Use of a water hardness test kit to measure serum calcium concentration incattle

Objective-To determine whether a commercially available water hardness test kit could be used to measure total serum calcium concentration and diagnos e hypocalcemia in dairy cows. Design-Prospective study. Animals-30 dairy cows from 19 commercial herds. Procedure-Serum calcium concentration was determined using a water hardness test kit and a standard. laboratory-based method. Simple linear regression was used to determine whether there was a linear relationship between resu lts of the 2 methods, and Spearman's rank correlation was used to calculate correlation between measurements. Sensitivity, specificity, and predictive values of using test kit-derived values for diagnosis of hypocalcemia (lab oratory value < 8 mg/dl) were calculated. Results-There was a high correlation and significant linear relationship be tween results of the 2 methods. Sensitivity, specificity, predictive value of a positive test result, and predictive value of a negative lest result w ere 100, 73, 86, and 100%, respectively. Accuracy was improved by using a t est kit-derived calcium concentration of 7 mg/dl as the cut-off for determi ning hypocalcemia. Clinical implications-Results indicate that a commercially available water hardness test kit can be used as a rapid, inexpensive method of estimating serum calcium concentrations and diagnosing hypocalcemia in dairy cattle. H owever, the lest is not practical for cow-side use, because blood samples m ust be centrifuged to obtain serum for use in the test kit.