Plasma homocysteine concentrations in healthy horses and horses with atrial fibrillation

Introduction

Homocysteine (HCY) is an amino acid produced from methionine metabolism. Plasma homocysteine concentrations ([HCY]_p) are elevated (>13 μmol/L) in people with atrial fibrillation (AF) and can predict the recurrence of AF after cardioversion. This study aimed to validate a commercially available human HCY assay for use in horses to develop reference intervals for [HCY]_p and compare [HCY]_p in healthy horses and horses with AF.

Animals

Healthy horses (n = 27) and horses with AF (n = 55, 34 of which were cardioverted using transvenous electrical cardioversion).

Materials and methods

Blood samples were analysed for HCY using an automated enzyme-cycling assay (Homocysteine Cobas C, Integra, Roche) and creatinine (compensated Jaffe method). Assay linearity and precision were assessed, reference intervals calculated and [HCY]_p and creatinine compared between groups.

Results

The assay was precise (coefficient of variation 1.6–4.3%, n = 10 repetitions) and provided linear results (r = 0.99 for spiked and natural samples) for a range of [HCY]_p. The reference interval for [HCY]_p was 1.5–7.8 μmol/L. The plasma concentration of homocysteine was 4.65 ± 1.5 μmol/L (mean ± standard deviation) in healthy horses and 4.65 ± 1.72 μmol/L in horses with AF (p=0.99); [HCY]_p was not associated with recurrence of AF (n = 18, p=0.97). A weak, positive correlation between plasma creatinine and [HCY]_p was detected (r = 0.295, p=0.008, r² = 0.11).

Conclusions

This assay allows precise measurement of [HCY]_p in horses. Unlike in people, [HCY]_p is not increased in horses with AF and cannot predict AF recurrence. This might be due to differences in the underlying pathological mechanisms of AF development in people and horses.