Preliminary evaluation of a gel tube agglutination major cross-match method in dogs.

BACKGROUND: A major cross-match gel tube test is available for use in dogs yet has not been clinically evaluated. OBJECTIVES: This study compared cross-match results obtained using the gel tube and the standard tube methods for canine samples. METHODS: Study 1 included 107 canine sample donor-recipient pairings cross-match tested with the RapidVet-H method gel tube test and compared results with the standard tube method. Additionally, 120 pairings using pooled sera containing anti-canine erythrocyte antibody at various concentrations were tested with leftover blood from a hospital population to assess sensitivity and specificity of the gel tube method in comparison with the standard method. RESULTS: The gel tube method had a good relative specificity of 96.1% in detecting lack of agglutination (compatibility) compared to the standard tube method. Agreement between the 2 methods was moderate. Nine of 107 pairings showed agglutination/incompatibility on either test, too few to allow reliable calculation of relative sensitivity. Fifty percent of the gel tube method results were difficult to interpret due to sample spreading in the reaction and/or negative control tubes. CONCLUSIONS: The RapidVet-H method agreed with the standard cross-match method on compatible samples, but detected incompatibility in some sample pairs that were compatible with the standard method. Evaluation using larger numbers of incompatible pairings is needed to assess diagnostic utility. The gel tube method results were difficult to categorize due to sample spreading. Weak agglutination reactions or other factors such as centrifuge model may be responsible.

Evaluation of ionized and total serum magnesium concentrations in hyperthyroid cats.

Hyperthyroidism can increase the renal excretion of magnesium and thus cause hypomagnesemia in various species. Anaerobically collected blood samples from 15 hyperthyroid and 40 normal, healthy cats were analyzed with an ion-selective electrode analyzer and a serum biochemical analyzer. There was no significant difference in ionized or total serum magnesium concentration between the 2 groups, but there was a significant difference (P = 0.004) in the ratio of ionized to total serum magnesium concentrations between the healthy cats and the hyperthyroid cats with thyroxine (T4) concentrations at or above the median. There was a significant correlation (r = 0.894, P = 0.000) between the ionized and total magnesium concentrations in the hyperthyroid cats. The hyperthyroid cats had a significantly lower (P = 0.003) total serum protein concentration than the healthy cats. A significant negative correlation (r = -0.670, P = 0.006) was detected between the ionized magnesium and logarithmically transformed total T4 concentrations in the hyperthyroid cats, which suggests that the severity of hyperthyroidism may contribute to a decrease in the ionized magnesium concentration.

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. OBJECTIVES: 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.

Evaluation of an automated, homogeneous enzyme immunoassay for serum thyroxine measurement in dog and cat serum.

A homogenous enzyme immunoassay (EIA) for measurement of serum thyroxine (T4) concentration was evaluated for use with canine and feline serum. The EIA method was linear from 0 to 150 nmol T4/L for human serum, 0 to 94 nmol T4/L for feline serum and 10 to 60 nmol T4/L for canine serum. Intra- and interassay precision studies yielded coefficients of variation