Biological variation of biochemical analytes determined at 8-week intervals for 1 year in clinically healthy cats.

BACKGROUND: Biological variation helps determine whether population-based or subject-based reference intervals are more appropriate to assess changes in serial analytical values. Previous studies have investigated the biological variation of biochemical analytes weekly or with variable frequency over 5-14 weeks in cats, but none have considered biological variation at less frequent intervals over 1 year. OBJECTIVES: We aimed to evaluate the long-term biological variation of 19 biochemical analytes in clinically healthy cats. METHODS: A prospective, observational study in which 15 clinically healthy, client-owned cats were sampled for serum biochemical analyses every 8 weeks for 1 year. Frozen serum samples were single-batch analyzed. Restricted maximum likelihood estimation was used to determine the coefficients of variation (CV), describing variation within each cat, between cats, and the analytical variation. These CVs were used to determine the indices of individuality and reference change values (RCVs). RESULTS: Albumin, alkaline phosphatase, creatine kinase, and globulin had high indices of individuality, indicating that they are best evaluated by RCVs. Phosphorus, potassium, chloride, sodium, symmetric dimethylarginine, and total CO2 had low indices of individuality, indicating that population-based reference intervals are appropriate. Alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, calcium, cholesterol, creatinine, glucose, total bilirubin, and total protein had intermediate indices of individuality, indicating that RCVs may provide additional insight into the interpretation of analyte measurements beyond the population-based reference intervals. CONCLUSIONS: For many analytes, the biological variation detected was similar to that reported in prior studies. Clinicians should consider the biological variation of analytes to best interpret clinically relevant changes in serial analyte measurements.

Accuracy of the IDEXX SediVue Dx analyzer for quantifying RBC and WBC indices in the urine sediments of cats and dogs compared with manual microscopic evaluations.

BACKGROUND: The IDEXX SediVue Dx (SediVue) is an automated, in-clinic urine sediment analyzer for veterinary patients. The bias between the results from manual microscopy and the SediVue is currently unknown. OBJECTIVES: To assess the diagnostic accuracy of the SediVue, we aimed to determine the bias between the SediVue (index test) and manual microscopy (reference standard) for the quantification of RBCs and WBCs in urine. METHODS: Urine remnant samples were collected from cats and dogs that contained RBCs (n = 462) and WBCs (n = 510). Retrospective analysis of results from urine sediment examinations using both manual microscopy (using a KOVA and DeciSlide system) and the SediVue (1.0.1.3) was performed. Bias was determined with Bland-Altman plots. SediVue-captured images from high-bias samples were reviewed, and biases were compared. RESULTS: The median bias for semi-quantitative RBC and WBC counts was determined for RBC and WBC counts. The cutoffs were RBC ≤ 5/HPF, 0.3; RBC 5.1-10/HPF, 10.1; RBC 10.1-20/HPF, 10.6; and RBC > 20/HPF, 28.93; WBC ≤ 5/HPF, 0.1; WBC 5.1-10/HPF, 2.2; WBC 10.1-20/HPF, 9.4; and WBC > 20/HPF, 26.6. High bias between the methods was identified in 98 samples (21.0%) with RBCs and 77 samples (15.7%) with WBCs. Reviewer-based enumeration of the SediVue-captured images decreased the percentage of samples with high bias to 17.3% for RBCs and to 11.4% for WBCs. CONCLUSIONS: Bias in the RBC and WBC counts between manual microscopy and the SediVue was unlikely to impact clinical interpretations in a majority of cases. Although reviewer enumeration of SediVue-captured images reduced observed bias, inherent differences between methodologies appeared to have a larger impact on the bias.

Biologic variation of symmetric dimethylarginine and creatinine in clinically healthy cats.

