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

Abstract

Magnesium sulfate (MgSO 4 ) was administered to calm competition horses. We evaluated the impact of regulatory requirements for the handling of blood samples on plasma ionized magnesium (iMg), ionized calcium (iCa), the iMg to iCa ratio, and pH.We hypothesized that iCa, iMg. and iMg/iCa would be similar among storage and collection methods. Four blood samples were collected from each of 50 horses on the same day: Group 1collection in a heparinized syringe and processed within hours in a clinical laboratory; Group 2collection into a plasma separator tube (PST) centrifuged just prior to analysis, and plasma processed as in (1); Group 3collection into a PST, refrigerated, shipped via overnight carrier to the United States Equestrian Federation (USEF) Equine Drug Testing and Research laboratory, centrifuged just prior to analysis, and plasma processed; and Group 4as in Group 3, but stored frozen at −80°C for 90 days, thawed, and plasma processed as in Group 3. Results for iMg/iCa are unit-less, adjusted iMg for potential influence of plasma protein and iCa, and highly correlated with iMg pH (r = −.933; P < 0.01). Samples processed immediately in a clinical reference laboratory had the greatest iMg/iCa. Both iMg/iCa and pH predictably decreased after freezing (P < 0.001). These data suggest that the iMg/iCa mirrors alterations in iMg regardless of storage and collection methods. This understanding can facilitate the development of a regulatory threshold for the control of the nefarious use of magnesium sulfate in competing horses, and an understanding of potential changes to iMg/iCa with storage of B samples. KEYWORDSionized calcium, ionized magnesium, ionized magnesium to ionized calcium ratio, magnesium sulfate, regulatory

Radio-Telemetric Assessment of Cardiac Variables and Locomotion With Experimentally Induced Hypermagnesemia in Horses Using Chronically Implanted Catheters

“…As total magnesium is not active, only Mg 2+ was monitored. The changes in Mg 2+ and Ca 2+ observed in this experiment were expected and consistent with previous research documenting experimentally induced hypermagnesemia (13, 14). As a result of the administration of MgSO 4 in this study, there were obvious and expected changes in the plasma concentration of Mg 2+ , Ca 2+ , and the ratio of Ca 2+ to Mg 2+ , some cardiovascular variables, as well as, changes in activity and observed behavior.…”

“…Our hypotheses were that the pharmacokinetics and decrease in blood pressure, compared to the 0.9% NaCl control, would be similar to our prior work; and utilizing sensitive accelerometers, a decrease in locomotion would be detected in the MgSO 4 treatment group compared to controls. We will also confirm that plasma subjected to the standard collection, storage, and shipping methods of the United States Equestrian Federation's Equine Drugs and Medications Program will have similar Mg 2+ and Ca 2+ as previously published (14).…”

“…Plasma samples were refrigerated, then shipped by commercial shipper within 48 h to the United States Equestrian Federation's Equine Drug Testing and Research Laboratory (EDTRL) in Lexington, Kentucky to duplicate the process used in the collection and analysis of regulatory samples (14). A Nova pHox Ultra Analyzer (Nova Biomedical, Waltham, MA) was used to analyze plasma samples for pH, TCO 2 , Mg 2+ , and Ca 2+ , and provided the Ca 2+ /Mg 2+ ratio.…”

Pharmacokinetics of magnesium and its effects on clinical variables following experimentally induced hypermagnesemia

“…This ratio mirrored the Mg 2+ concentrations and reflected a broader physiologic response. The Ca 2+ /Mg 2+ ratio and its inverse have been suggested as a biological marker for regulatory control of MgSO 4 (Schumacher, Yardley, & Bertone, 2018). The rapid decrease of the Ca 2+ /Mg 2+ ratio to less than one third of the baseline values within 5 min and not returning to near baseline values until 12 hr suggest a robust marker for MgSO 4 administration.…”

Effects of Intravenous Magnesium Sulfate on Calcium-Regulating Hormones, Plasma and Urinary Electrolytes in Healthy Horses

“…concentrations coupled with a high Mg 2+ /Ca 2+ ratio could be a potential biomarker for nefarious administration of MgSO 4 to competing horses [3,20].…”