Ionized magnesium and calcium concentration and their ratio in equine plasma samples as determined by a regulatory laboratory compared to a clinical reference laboratory.

This study examines the effects of different blood sample storage and handling methods on the concentrations of ionized calcium (iCa) and ionized magnesium (iMg) in equine plasma. The research shows that these concentrations can fluctuate depending on these factors, providing important insights for establishing guidelines on the use of magnesium sulfate in competitive horse events.

Research Methodology

• The study analyzed the blood of 50 horses, with four samples collected from each.
• These samples were divided into four groups based on the collection and storage procedures.
• Group 1 samples were collected in a heparinized syringe and processed within hours in a clinical laboratory.
• Group 2 samples were collected into a plasma separator tube (PST) and centrifuged just prior to analysis, with the plasma processed similar to Group 1.
• Group 3 samples were also collected into a PST, but were refrigerated and shipped to the United States Equestrian Federation (USEF) Equine Drug Testing and Research laboratory for analysis.
• Group 4 followed the same process as Group 3, but the samples were stored frozen at -80°C for 90 days before being thawed and processed for analysis.

Research Findings

• The results showed a high correlation between iMg and pH levels (r = -.933; P < 0.01).
• Samples that were processed immediately in a clinical reference laboratory exhibited the highest iMg/iCa ratio.
• There was a predictable decrease in both iMg/iCa and pH levels after freezing (P < 0.001), suggesting that the iMg/iCa ratio can reflect alterations in iMg regardless of the storage and collection methods.

Conclusions and Implications

• This study offers valuable insights into how different sample collection and storage methods can impact ionized magnesium and calcium concentrations in equine plasma.
• This newfound understanding could help in the development of regulatory thresholds governing the use of magnesium sulfate in horse competitions.
• By understanding how these concentrations change with the storage of ‘B samples’ or backup samples, this research also offers useful information for future doping control and regulatory compliance in equestrian sports.