BACKGROUND: Biologic variation of biochemical analytes, both within individuals and between individuals, determines whether population-based reference intervals (RIs) are appropriate when interpreting if a particular change is clinically relevant for a specific individual. OBJECTIVES: We aimed to evaluate the biologic variation of symmetric dimethylarginine (SDMA) in clinically healthy cats. METHODS: A prospective, observational study was performed in which 10 clinically healthy, client-owned cats were sampled for serum biochemical analyses once weekly for 6 weeks. Serum samples were frozen, and then single batches were analyzed for SDMA, using both liquid chromatography-mass spectroscopy (LC-MS), and an enzyme multiplied immunoassay technique (EMIT), and creatinine by modified Jaffe method. Restricted maximum likelihood estimations were used to determine the coefficients of variation (CVs) describing variation within each cat, between cats, and the analytical variation. These CVs were used to determine the indices of individuality and reference change values (RCVs). RESULTS: SDMA had an intermediate index of individuality that could be evaluated by both RCV and population-based RIs. In contrast, creatinine had a high index of individuality best evaluated with RCVs. Serum SDMA concentrations evaluated with either the reference standard, LC-MS, or the clinically used EMIT yielded similar results. CONCLUSIONS: Clinicians should consider biologic variation when selecting the best method for interpreting changes in biochemical analytes. Specifically, establishing each cat's baseline serum creatinine and SDMA concentrations during health, and applying RCVs to subsequent measurements could improve the recognition of meaningful biologic changes.

Hyperthyroidism is not a risk factor for subclinical bacteriuria in cats: A prospective cohort study.

BACKGROUND: Subclinical bacteriuria is defined as a positive bacterial urine culture in the absence of clinical evidence of urinary tract infection (UTI). Studies have reported that hyperthyroid cats have UTIs (mostly subclinical) with prevalence rates of 12%-22%. Consequently, clinicians consider hyperthyroidism a risk factor for development of subclinical bacteriuria, and many recommend urine culture when evaluating hyperthyroid cats. OBJECTIVES: To compare the prevalence of subclinical bacteriuria (based on positive urine culture) in untreated hyperthyroid cats to that in euthyroid cats of similar age and sex. ANIMALS: Three hundred and ninety-three hyperthyroid cats presented for radioiodine treatment and 131 euthyroid cats (≥7 years of age) presented for routine examination. Cats with signs of lower urinary tract disease were excluded. METHODS: Prospective cohort study. Both hyperthyroid and euthyroid cats had urine collected by cystocentesis for complete urinalysis and culture. Data pertaining to age, sex, body condition, and serum thyroxine and creatinine concentrations also were acquired. Logistic regression was performed to evaluate for potential risk factors for subclinical bacteriuria. RESULTS: Hyperthyroid cats showed a low prevalence of subclinical bacteriuria (4.3%), which did not differ from that found in euthyroid cats (4.6%). Of the signalment factors evaluated, only female sex was a significant risk factor (odds ratio [OR], 6.9; P = .002). Furthermore, positive urine cultures were more likely in specimens with dilute urine concentration (<1.035), pyuria, or microscopic bacteriuria. CONCLUSIONS AND CLINICAL IMPORTANCE: Hyperthyroid cats are not at risk for subclinical bacteriuria. In the absence of lower urinary tract signs, no clinical benefit exists in routinely performing urine cultures when evaluating hyperthyroid cats.

Comparison of 2 assays for measuring serum total thyroxine concentration in dogs and cats.

BACKGROUND: No gold standard assay for serum total thyroxine (TT4) concentration in small animals exists. The Microgenics DRI TT4 (MTT4) assay is used by most reference laboratories. HYPOTHESIS/OBJECTIVES: IDEXX Catalyst Total T4 (CTT4) and Immulite 2000 TT4 (ITT4) results will agree with MTT4 results. ANIMALS: Residual small animal sera were randomized before reanalysis (dogs, CTT4 versus MTT4: n = 176, ITT4 versus MTT4: n = 74; cats, CTT4 versus MTT4: n = 319, ITT4 versus MTT4: n = 79). METHODS: Validation and method comparison study. Serum TT4 concentration was measured on all analyzers. Pairwise Pearson correlation, cumulative sum linearity test, regression, and Bland-Altman method were performed. RESULTS: CTT4 versus MTT4 in dogs: constant bias (y-intercept) was 0.10 µg/dL (95% confidence interval [CI], 0.05-0.15), proportional bias (slope) was 0.86 µg/dL (95% CI, 0.83-0.89); in cats, constant bias was 0.13 µg/dL (95% CI, 0.08-0.20) and proportional bias was 1.01 µg/dL (95% CI, 0.98-1.03), but the test for linearity failed. Bland-Altman plots identified increasing disagreement with increasing serum TT4 concentrations. ITT4 versus MTT4 in dogs, constant bias was 0.14 µg/dL (95% CI, 0.04-0.22) and 0.22 µg/dL (95% CI, 0.09-0.33) for cats; proportional bias was 0.76 (95% CI, 0.72-0.80) for dogs and 0.71 (95% CI, 0.69-0.74) for cats. CONCLUSIONS AND CLINICAL IMPORTANCE: Differences in CTT4 and MTT4 results affect interpretation at higher serum TT4 concentrations. The ITT4 proportional bias will underestimate serum TT4 concentrations in dogs and cats, compared to MTT4. Serial TT4 measurements should be done using the same assay.

