Stability of beta-hydroxybutyrate in venous whole blood

Background Guidelines for diabetic ketoacidosis recommend serial beta-hydroxybutyrate measurement to judge treatment response. The manufacturer of the point-of-care ketone meter used in our laboratory requires venous whole blood to be analysed within 30 minutes of collection. This window is often missed in a centralised service, and specimens are rejected. We asked whether beta-hydroxybutyrate is stable beyond it. Methods Twenty consecutive lithium-heparin venous whole blood specimens were kept capped at room temperature and measured at 0.5, 1.0, 1.5, 2.0 and 2.5 hours after venepuncture on one Abbott FreeStyle Optium Neo H meter using a single strip lot. The 0.5 hour result was the baseline, this being the manufacturer's limit. The maximum permissible instability, set before analysis, was ±0.2 mmol/L or ±15% of baseline, whichever was greater. Paired differences were summarised as mean, SD, range and 95% confidence interval. Results Baseline concentrations ranged from 0.8 to 6.6 mmol/L (mean 3.6, SD 1.9). Mean differences from baseline were -0.07, -0.04, -0.04 and -0.02 mmol/L at 1.0, 1.5, 2.0 and 2.5 hours, with confidence intervals including zero from 1.5 hours. The largest absolute change was 0.5 mmol/L; the largest relative change, -22.2%, occurred in the specimen with the lowest baseline. All 80 paired observations met the criterion. The fitted instability slope was -0.9% per hour (95% CI -1.8 to 0.0). Conclusions Beta-hydroxybutyrate was stable for up to 150 minutes from venepuncture under these conditions, which supports extending the local acceptance window from 30 to 150 minutes.