Long term stability of lactate in uncentrifuged sodium fluoride/potassium oxalate blood collection tubes.

Background: Delayed time from collection to centrifugation may cause erroneously high lactate levels in vitro (from continued blood cell metabolism under anaerobic conditions in the collection tube) if not collected in appropriate collection devices, consequently increasing the risk for inappropriate patient care or harm. We undertook a study to determine the turnaround time for lactate testing in a tertiary care setting and also performed short- and long-term lactate stability studies in blood collected in sodium fluoride/potassium oxalate (NaF/KOx) collection tubes.

Methods: The hospital lab information system was mined for 6 months to determine patient samples that may have exceeded the time from collection-to-receival in lab of 15-min. Lactate stability was evaluated in unspun NaF/KOx collection tubes at 15 min intervals for to 2 h; and separately at 2, 6, 12, 24, and 48-h post-collection.

Results: A total of 8,929 plasma samples were collected in 6 months, and 1/3 were not received in the lab within 15 min from collection. In NaF/KOx additive, lactate levels had minor increases over 2 h, and incremental increases at an average rate of 0.0035 mmol/L/h over 48 h with maximum increase of 9.8% at 48 h. However, the average change across all time points were within local allowable performance goals (at ≤4 mmol/L ± 0.5 mmol/L; at >4 mmol/L ± 12%).

Conclusion: A small proportion of lactate specimens may experience delay in processing. Although lactate levels may incrementally increase over 48-h at room temperature in unspun NaF/KOx collection tubes, the changes may not be clinically impactful.