# Evaluation of the analytical performance of a point‐of‐care analyzer for the measurement of feline serum thyroxine concentration in comparison with a chemiluminescence enzyme immunoassay

## TL;DR

This study evaluates a portable device for measuring thyroid hormone in cats and compares it to a standard lab method, finding it reliable except for some interference and limited range.

## Contribution

The study provides a detailed validation of a point-of-care analyzer for feline thyroxine measurement and compares it to a reference method.

## Key findings

- The POCA showed excellent analytical performance with ≤4% coefficient of variation and linearity within its dynamic range.
- The POCA correlated well with the reference method (r_s = 0.95) but had a slight proportional bias of 4.5%.
- Hemoglobin interference caused a 28% negative bias, and 15% of samples had discordant thyroid status results.

## Abstract

Total thyroxine (TT4) measurement is used to assess thyroid status in cats.

The aim of the prospective study was to evaluate the analytical performance of the point‐of‐care analyzer (POCA) Immuno AU10V using the v‐T4 test kit for feline TT4 measurement. Additionally, method comparison with a benchtop analyzer (IMMULITE 2000) was done.

Validation included linearity, inter‐ and intra‐assay precision, precision near the lower limit of quantification (LloQ), and interference testing for hemoglobin, lipid, and bilirubin. Correlation and bias were assessed.

Linearity was given within the dynamic range. Coefficients of variation (CV) were ≤4% near the LloQ as well as for intra‐and inter‐assay precision. No interference was observed for lipid and bilirubin, while hemoglobin caused a negative bias of 28%. Method comparison included 74 samples within three TT4 concentration ranges (0.5–3.7, >3.7–5.13, >5.13–8 μg/dL). Correlation between POCA and reference method was excellent (r
s = 0.95) with a slight proportional bias of 4.5%. TEobs was between 7.0% and 9.8%. Despite substantial agreement, discordant results on thyroid status occurred in 15% of samples.

The analytical performance of the POCA was excellent, as was its correlation with the reference method. Except for the interferent effect of hemoglobin, the TEobs was <TEa for all analyses. Analysis of severely hemolytic samples is not advised. However, the relatively small dynamic range of the POCA precludes quantitative analysis of samples with TT4 >8 μg/dL, and de novo reference intervals need to be established.