The Stability of Lactate Concentration in Preserved Blood Microsamples

Abstract

This study aimed to determine the stability of lactate concentration in blood samples preserved and stored using methods practical for field testing and experimental applications. Whole blood microsamples were obtained from venous samples drawn from 10 healthy subjects following bouts of moderate (approximately 5 mmol x l(-1), n = 12), or intense (approximately 10 mmol x l(-1), n = 12), treadmill exercise. Samples were analysed fresh (2 x 25 microl), or placed in preservative-containing tubes (12 x 75 microl) and analysed directly, or after storage at room temperature (RT) or 4 degrees C, for 1 h, 18 h, 2 d, 3 d or 7 d, or at -20 degrees C for 7 d. In comparison to preserved samples assayed directly after collection, lactate levels in all RT samples had declined significantly, whereas the 4 degrees C samples had not changed, by 2 d post-collection. After 7 d of refrigeration, the absolute value of the difference from lactate levels in samples measured after collection (mean +/- SD) was 0.38 +/- 0.34 mmol x l(-1), or 5.3 +/- 4.3%; with freezing, this difference was 0.27 +/- 0.27 mmol x l(-1), or 3.6 +/- 3.0%. These differences were less than the daily variation in the analyser readings of a 10 mmol x l(-1) standard, indicating that the blood preservation and storage methods identified herein are suitable for use during exercise testing.

Sodium lactate infusion during a cycling time‐trial does not increase lactate concentration or decrease performance

“…The current study used highly trained athletes, while our previous studies used healthy, but not trained, individuals. Indeed, previous studies have demonstrated an increased use of lactate as a fuel after exercise training (Bergman et al, 1999;Miller et al, 2002b), and that exogenous lactate infusion results in a decrease in glucose oxidation (Miller et al, 2002a). A second consideration is that exercise in the current study was performed at much higher flux rates than in our previous studies.…”

“…The sodium lactate infusion was mixed according to previously described procedures (Miller et al, 2002a(Miller et al, , 2002b. Briefly, a USP-certified 88% lactic acid solution (Sigma Chemical, Auckland, NZ) was mixed in USP-certified 2 n NaOH to a pH of 4.8.…”

“…Calibrated syringe pumps delivered the infusion solutions (Graseby 3400, Watford, UK). In contrast to our previous studies where infusion rates were varied to target a lactate concentration (Miller et al, 2002a(Miller et al, , 2002b, we used a constant infusion rate of 60 ml × h (1 for both trials, which during the sodium lactate trial equalled a lactate infusion rate of 116 mg× min (1 , which averaged 1.690.2 mg × kg (1 × min (1 per participant. The infusion rate was chosen based on the observation that an infusion rate of 1.74 mg × kg (1 × min (1 was enough to raise blood lactate concentration by approximately 2 mmol × l (1 in trained individuals cycling at 65% VO 2max (Miller et al, 2002a).…”

“…As evidenced by the number of portable lactate analysers available today, lactate concentration is one popular choice. In previous studies (Miller et al, 2002a(Miller et al, , 2002b, we infused sodium lactate into participants during low-and moderate-intensity exercise. We found that the rating of perceived exertion was not different when exercising at the same intensity with two different concentrations (approximately 2 and 4 mmol × l (1 ) of lactate.…”

“…Conversely, it was observed that workload, not plasma lactate concentration, was associated with perceived effort. The aforementioned studies (Miller et al, 2002a(Miller et al, , 2002b were limited to investigations of low-to moderate-intensity exercise, but they served to illustrate that effort could be dissociated from lactate concentration.…”