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.