Development and analytical validation of a radioimmunoassay for the measurement of alpha1-proteinase inhibitor concentrations in feces from healthy puppies and adult dogs

Abstract

Canine α₁-proteinase inhibitor (cα₁-PI), a proteolysis-resistant protein with a molecular weight similar to albumin, has been shown to be clinically useful as a marker for gastrointestinal protein loss in dogs. A competitive, liquid-phase radioimmunoassay was developed and analytically validated. Fecal samples were collected from 101 healthy pet dogs of various breeds and ages, and fecal cα₁-PI (Fcα₁-PI) concentrations were compared between dogs of different age groups. A reference interval for Fcα₁-PI concentration was calculated using the central 95th percentile. Analytical sensitivity of the assay was 2.2 µg Fcα₁-PI/g feces. Observed-to-expected ratios for the serial dilution and spiking recovery of 9 and 6 fecal extracts ranged from 90.4 to 152.0% and from 71.3 to 112.3%, respectively. Coefficients of variation for intra- and interassay variability for 6 fecal extracts were ≤10.8% and ≤12.5%, respectively. The reference intervals for the mean and maximum Fcα₁-PI from fecal samples collected on 3 consecutive days were 2.2–13.9 µg/g and 2.2–21.0 µg/g, respectively. Fcα₁-PI was significantly higher in dogs 1-PI for the 3 samples). The radioimmunoassay described is sensitive, linear, precise, reproducible, and accurate for clinical use, thus allowing reliable quantification of Fcα₁-PI in clinical patients. Using this assay, a mean or a maximum Fcα₁-PI for 3 sampling days of >13.9 µg/g or >21.0 µg/g, respectively, should be considered abnormal in dogs >1 year of age. Fecal cα₁-PI concentrations in dogs <1 year of age were significantly higher and should be carefully interpreted in this age group.