologic variation was determined by repeated sampling in 7 cats.
ResultsThere was interference by IGFBP in the high measuring range, resulting in falsely low IGF-I concentrations. This was overcome by the addition of high concentrations of IGF-II. Untreated serum had a measured/expected ratio of 98–115% compared to serum where IGFBP had been removed. Recovery after the addition of IGF-I was 83–112%. Inter- and intra-assay CVs ranged from 2.4% to 5.0% which is within the minimum acceptance criteria based on biologic variation. The reference interval of IGF-I was wide (90–1207 ng/mL) and there was a significant association between body weight and ln IGF-I (P < .000001).
ConclusionsThis human ELISA is suitable for feline samples, but interfering IGFBP can cause falsely low concentrations. It is recommended to dilute samples such that IGF-I is < 28 ng/mL on the standard curve to grant for sufficient IGF-II for binding of interferent IGFBP.
| Original language | English |
|---|---|
| Pages (from-to) | 542-551 |
| Number of pages | 10 |
| Journal | Journal of Veterinary Clinical Pathology |
| Volume | 44 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - 2015 |
Keywords
- growth hormone disorders
- insulin-like growth factor-binding proteins
- size-exclusion chromatography
