Comparative performance of IDEXX SDMA Test and the DLD SDMA ELISA for the measurement of SDMA in canine and feline serum

Abstract

Kidney disease is common in companion animals, and traditionally diagnosed with serum creatinine concentration (sCr), blood urea nitrogen, and abnormal urinalysis findings. Symmetric dimethylarginine (SDMA) is a novel kidney biomarker that reflects glomerular filtration rate, increasing earlier than sCr with acute kidney injury and chronic kidney disease. This prospective study compared accuracy and precision of two commercial SDMA assays, the IDEXX SDMA Test and the DLD SDMA ELISA, relative to the established reference method, liquid chromatography/mass spectrometry (LC-MS). Thirty canine and 30 feline pooled serum samples were used to evaluate accuracy compared to LC-MS. Pooled canine samples with a low SDMA concentration and pooled feline samples with a high SDMA concentration were used to evaluate precision. Using a best fit linear model, the IDEXX SDMA Test resulted in a slope of 1.06 and an intercept of 0.34, with R2 = 0.99, and the DLD SDMA ELISA resulted in a slope of 0.37 and an intercept of 11.33, with R2 = 0.27, when compared to LC-MS. Estimated bias over a clinically relevant range for SDMA (10–45 μg/dL) was 1–2 μg/dL for the IDEXX SDMA Test, while DLD SDMA ELISA showed considerable bias, 5–8 μg/dL. Day-to-day precision analysis of the low SDMA concentration samples showed 7.7% total coefficient of variation (CV) for the IDEXX SDMA Test and 31.1% for the DLD SDMA ELISA. For the high SDMA concentration samples, total CV was 2.3% for the IDEXX SDMA Test and 28.2% for the DLD SDMA ELISA. In this study the IDEXX SDMA Test was more accurate and more precise in macroscopically normal serum than the DLD SDMA ELISA when compared to the reference method of LC-MS. The IDEXX SDMA Test is more suitable for clinical use in the diagnosis and monitoring of kidney disease in dogs and cats.

Serum symmetric dimethylarginine shows a relatively consistent long-term concentration in healthy dogs with a significant effect of increased body fat percentage

“…The minimal difference in CV I between both studies is probably attributable to a small increase in biological variation over time as both studies applied the same assay and minimalized analytical variance by batch analyses of the samples at the end of the study. However, a substantial proportion of the within-subject variability is probably caused by the analytical error of the applied assay as a considerably high analytical variability ranging from 7.7% to 10% has been reported for the IDEXX SDMA test [ 19 , 52 , 53 ].…”

“…Complete elimination of the analytical variance was not possible, though, due to the difference in storage length between the first and last collected samples. The second limitation is the relatively high analytical variability of the applied SDMA assay, which has been reported to be between 7.7% and 10% [ 19 , 52 , 53 ]. According to published guidelines, the CV A of an analytical method should be <0.5 CV I to have a desirable performance [ 69 ].…”

First autochthonous case of clinical Hepatozoon felis infection in a domestic cat in Central Europe

“…Hematologic and biochemical analysis of blood samples revealed leukopenia (3.7 G/l; reference range 3.9-19 G/l) characterized by lymphopenia (lymphocytes 595/μl; reference range 850-5850/μl) and mild neutropenia (segmented neutrophils 2604/μl; reference range 2620-15,170/μl); mild thrombocytopenia (149 G/l; reference range 155-641 G/l); anisocytosis, and slightly increased serum levels of symmetric dimethylarginine (SDMA) (18 μg/dl; reference range 0-14 μg/dl) and bilirubin (0.5 mg/dl; reference range 0-0.4 mg/dl). SDMA was determined using a commercially available high-throughput immunoassay (IDEXX SDMA® Test; IDEXX Laboratories Inc.) [26]. Serum levels of calcium were slightly reduced (2.1 mmol/l; reference range 2.2-2.9 mmol/l) and magnesium was elevated (1.3 mmol/l, reference range 0.6-1.1 mmol/l).…”

First report of Cytauxzoon sp. infection in Germany: organism description and molecular confirmation in a domestic cat

“…In March 2017, a complete blood count and serum clinical biochemical analysis (including the assessment of liver, kidney and pancreatic parameters) were performed at IDEXX reference laboratory in Ludwigsburg, Germany (Table 1 ). Symmetric dimethylarginine (SDMA) was measured using a commercially available high-throughput immunoassay (IDEXX SDMA Test, IDEXX Laboratories Inc.; Ernst et al 2018 ). No urine examination was performed.…”