A comparison of total calcium, corrected calcium, and ionized calcium concentrations as indicators of calcium homeostasis among hypoalbuminemic dogs requiring intensive care

Authors


  • Research presented in part at the University of Missouri Phi Zeta Research Day March 2006 and the 12th International Veterinary Emergency and Critical Care Symposium, San Antonio, TX, 2006.

  • Dr. Kerl discloses that she has received support from Heska Corporation.
    The authors report no conflicts of interest.
    Grant Support: This study was supported by a grant from the Pi Chapter of Phi Zeta in the College of Veterinary Medicine at the University of Missouri.

Address correspondence and reprint requests to Dr. Claire R. Sharp, BSc, BVMS, Cummings School of Veterinary Medicine at Tufts University, 200 Westboro Rd, North Grafton, MA 01536. Email: claire.sharp@tufts.edu

Abstract

Objective – (1) To evaluate whether total calcium (tCa) correlates with ionized calcium (iCa) in hypoalbuminemic dogs; (2) to evaluate whether calcium adjusted for albumin (Alb), or total protein (TP), or both accurately predict iCa concentrations and hence can be used to monitor calcium homeostasis in critically ill hypoalbuminemic dogs; and (3) to evaluate factors associated with any potential discrepancy in calcium classification between corrected total and ionized values.

Design – Prospective observational clinical study.

Setting – Small animal intensive care unit in a veterinary medical teaching hospital.

Animals – Twenty-eight client-owned dogs with hypoalbuminemia.

Interventions – None.

Measurements and Main Results – iCa was determined using ion-specific electrode methodology, on heparinized plasma. The tCa concentration was adjusted for Alb and TP using published equations. In total 29% (8/28) of the hypoalbuminemic, critically ill dogs in this study were hypocalcemic at intensive care unit admission, as determined by iCa measurement. Corrected calcium values failed to accurately classify calcium status in 67.9% and 64.3% of cases, according to whether the Alb-adjusted or TP-adjusted values, respectively, were used. The sensitivity and specificity of the tCa to evaluate hypocalcemia was 100% and 47%, respectively. The sensitivity and specificity of the correction formulae were 37.5% and 79% for the Alb-adjusted values and 37.5% and 74% for TP-adjusted values. tCa overestimated the presence of hypocalcemia and underestimated the presence of normocalcemia, while corrected calcium values overestimated the presence of normocalcemia and underestimated the presence of hypocalcemia.

Conclusions – Calcium homeostasis in hypoalbuminemic critically ill dogs should be evaluated by iCa concentrations rather than tCa or calcium adjusted for Alb or TP. Given that tCa has 100% sensitivity for detecting hypocalcemia in this population it is recommended that all hypoalbuminemic and critically ill patients with low tCa should be evaluated with an iCa measurement.

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