Evaluation of a novel quantitative canine species-specific point-of-care assay for C-reactive protein

Abstract

BackgroundSpecies-specific point-of-care tests (POCT) permit a rapid analysis of canine C-reactive protein (CRP), enabling veterinarians to include CRP in clinical decisions. Aim of the study was to evaluate a novel POCT for canine CRP (Point Strip™ Canine CRP Assay) run on a small in-house-analyzer (Point Reader™ V) using lithium heparin plasma and to compare assay performance to an already established canine CRP assay (Gentian Canine CRP Immunoassay) run on two different bench top analyzers serving as reference methods (ABX Pentra 400, AU 5800).Linearity was assessed by stepwise dilution of plasma samples with high CRP concentrations. Limit of quantification (LoQ) was determined by repeated measurements of samples with low CRP concentrations. Coefficient of variation (CV) at low (10–50 mg/l), moderate (50–100 mg/l), and high (100–200 mg/l) CRP concentrations was investigated as well as possible interferences. Method comparison study was performed using 45 samples of healthy and diseased dogs. Quality criteria were fulfilled if the total observed error (TEobs = 2CV% + bias%) was below the minimal total allowable error of 44.4% (TE min). Additionally, a reference range (n = 60 healthy dogs) was established.ResultsLinearity was present at CRP concentrations of 10–132 mg/l (≙ 361 mg/l CRP with reference method) with a LoQ set at 10 mg/l. At moderate to high CRP concentrations, intra- and inter-assay CVs were ≤ 8% and ≤ 11% respectively, while CVs ≤ 22% and ≤ 28% were present at low concentrations. No interferences were observed at concentrations of 4 g/l hemoglobin, 800 mg/l bilirubin and 8 g/l triglycerides. Method comparison study demonstrated an excellent correlation with both reference methods (r = 0.98 for ABX Pentra 400; 0.99 for AU 5800), though revealing a proportional bias of 19.7% (ABX Pentra 400) and 10.7% (AU 5800) respectively. TEobs was 26.7–31.9% and 16.7–21.9% and thus < TEmin. Healthy dogs presented with CRP values ≤11.9 mg/l.ConclusionsThe POCT precisely detects canine CRP at clinically relevant moderate and high CRP concentrations. The assay correlates well with both reference methods. Due to the bias, however, follow-up examinations should be performed with the same assay and analyzer.

Development of canine C-reactive protein assays

“…However, it also suggested that serum CRP levels higher than those seen in healthy control dogs obviously indicate higher levels of inflammation. While the evaluation of serum CRP levels must be considered in the context of the clinical disease condition, we suggest that CRP levels assayed by our ELISA can distinguish noninflammatory and inflammatory conditions using approximately 5 µg/mL as the cut-off value (mean + 3SD: 1.1 + 3 × 1.3 μg/mL) based on the results for the control group, and equivalent cut-off values (5.5 µg/mL) were seen with the Laser assay in this study and in previous reports [ 11 , 12 ].…”

“…3). Because the ICA produced negative results for samples with a level lower than 11.7 µg/mL and weak positive results for samples with a level higher than 6.0 µg/mL, the cut-off value of the ICA was suggested to be approximately 5-10 µg/mL, which is comparable to the cut-off values of commercial assays [11,12]. The cut-off value of the ICA was confirmed using diluted serum samples known CRP levels as approximately 5 µg/mL agreed with the results of clinical samples, producing negative results for samples with a level lower than 4.3 µg/mL and positive results for those with a level higher than 4.4 µg/mL ( Table 1).…”

“…Canine CRP ELISAs can be useful for routine checkups but are not appropriate as a rapid test for daily clinical use because of the time and labor required. Recently, commercially available canine CRP point-of-care (POC) assay kits, including quantitative immunoassays using analyzers [11,12] and semiqualitative immunochromatography assays (ICAs) [10], have been developed. Unfortunately, these kits may still require investigation as they tend to yield imprecise results [13].…”

Comparison of a point-of-care serum amyloid A analyzer frequently used in equine practice with 2 turbidimetric immunoassays used in human and veterinary medicine

“…Linearity under dilution was investigated by visual inspection of the correlation of observed SAA values plotted against a calculated (expected) SAA concentration. Percent recovery rate (RR) was calculated using the difference between actual and theoretical SAA concentration, as described for canine C-reactive protein (CRP) 14 :…”

Analytical performance and method comparison of a quantitative point-of-care immunoassay for measurement of bile acids in cats and dogs

“…The stock solutions were prepared as described previously. 19 The stock solution of the lipid emulsion was further diluted such that a final concentration of 4 g/L (dog) and 2 g/L (cat) was obtained, if necessary. Samples were analyzed in triplicate in random order.…”