Effect of blood collection tubes on the incidence of artifactual hyperkalemia on patient samples from an outreach clinic

Background: An offsite satellite clinic of the University of Chicago Medical Center (UCMC) requested an investigation by the Clinical Chemistry Laboratory (CCL) into several cases of possible falsely elevated potassium (K⁺) values in their patients. Bloods for K⁺ and chemistry profiles are routinely collected in mint-green, heparinized plasma separator tubes (PST), centrifuged, and transported by courier from satellite clinic to CCL within several hours. Samples from on-site phlebotomy areas are similarly collected but sent uncentrifuged to CCL via a pneumatic tube system within minutes of collection. Methods: Our investigations included extensive QC and QA review of UCMC onsite and offsite outpatient clinics, reference range studies using PST and serum separator tubes (SST), assessment of pre-analytic handling of specimens, including transportation simulation study, and comparison of K⁺ results for samples collected simultaneously using PST and SST tubes at an offsite clinic. Results: Our transportation simulation demonstrated elevations in K⁺ concentrations following sample jostling and perturbations. We also observed RBC escape across the gel barrier further contributing to K⁺ elevations. Conclusion: Serum is preferred sample type for an offsite clinic.