Effect of temperature, duration of storage and sampling procedure on ammonia concentration in equine blood plasma.

The effect of storage duration at different storage temperatures on the plasma ammonia concentration of equine EDTA whole blood, EDTA plasma and heparin plasma samples was investigated. Further, the effect of jugular vein compression before and during blood sampling on the plasma ammonia values was evaluated. In EDTA whole blood kept at 4 degrees C there was no significant increase of ammonia content after 6 hours of storage, whereas the increase was already significant 3 hours after collection if the EDTA whole blood was kept at 20-22 degrees C. EDTA plasma samples stored at 20-22 degrees C, 4 degrees C and -20 degrees C showed mean ammonia formation rates of 26.8 mumol/l, 6.6 mumol/l and 0.03 mumol/l per day, respectively. There were no differences between ammonia values of EDTA and heparin plasma samples immediately after sampling and following 3 days of storage at 4 degrees C and 3 and 90 days of storage at -20 degrees C. Although significant, the absolute differences between the mean plasma ammonia contents of EDTA blood sampled with and without compression of the jugular vein were small (20.2 +/- 4.1 mumol/l and 23.4 +/- 4.3 mumol/l resp.).