Effect of Sample Handling and Storage Time on the Stability of Total Carbon Dioxide in Equine Plasma

A number of pre-analytical factors can influence the results of testing for the race-day administration of alkalinizing agents in horses. The results of this study demonstrate that failure to immediately centrifuge blood, or excessive delay in measuring the total CO₂ concentration (ctCO₂) in plasma after centrifugation, produces values for ctCO₂ in plasma that are lower than the true value.

1. Introduction

The stability of total CO₂ concentration (ctCO₂) in plasma is influenced by storage temperature and handling during sample processing. The objectives were to determine equine plasma ctCO₂ stability over 5 days when collected into partially evacuated blood collection tubes^a  , centrifuged within 30 minutes, and stored at 4°C, and to determine whether a delay in centrifugation increases the rate at which plasma ctCO₂ decreases over time.

2. Methods

Blood was collected from 6 adult horses into partially evacuated blood collection tubes^a  and randomly assigned to be centrifuged immediately or after storage for predetermined periods. Plasma ctCO₂ was measured in triplicate using a NOVA-4 analyzer at 0, 24, 48, 72, and 96 hours after collection. Data were analyzed using multivariable linear regression, and P < 0.05 was considered significant. 

3. Results

Plasma ctCO₂ decreased linearly over time during storage at 4°C. The measured value for ctCO₂ decreased at a faster rate (- 0.28 mmol//L per day; P < 0.0001) when centrifugation was delayed, compared with immediate centrifugation (- 0.10 mmol/L per day).

4. Discussion

Blood samples collected from horses into partially evacuated blood collection tubes^a should be centrifuged immediately after collection, stored at 4°C, and analyzed as soon as possible to ensure accurate values for plasma ctCO₂.

Footnote

^a Vacutainer, Becton Dickinson, Franklin Lakes, NJ 07417.