Method Validation and Establishment of Reference Intervals for an Insulin-like Growth Factor-1 Chemiluminescent Immunoassay in Cats.

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.

Cat alpha-1-acid glycoprotein enzyme-linked immunosorbent assay: performance characteristics and reference intervals.

OBJECTIVES: The aim of this study was to evaluate performance of a feline-specific ELISA for the measurement of alpha-1-acid glycoprotein (AGP) and to establish a reference interval (RI). METHODS: Surplus serum samples with low (~200 µg/ml), medium (~450 µg/ml) and high (~745 and 930 µg/ml) AGP concentrations were used to assess the intra- and inter-assay coefficients of variation (CVs). The quality goal for bioanalytical method validation was a CV of <20%. Linearity was assessed by serial dilution of a sample with a high AGP concentration. Spike recovery was evaluated by mixing samples with low, medium and high AGP concentrations at different ratios. To establish the RI, residual serum samples from 51 healthy adult cats that were presented for health examinations or blood donation between August 2020 and June 2021 were included. RESULTS: The intra-assay CV was 8.5%, 4.3% and 4.0%, and the inter-assay CV was 18.8%, 15.5% and 11.5% for serum samples with low, medium and high AGP concentrations, respectively. Excellent linearity (R2 = 0.98) was demonstrated for AGP concentrations ranging between 251.6 and 954.4 µg/ml. Average recovery was 95.0-99.7%. The right-sided RI for AGP was 328 µg/ml (90% confidence interval 300-354). Age had a statistically significant impact (increasing values with older age, P = 0.0026), but sex did not (P = 0.44), on AGP concentrations. CONCLUSIONS AND RELEVANCE: The ELISA was accurate and showed acceptable precision with the modification of dilution used in this study. AGP concentrations in this population appeared to increase with increasing age.

Imaging findings in a minipig with congenital portosystemic shunt.

A 15-month-old, male minipig was presented with a clinical history of seizure activity for one year. The minipig was the smallest among the littermates and was referred due to an elevated blood ammonia level with suspected portosystemic shunt (PSS). Ultrasound and CT angiography were consistent with a congenital extrahepatic PSS. To the author's knowledge, this is the first description of a congenital extrahepatic PSS diagnosed by ultrasound and contrast-enhanced computed tomography in a minipig (pig). Partial shunt closure was performed by interventional stent application.