Evaluation of three different point-of-care tests for quantitative measurement of canine C-reactive protein.

BACKGROUND: C-reactive protein (CRP) is a major acute phase protein in both people and dogs. OBJECTIVE: The objective of this study was to evaluate the precision and accuracy of 3 different point-of-care tests (POCT) for canine CRP (cCRP) in comparison to a standard ELISA test, and to assess storage stability. MATERIAL AND METHODS: Blood samples were collected from 125 dogs (23 healthy and 102 diseased). Serum cCRP measurements were performed using the TECOmedical AG, the EUROLyser Diagnostica, and the LifeAssays POCT. The TECOmedical AG ELISA validated for canine serum was used as a reference method. Statistical analyses included descriptive statistics, inter assay variance for each POCT, comparison of results from each POCT with the ELISA using Spearman's correlation and Bland-Altman plots, and a t-test to evaluate sample stability. RESULTS: ELISA cCRP values ranged from 0.1-4.7 mg/L (median 1.3) in healthy dogs and from 0-282 mg/L (median 17.3) in diseased dogs. Spearman's correlation coefficient between ELISA and the respective POCT measurements for cCRP concentration was 0.89 for TECOmedical, 0.85 for EUROLyser, and 0.97 for LifeAssays. Bias calculated from Bland-Altman difference plots was 27.6% for TECOmedical, -14.2% for EUROLyser, and -15.7% for LifeAssays. Inter assay reliability was > 0.9 for all POCT. Total observed error of the EUROLyser was 28.2% and therefore met the acceptable total error of 29.6%. CONCLUSIONS: All POCTs were able to measure cCRP, but precision, accuracy, and correlation coefficients varied among the 3 systems. Therefore, serial measurements for monitoring of cCRP in dogs should always be performed using the same POCT system.

Differentiating between analytical and diagnostic performance evaluation with a focus on the method comparison study and identification of bias.

Prior to introduction of a new method to the diagnostic laboratory, analytical performance must be validated to ensure operation within the manufacturer's specifications and/or within predetermined quality requirements. In addition, the new method may require diagnostic performance assessment to ensure it differentiates between diseased and nondiseased individuals as intended. These 2 phases of assessment, while complementary, are not equivalent and require a different set of experiments, statistical analyses, and interpretation. Studies of analytical performance typically include a method comparison experiment, the purpose of which is to identify bias (inaccuracy) of the "test" (or "index") method (new method) relative to a "comparative method" (established method). Analysis of method comparison data is facilitated by commercial software programs that present the statistical significance of identified bias; however, the clinical relevance of any bias also should be considered. Studies of diagnostic performance should not be pursued until analytical performance is fully characterized and may not be required for well-established tests or for those for which results are nonspecific (ie, not referable to a specific disease or condition). Diagnostic performance assessment may include assessment of sensitivity, specificity, predictive values, odds ratios, and/or likelihood ratios. The purpose of this review is to clarify differences between the assessment of analytical and diagnostic performance, and to explore the method comparison study and bias assessment from a perspective not addressed in prior veterinary articles.

Evaluation of three automated human immunoturbidimetric assays for the detection of C-reactive protein in dogs.

C-reactive protein (CRP) is a major, acute-phase protein in dogs; however, there is a need for automated assays to ensure in-time patient monitoring. Three automated immunoturbidimetric assays (Randox, Thermo, and Wako) developed for human beings were evaluated for their ability to detect canine CRP, including method validation, evaluation of diagnostic use, and establishment of exploratory reference intervals. Sera from 36 healthy dogs and 82 diseased dogs were included for method comparison with the enzyme-linked immunosorbent assay (ELISA; Tridelta) serving as the reference method. A nonparametric estimate of the 1-sided 95% reference interval was established (n = 36). Precision study revealed good intra-assay coefficients of variation (CVs) of 1-10%, 0-9%, and 2-13% for the Randox, Thermo, and Wako assays, respectively. Interassay CVs were 18%, 24%, and 19% respectively. Because of a low linear range, the Thermo test was considered unsuitable for use with canine specimens. No significant differences were present between the results obtained with the Randox and Wako assays with CRP concentrations less than 15 mg/l; however, median CRP results differed significantly between the Thermo test and the ELISA (P = 0.03). Bland-Altman analysis detected a proportional bias of 0.28, -0.59, and 0.61 mg/l for the Randox, Thermo, and Wako assays, respectively. For all tests, median CRP values were significantly different between healthy dogs and dogs with neoplasia. The upper limit of the reference intervals were 8.2 and 9.9 mg/l for the Randox and Wako assays, respectively. In contrast to the Thermo test, the Randox and Wako assays were suitable for detection of abnormally high canine CRP concentrations; however, improvement of assay precision and evaluation of accuracy are warranted before their clinical use with canine specimens.

Estimation of intestinal permeability in healthy dogs using the contrast medium iohexol.

BACKGROUND: Iohexol is a nonradioactive marker that has been used successfully to test intestinal permeability in humans with inflammatory bowel disease. There is evidence in dogs that iohexol shares a similar permeability pathway as (51)chromium-EDTA, the gold standard marker. OBJECTIVE: The objective of this study was to determine an optimal oral iohexol dosage for an intestinal permeability serum test (IPST) and to use the test to estimate intestinal permeability in healthy dogs. METHODS: Eight clinically healthy dogs free of gastrointestinal, liver, and pancreatic disease were used in the study. Dosages of 0.25, 0.5, 1.0, 2.0, and 4.0 mL/kg of Omnipaque-350 (iohexol) were administered to 2 dogs at weekly intervals. Iohexol concentration was determined in serum samples obtained hourly for 6 hours after administration by high-performance liquid chromatography. Using the optimal dosage, iohexol was administered to 8 dogs twice, 6-36 days (mean 10 days) apart, and coefficients of variation (CVs) for iohexol concentration were calculated. RESULTS: A dosage of 2.0 mL/kg was chosen as optimal for the IPST, based on ease of iohexol detection in serum, intestinal contrast, and clinical effects of iohexol. Following administration of this dose to healthy dogs, mean (+/-SD) serum iohexol concentrations were 8.74+/-4.38, 11.89+/-5.67, 12.40+/-5.47, 9.23+/-5.54, 7.61+/-5.13, and 5.27+/-2.67 microg/mL at 1, 2, 3, 4, 5, and 6 hours after iohexol administration, respectively. CVs between the 2 test days were 28-45%. CONCLUSIONS: Using the iohexol dosage established in this study, the iohexol IPST was easy to perform as a marker for intestinal permeability in dogs. Further studies to establish reference intervals and evaluate the diagnostic value of the iohexol IPST in dogs with gastrointestinal disease are warranted.