The gold standard for assessing hypocalcemia is through measurement of blood ionized calcium (iCa) concentration. We assessed the use of a Horiba LAQUAtwin ionized Ca meter in comparison to the Abaxis Vetscan iSTAT as cow-side tools to measure iCa. Three groups of nonlactating, non-pregnant Holstein cows were fed negative DCAD rations with low, medium or high concentrations of total dietary Ca and then subjected to a controlled induction of hypocalcemia. Low Ca cows (n = 5) were fed 0.45% Ca, medium Ca cows (n = 6) were fed 1.13% Ca, and high Ca cows (n = 6) were fed 2.02% Ca. Average DCAD was −15.1 mEq/100g DM for all cows resulting in urine pH values below 6.0. All cows were fed for 21 d before hypocalcemia was induced using intravenous infusion of 5% ethylene glycol tetraacetic acid (EGTA), a selective iCa chelator. Blood samples were collected every 15 min throughout infusion and analyzed for iCa by the Horiba LAQUAtwin and Abaxis Vetscan iSTAT until 60% of preinfusion iCa was achieved. Blood samples were taken post-infusion at 0, 2.5, 5, 10, 15, 30, and every 30 min thereafter and analyzed for iCa by both meters until 90% of preinfusion iCa was achieved. The LAQUAtwin was calibrated before every measurement, as this is critical to ensure proper function. We utilized a likelihood ratio to determine whether variance of the 2 m were equal when measuring iCa concentrations during EGTA challenge and recovery period. Variance for the iSTAT was 0.02745, while variance for the Horiba meter was 0.14447. The chi-squared value was significant (P < 0.0001). These results indicate that the Horiba meter is more variable when measuring blood iCa concentration and produces values that are significantly higher than values obtained from the iSTAT (P < 0.001). The Horiba LAQUAtwin meter is less likely to accurately identify a cow with clinical or subclinical hypocalcemia than the Abaxis Vetscan iSTAT.