Pneumatic tube system transport and false hyperkalemia related to leukocytosis: a retrospective analysis.

Extreme leukocytosis may lead to false hyperkalemia when blood samples are conveyed by pneumatic tube system (PTS). The aim of this study was to define whether even moderate leukocytosis and also non malignancy cells like neutrophils may influence potassium values after PTS transportation.

Uncentrifuged blood samples are sent to the local laboratory through PTS. Data were retrospectively collected from routine testing carried out on all specimens arrived in the laboratory between September 2017 and March 2018. Clinical chemistry testing is routinely performed using lithium-heparin tubes. When false hyperkalemia induced by leukocytosis is suspected, potassium measurement is then performed in serum (clotting activator tubes) or whole blood samples. The analysis was focused on samples with both leukocytosis (i.e., >15×10⁹/L) and plasma potassium >5.0 mmol/L, before any corrective therapeutic measure to lower potassium levels was established.

A total number of 18 samples were included in our analysis, 9 drawn from patients with hematologic malignancies and 9 without. In the 9 patients without hematologic malignancies (median leukocyte count, 20.4×10⁹/L), the median potassium value was 5.4 mmol/L in plasma and 4.5 mmol/L in serum or whole blood. In the 9 patients with hematologic malignancies (median leukocyte count, 151.9×10⁹/L; p <0.001), the median potassium value was 7.7 mmol/L in plasma and 4.3 mmol/L in serum or whole blood (median difference, 2.9 mmol/L; p <0.001).

The results of our study suggest that even modest leukocytosis (i.e., around 15x10⁹/L), which can be frequently encountered in clinical practice, may be associated with a significant variation of plasma potassium. This would lead us to conclude that plasma samples transportation by PTS should be avoided in patients with even mild leukocytosis.