Insulin-like growth factor I in XXXX : validation of an enzyme-linked immunosorbent assay and determination of biologic variation.

@entity1 @entity468 @entity442 @entity5100
BACKGROUND: Insulin-like growth factor I ( @entity442 ) measurements are used in veterinary medicine for diagnosing growth hormone disorders. @entity442 assays are subject to interference by IGF-binding proteins (IGFBP) which may not be efficiently removed by standard extraction methods. Adding excess @entity5100 during analysis may improve accuracy. OBJECTIVES: The purpose of the study was to validate a commercial @entity1 @entity442 ELISA which uses excess @entity5100 for feline samples and to evaluate biologic variation. METHODS: Precision was determined by calculating the coefficient of variation (CV). Accuracy was determined by recovery after removal of IGFBP, addition of @entity442 , and linear dilution after the addition of IGFBP. Biologic variation was determined by repeated sampling in 7 @entity468 . RESULTS: There was interference by IGFBP in the high measuring range, resulting in falsely low @entity442 concentrations. This was overcome by the addition of high concentrations of @entity5100 . Untreated serum had a measured/expected ratio of 98-115% compared to serum where IGFBP had been removed. Recovery after the addition of @entity442 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 @entity442 was wide (90-1207  ng/mL) and there was a significant association between body weight and ln  @entity442 (P  <  .000001). CONCLUSIONS: This @entity1 ELISA is suitable for feline samples, but interfering IGFBP can cause falsely low concentrations. It is recommended to dilute samples such that @entity442 is <  28  ng/mL on the standard curve to grant for sufficient @entity5100 for binding of interferent IGFBP.
