Reliability of the i‐STAT for the determination of blood electrolyte (K+, Na+, and CI−) concentrations in cattle

Background

Rapid determination of blood electrolyte concentrations can help determine electrolyte status and delivery of effective volume of electrolyte solutions in field conditions.

Objective

To evaluate reliability of the i‐STAT, a point‐of‐care (POC) device, in measuring blood K⁺, Na⁺, and CI ⁻ concentrations in cattle.

Animals

Ninety‐eight cattle with various diseases.

Methods

In this prospective study, blood samples collected from the jugular vein were processed for determination of K⁺, Na⁺, and CI ⁻ concentrations in blood and plasma using the i‐STAT and auto‐analyzer (Cobas C501), respectively. Blood and plasma electrolyte data were subjected to student t‐test for comparison, the concordance analysis for agreement, accuracy, and precision, the Passing‐Bablok regression and the Bland‐Altman plot for reliability, and receiver operating characteristics curves for sensitivity (Se) and specificity (Sp).

Results

Plasma concentrations of K⁺ (4.39 versus 4.2 mmol/L; P < .0001) and CI ⁻ (100.30 versus 99.4 mmol/L; P < .04) were greater than their concentrations in blood. Plasma and blood Na⁺ concentrations were similar (136.95 versus 136.8 mmol/L). The i‐STAT results were highly correlated with the Cobas C501 results (r = 0.970, 0.922, and 0.866 for K⁺, Na⁺, and CI ⁻, respectively). Regression equations fitting blood (Y) and plasma (X) concentration did not deviate from the identity line for K⁺ (Y = −0.10 + 0.98 × X), Na⁺ (Y = X), and CI ⁻ (Y = 3.04 + 0.96 × X). The mean bias (blood concentration ‐ plasma concentration) was −0.20 for K⁺ (P = .03), −0.16 for Na⁺ (P = .12), and −0.87 for CI ⁻ (P = .93). The i‐STAT had 76–100% Se and 87.7–100% Sp for assessing electrolyte statuses.

Conclusions and Clinical Importance

The i‐STAT yielded results that were in agreement with the auto‐analyzer, with negligible biases in measurement of plasma K⁺, Na⁺, and CI ⁻ concentrations. The i‐STAT is a reliable POC device and can be used in field condition to assess electrolyte status in cattle.     

Evaluation of the Accutrend for lactate measurement in dogs

BACKGROUND: Lactate concentrations are increasingly quantified in dogs using point-of-care instruments, but often without canine-specific method evaluation and instrument-specific reference intervals. OBJECTIVES: The objectives of this study were to 1) determine the precision of the Accutrend (Roche Diagnostics) for lactate determination in dogs, 2) determine the accuracy of the Accutrend using the Rapidlab 865 (Bayer Diagnostics) as the reference method, and 3) establish and compare reference intervals for lactate concentration in clinically healthy dogs for both instruments. METHODS: Precision was evaluated using low and high control materials, and variable (1 drop) and fixed (25 microL) sample volumes. Accuracy was determined by comparing lactate concentrations obtained with the Accutrend with those from the Rapidlab 865 in 273 heparinized canine jugular venous blood samples from 100 clinically healthy dogs and 107 systemically ill dogs (173 samples). Lactate reference intervals were established for both analyzers using data from the 100 clinically healthy dogs. RESULTS: The precision of the Accutrend was good (coefficients of variation, < or = 5.3%) for 25-microL samples but not when a drop was used. Lactate concentrations obtained on the Accutrend correlated poorly with those from the Rapidlab 865 (r = 0.864, mean bias = 0.66 mmol/L, 95% confidence interval [CI] = 0.57-0.76 with 95% limits of agreement = -0.87 (lower limit, 95% CI = -1.03 to -0.71) and 2.20 (upper limit, 95% CI = 2.04 to 2.36). The reference interval for canine lactate concentration on the Accutrend was 1.2-3.1 mmol/L compared with 0.46-2.31 mmol/L on the Rapidlab. CONCLUSION: Although precision was good with fixed sample volumes, blood lactate concentrations obtained on the Accutrend were significantly different than those on the Rapidlab 865, with systematic and random errors resulting in a positive bias. Further evaluation of the Accutrend is required before its use in dogs can be recommended.     

Evaluation of a point‐of‐care blood glucose monitor in healthy goats

Objective

To assess agreement between a point‐of‐care glucometer (POCG) and a laboratory chemistry analyzer for blood glucose measurements in goats.

Design

Prospective study.

Setting

University teaching hospital.

Animals

Eighteen healthy adult goats.

Investigations

Whole blood samples were obtained via jugular venipuncture prior to premedication with xylazine and butorphanol (T0), following premedication (T20), and after 1 hour of inhalant anesthesia (T60). Each sample was tested with a POCG and a laboratory analyzer (HITA). Agreement was assessed using concordance correlation coefficients and calculation of bias and 95% limits of agreement.

Measurements and Main Results

Mean blood glucose concentration at T0 was 3.9 ± 0.6 mmol/L (70 ± 10 mg/dL; POCG) and 2.9 ± 0.4 mmol/dL (53 ± 8 mg/dL; HITA). Glucose concentrations at T20 were 6.7 ± 2.4 mmol/L (121 ± 43 mg/dL) and 5.4 ± 2.1 mmol/L (97 ± 37 mg/dL) and at T60 were 5.7 ± 1.7 mmol/L (102 ± 31 mg/dL) and 4.7 ± 1.3 mmol/L (85 ± 24 mg/dL) when measured with the POCG and HITA, respectively. The POCG overestimated blood glucose compared to the HITA. The bias ± SD was 1.08 ± 0.53 mmol/L (19.4 ± 9.5 mg/dL) (95% LOA 0.04 to 2.11 mmol/L [0.7 to 38.0 mg/dL]) and the concordance correlation coefficient was 0.82. After correcting the results of the POCG using a mixed‐effects linear model, the bias was 0.0 ± 0.38 mmol/L (0.0 ± 6.8 mg/dL) (95% LOA ± 0.74 mmol/L [± 13.4 mg/dL]) and the concordance correlation coefficient was 0.98.

Conclusions

The POCG overestimated blood glucose concentrations in goats, compared to the HITA, but when the POCG concentrations were corrected, the agreement was excellent.