Heparinised blood ionised calcium concentrations in horses with colic or diarrhoea compared to normal subjects.
Authors: van der Kolk J H, Nachreiner R F, Refsal K R, Brouillet D, Wensing Th
Journal: Equine veterinary journal
Summary
# Editorial Summary Ionised calcium (ICa) plays a crucial role in neuromuscular function and coagulation, yet reference ranges and measurement stability in horses remain poorly characterised. Van der Kolk and colleagues established baseline ICa concentrations in healthy Warmbloods (51 ± 2.7% of total calcium; 1.43–1.75 mmol/l), intact PTH values (0.6 ± 0.3 pmol/l), and validated the stability of heparinised blood samples over 102 hours at room temperature and through six freeze–thaw cycles. The authors developed and tested a pH-adjusted regression formula for predicting ICa at standardised pH 7.4, which performed accurately in normal horses but slightly underestimated values in colic and diarrhoea cases (by 0.2–0.3% respectively). For clinicians managing horses with acid–base disturbances, this work provides practical tools to interpret ICa measurements whilst acknowledging that disease-specific physiological changes may require formula adjustment—particularly valuable given that acid–base shifts alter the proportion of ionised to protein-bound calcium independent of total serum calcium concentration.
Read the full abstract on PubMed
Practical Takeaways
- •Reference ranges for ionised calcium in heparinised blood for normal horses are established (1.43–1.75 mmol/l), useful for clinical laboratories assessing calcium status in colic and diarrhoea cases
- •Heparinised blood samples are stable for ionised calcium analysis over extended storage periods, allowing flexibility in sample handling and transport to reference laboratories
- •A validated pH-adjustment formula is now available to standardize ionised calcium results to pH 7.4, improving comparability of results across different disease states and clinical settings
Key Findings
- •Mean ionised calcium in heparinised blood of normal Warmbloods was 51 ± 2.7% of total calcium, with range 1.43–1.75 mmol/l across two institutions
- •Intact PTH concentration in normal horses measured 0.6 ± 0.3 pmol/l in EDTA plasma
- •A linear regression equation was derived to predict adjusted ionised calcium at pH 7.4, with excellent accuracy in healthy horses (100% match to actual analyser values) and minor underestimation in disease states (0.2–0.3%)
- •Heparinised blood and serum ionised calcium concentrations showed stability after 102 hours storage at room temperature and six freeze-thaw cycles