Background

There are limited data on lactate stability in whole blood. The purpose of this study was to determine whole blood lactate stability at room temperature and in slushed ice conditions.

Methods

An equal number of arterial and venous samples were obtained from 202 subjects hospitalized for various pathophysiological conditions. Whole blood lactate concentration was measured over 5 different times spanning 80-90 min in a blood gas lab at a major hospital center. Samples were stored at room temperature (22-24°C) or in slushed ice conditions (0.1-0.2°C) before analysis.

Results

The mean increase in lactate concentration was 0.001 mmol/L/min in samples on slushed ice over 90 min. However, at room temperature conditions, the mean increase in lactate concentration was 0.008 mmol/L/min regardless of whether the sample was arterial or venous. An increase in whole blood lactate concentration of ≥ 0.4 mmol/L occured after 45 min at room temperature, with 5% of all whole blood specimens demonstrating a meaningful change at ≤ 20 min. The ≥ 0.4 mmol/L change in whole blood lactate is considered significant based on the College of American Pathologists instrument peer-group standards.

Conclusions

Considering that a change in whole blood lactate concentration of ≥ 0.4 mmol/L is unacceptable instrument peer-group variation as defined by the College of American Pathologists, ice is no longer needed to stabilize whole blood lactate specimens when the draw time to analyze time is < 45 min. Samples remain stable even at 90 min when left on ice.

Background

Data on the stability of whole blood electrolytes is limited to small sample sizes. We sought to determine the stability of whole blood electrolytes under room temperature and slushed iced conditions in human patients at a major hospital center.

Methods

Whole blood samples were obtained from 203 patients hospitalized for various pathophysiological conditions. Electrolyte concentrations of sodium, potassium [K+], ionized calcium, and chloride were measured at 5 different timepoints spanning 3 h. Samples were stored at room temperature (22-24 °C) or under slushed ice conditions (0.1-0.2 °C) before analysis.

Results

Under both conditions, sodium, ionized calcium, and chloride did not show a measurable change up to 109 min compared to baseline; however, the mean increase in [K+] over 138 min of storage in slushed ice was 0.0032 (0.0021 [5th percentile] to 0.0047 [95th percentile]) mmol/L/min (adjusted R2 = 0.62, P < 0.001). Five percent of the specimens demonstrated a ≥0.3 mmol/L change in [K+] from baseline after 67 min of storage in slushed ice. In contrast, 1% of the specimens stored at room temperature showed the same change at the same timepoint.

Conclusions

Whole blood sodium, [K+], ionized calcium, and chloride concentrations remain stable for at least 109 min at room temperature. However, whole blood specimens stored in slushed ice for not more than 67 min exhibit a 5% probability that the [K+] concentration will increase by at least 0.3 mmol/L compared to baseline. The other analytes do not destabilize for up to 178 min of slushed ice storage.