Validation of the Nova CRT8 for the measurement of ionized magnesium in feline serum.
BACKGROUND
Evaluation of serum magnesium (Mg) concentration is becoming important in human and veterinary critical care medicine. An ion-selective electrode can measure the physiologically active ionized fraction.


OBJECTIVE
The purpose of this study was to validate an ion-specific electrode analyzer and assay for measuring ionized Mg in feline serum and to determine a reference interval for this analyte in cats.


METHODS
Venous blood samples were collected anaerobically from clinically healthy cats, and the serum was used to validate the analyzer and assay. This included investigating the stability of samples stored at different temperatures, intra- and interassay precision, linearity, analytical sensitivity, and potential interferences from bilirubin, lipemia, hemoglobin, or serum separator tubes. A reference interval was calculated.


RESULTS
Serum samples evaluated for ionized Mg concentrations can be stored at 20 degrees C for < or =24 hours, at 4 degrees C for < or =72 hours, and at 20 degrees C for < or =4 weeks, when samples are minimally exposed to air. Intra- and interassay precisions had coefficients of variation (CVs) of 1.23% and 2.02%, respectively. There was good linearity using serum (r = .998; y = -0.0057 + 1.0256x) and manufacturer-supplied aqueous solutions and quality control materials (r = .999; y = 0.0110 + 0.9213x). Apparent analytical sensitivity was at least 0.015 mmol/L. Mean recovery was good for ionized Mg in samples with 1+ icterus (104%), 4+ lipemia (99.3%) and 1-4+ hemolysis (98.6%). There was no significant difference (P = .52) in ionized Mg concentrations in serum collected in tubes containing no additives compared with serum collected in glass separator tubes. The serum ionized Mg reference interval was 0.47-0.63 mmol/L (n = 40).


CONCLUSIONS
The Nova CRT8 analyzer and assay provide a precise and reliable method of measuring ionized Mg concentration in feline serum. Strict adherence to sampling techniques, handling, and storage are necessary for reliable results.
Gilroy
Cornelia V
CV
Department of Pathology and Microbiology, Atlantic Veterinary College, Charlottetown, Prince Edward Island, Canada. cgilroy@upei.ca
Burton
Shelley A
SA
Horney
Barbara S
BS
Mackenzie
Allan L
AL
D000818:Animals; D001774:Blood Chemical Analysis / Q000295:instrumentation* / Q000662:veterinary; D002415:Cats / Q000097:blood*; D008274:Magnesium / Q000097:blood*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling
D008274:Magnesium