Comparison of the performance of the IDEXX SediVue Dx® with manual microscopy for the detection of cells and 2 crystal types in canine and feline urine.

BACKGROUND: Microscopic evaluation of urine is inconsistently performed in veterinary clinics. The IDEXX SediVue Dx® Urine Sediment Analyzer (SediVue) recently was introduced for automated analysis of canine and feline urine and may facilitate performance of urinalyses in practice. OBJECTIVE: Compare the performance of the SediVue with manual microscopy for detecting clinically relevant numbers of cells and 2 crystal types. SAMPLES: Five-hundred thirty urine samples (82% canine, 18% feline). METHODS: For SediVue analysis (software versions [SW] 1.0.0.0 and 1.0.1.3), uncentrifuged urine was pipetted into a cartridge. Images were captured and processed using a convolutional neural network algorithm. For manual microscopy, urine was centrifuged to obtain sediment. To determine sensitivity and specificity of the SediVue compared with manual microscopy, thresholds were set at ≥5/high power field (hpf) for red blood cells (RBC) and white blood cells (WBC) and ≥1/hpf for squamous epithelial cells (sqEPI), non-squamous epithelial cells (nsEPI), struvite crystals (STR), and calcium oxalate dihydrate crystals (CaOx Di). RESULTS: The sensitivity of the SediVue (SW1.0.1.3) was 85%-90% for the detection of RBC, WBC, and STR; 75% for CaOx Di; 71% for nsEPI; and 33% for sqEPI. Specificity was 99% for sqEPI and CaOx Di; 87%-90% for RBC, WBC, and nsEPI; and 84% for STR. Compared to SW1.0.0.0, SW1.0.1.3 had increased sensitivity but decreased specificity. Performance was similar for canine versus feline and fresh versus stored urine samples. CONCLUSIONS AND CLINICAL IMPORTANCE: The SediVue exhibits good agreement with manual microscopy for the detection of most formed elements evaluated, but improvement is needed for epithelial cells.

Urine sediment examination: Potential impact of red and white blood cell counts using different sediment methods.

BACKGROUND: Centrifugation is the primary method used to perform urine sediment analyses, but evaluation of other methods is required to validate centrifugation. OBJECTIVES: Non-urine materials were used to examine the repeatability (precision) and effectiveness (recovery) of four sediment methodologies on red blood cell (RBC) and white blood cell (WBC) counts. METHODS: Four urine sediment methods were compared using commercially available quality control material (QCM) and fresh canine RBCs in a diluent. Treatments included (a) 5 mL centrifugation at 390g for 5 minutes; (b) 1.5 mL centrifugation at 3900g for 45 seconds; (c) 60 µL of neat (unspun urine) in a microtiter well; and (d) 30 µL of neat on a slide with a coverslip. A within-run precision using QCM was followed by a one-run comparison test performed with a suspension of canine erythrocytes. RBC morphology was also examined. RESULTS: All results are listed in order of Methods A-D. Percent coefficients of variation (%CVs) for WBCs were 23.2%, 33.7%, 15.0%, and 27.2%. Red blood cells %CVs were 34.3%, 29.2%, 16.2%, and 24.4%. Average WBC counts in ten fields of view (FOV) ± 1 SD were 26.4 ± 6.1, 14.2 ± 4.8, 32.8 ± 4.9, and 1.6 ± 0.4. Average RBC counts in 10 fields of view (FOV) ± 1 SD were 45.3 ± 15.5, 23.9 ± 7.0, 38.4 ± 6.2, and 2.6 ± 0.6. The one-run comparison test reports average RBC counts per FOV at 55.2, 23.4, 92.8, and 13.8. The percentages of abnormal RBCs were 92.2%, 74.8%, 7.0%, and 55.1%. CONCLUSIONS: Method C had the best reproducibility, a lower frequency of cell morphology abnormalities, and similar cellular counts to those of Methods A and B.

