Objectives: Symmetric dimethylarginine (SDMA) reflects the glomerular filtration rate (GFR) in people, dogs and cats. Initial assays used a liquid chromatography-mass spectroscopy (LC-MS) technique. A veterinary immunoassay has been developed for use in commercial laboratories and point-of-care (POC) laboratory equipment. This study sought to: determine POC and commercial laboratory (CL) SDMA assay imprecision; determine any bias of the POC assay compared with the CL assay; calculate observed total error of the POC assay and compare with analytical performance goals; and calculate dispersion and sigma metrics (σ) for POC and CL SDMA methods. Methods: Two separate studies were performed that assessed: (1) imprecision, determined by evaluation of pooled feline plasma or serum; and (2) bias, assessed by comparing pooled plasma and serum results, as well as paired analyses of clinical samples from a single venepuncture measured using both analysers. Results were assessed in relation to performance goals. Dispersion and σ were calculated for both analysers. Results: Bias between CL and POC analysers was consistent and high numbers of clinical results were outside performance goals across both studies. Imprecision was poor for both analysers for study 1 and improved to within quality goals for the CL analyser for study 2. Dispersion was at least 40%, meaning a measured result of 14 μg/dl represents a range of possible results from 8 μg/dl to 20 μg/dl. Conclusions and relevance: Clinicians should be careful ascribing medical significance to small changes in SDMA concentration, as these may reflect analytical and biological variability. Analyser-specific reference intervals are likely required.

We report the results of validation of canine serum cortisol determination with the Immulite 2000 Xpi cortisol immunoassay (Siemens), with characterization of precision (CV), accuracy (spiking-recovery [SR] bias), and observed total error (TEo = bias + 2CV) across the reportable range, specifically at the most common interpretation thresholds for dynamic testing. Imprecision increased at increasing rate with decreasing serum cortisol concentration and bias was low, resulting in increasing TEo with decreasing serum cortisol concentration. Inter-laboratory comparison study allowed for determination of range-based bias (RB) and average bias (AB). At 38.6 and 552 nmol/L (1.4 and 20 μg/dL), between-run CV was 10% and 7.5%, respectively, and TEo ~30% and ~20%, respectively (TEo remained similar regardless of the considered bias: SR, RB, or AB). These analytical performance parameters should be considered in the interpretation of results and for future expert consensus discussions to determine recommendations for allowable total error (TEa). Importantly, the commonly used thresholds for interpretation of results were determined ~40 y ago with different methods of measurements and computation, hence updating is desirable. Quality control material (QCM) had between-run imprecision of 4% for QCM1 and 7% for QCM2; the bias was minimal for both levels. Acceptable QC rules are heavily dependent on the desired TEa for the QCM system (TEa_QCM), itself limited by the desired clinical TEa. At low TEa_QCM (20–33%), almost no rules were acceptable, whereas at high TEa_QCM (50%), almost all rules were acceptable; further investigation is needed to determine which TEa_QCM can be guaranteed by simple QC rules.

Background: Laboratory and instrument harmonization is seldom reported in the veterinary literature despite its advantages to clinical interpretation, including the use of interchangeable results and common reference intervals within a system of laboratories.Objectives: A three‐step process was employed to evaluate and optimize performance and then assess the appropriateness of common reference intervals across a network of six Sysmex XT‐2000iV hematology analyzers at 5 commercial veterinary laboratory sites. The aims were to discover if harmonization was feasible in veterinary hematology and which quality parameters would best identify performance deviations to ensure a harmonized status could be maintained.Methods: The performance of 10 measurands of a commercially available quality control material (Level 2—Normal e‐CHECK (XE)‐Hematology Control) was evaluated during three 1‐month time periods. Precision and bias were assessed with Six Sigma, American Society of Veterinary Clinical Pathology (ASVCP) total error quality goals and biologic variation (BV)‐based quality goal approaches to performance measurement.Results: Instrument adjustments were made to 1 analyzer twice and 3 analyzers once between evaluations to improve performance and achieve harmonization. Sigma metrics improved from 37/50 > 6 to 58/60 > 6 and to all >5 over the course of the harmonization project. BV‐based quality goals for desirable bias and for laboratory systems of 0.33 × CV_I (within‐subject biologic variation) were more sensitive and useful for assessing performance than the ASVCP total error goals.Conclusions: Optimization and harmonization were achieved, and because BV‐derived bias goals were achieved, common reference intervals could be implemented across the network of analyzers.

We report here validation of the Immulite 2000 Xpi cortisol immunoassay (Siemens; with kit lot numbers <550) for measurement of urine cortisol in dogs, with characterization of the precision (CV), accuracy (spiking-recovery [SR] bias), and observed total error (TEo = bias + 2CV) across the reportable range. Linearity assessed by simple linear regression was excellent. Imprecision, SR bias, and TEo increased markedly with decreasing urine cortisol concentration. Interlaboratory comparison studies determined range-based (RB) bias and average bias (AB). The 3 biases (SR, RB, and AB) and resulting TEo differed markedly. At 38.6 and 552 nmol/L (1.4 and 20 μg/dL), between-run CVs were 10% and 4.5%, respectively, and TEo_RB were ~30% and 20%, respectively, similar to observations in serum in another validation study. These analytical performance parameters should be considered for urine cortisol:creatinine ratio (UCCR) result interpretation, given that, for any hypothetical errorless urine creatinine measurement, the error % on UCCR mirrors the error % on urine cortisol. Importantly, there is no commonly used interpretation threshold for UCCR, given that UCCR varies greatly depending on measurement methods and threshold computation. To date, there is no manufacturer-provided quality control material (QCM) with target values for urine cortisol with an Immulite; for Liquicheck QCM (Bio-Rad), between-run imprecision was ~5% for both QCM levels. Acceptable QC rules are heavily dependent on the desired total allowable error (TEa) for the QCM system, itself limited by the desired clinical TEa.