Determining resolution of Angiostrongylus vasorum in dogs following anthelmintic treatment with an imidacloprid 10 per cent/moxidectin 2.5 per cent spot-on.

OBJECTIVES: To determine the time from treatment with a product containing imidacloprid 10 per cent/moxidectin 2.5 per cent spot-on (Advocate™), to dogs becoming negative for Angiostrongylus vasorum (A. vasorum). The authors hypothesised that most dogs would have resolution of A. vasorum within four weeks of treatment with Advocate™. DESIGN: Prospective, non-randomised, prepost treatment study. SETTING: Cases were enrolled from general practices along the southern coast of the United Kingdom. PARTICIPANTS: Nine dogs completed the study and were enrolled if A. vasorum had been diagnosed based on a positive commercially available, in-clinic, serological A. vasorum antigen test (Angio Detect®) or Baermann performed at an external laboratory or both. INTERVENTIONS: The only treatment A. vasorum-positive dogs received was Advocate™ which was applied at the time of diagnosis and reapplied if necessary at four-weekly intervals until dogs tested negative by Angio Detect. PRIMARY OUTCOME MEASURES: Angio Detect® was performed and Advocate™ was reapplied at four-weekly intervals until dogs tested negative by this method. SECONDARY OUTCOME MEASURES: Baermann was also performed at four-weekly intervals until dogs tested negative by this method. RESULTS: Application of Advocate™ was an effective treatment for A. vasorum infection in dogs and resulted in resolution of the infection, based on Angio Detect® testing and Baermann, within four weeks, in eight out of nine dogs. Post-treatment Angio Detect® testing was concordant with Baermann in seven of nine dogs. CONCLUSIONS: Application of Advocate™ was an effective treatment for A. vasorum infection in dogs and resulted in resolution of the infection within four weeks in most dogs. Repeat Angio Detect® testing is recommended following treatment of A. vasorum to confirm resolution of the infection.

Comparison of in-clinic point-of-care and reference laboratory total thyroxine immunoassays for diagnosis and post-treatment monitoring of hyperthyroid cats.

Objectives The Catalyst One Chemistry Analyzer (IDEXX Laboratories) is a point-of-care instrument that can measure total thyroxine (TT4) by immunoassay. The aims of this study were to evaluate the analytic performance of the Catalyst TT4 assay in feline sera and to examine agreement of the Catalyst TT4 results with those measured by immunoassay at a veterinary reference laboratory. Methods Assay precision, reproducibility and linearity were evaluated for the Catalyst TT4 assay. For method comparison, TT4 concentrations in serum samples from 157 cats (127 hyperthyroid, 30 radioiodine-treated cats) were analyzed by both in-clinic and reference laboratory methods. Results The Catalyst TT4 demonstrated good precision and reproducibility (coefficients of variation ⩽8.5%) and excellent linearity in the diagnostic range of 6-150 nmol/l. Differences between the two TT4 methods showed no proportional or fixed bias (Bland-Altman plots) but did demonstrate greater spread of values at higher TT4 concentrations. Statistical analysis of percent differences between methods indicated 95% limits of agreement of ± 30%. When serum TT4 concentrations were classified as low, high or within the reference interval (12-50 nmol/l) for each assay, there was strong agreement (96.8%) in classification between methods. Conclusions and relevance The Catalyst TT4 assay provided precise serum TT4 concentrations in the 157 samples analyzed, which agreed well with results provided by a reference laboratory. Cats with Catalyst TT4 concentrations near decision thresholds (eg, normal vs high) should either have TT4 concentration repeated a few weeks later and/or undergo further testing (eg, free T4, serum thyroid-stimulating hormone, thyroid scintigraphy) to determine thyroid status.