Abstract

Background: Pseudohyperkalaemia may result from delay in centrifugation and storage at 4°C. We investigated whether the stage of chronic kidney disease (CKD), its aetiology or medications influence this.

Methods: Seventy-seven patients with CKD were recruited. Lithium heparin plasma samples were analysed for sodium, potassium, urea and creatinine, chloride, bicarbonate, magnesium, calcium and inorganic phosphate at 0 h and after storage of whole blood at 4°C for 6 h and 20 h. K-EDTA and fluoride-EDTA samples were analysed for full blood count and glucose at 0 h. CKD stage was determined by standard criteria.

Results: K⁺ increased on average by 1.0 and 3.6 mmol/L after 6 and 20 h storage of whole blood at 4°C, independent of cause or stage of CKD. K⁺ increase at 6 h was correlated with haemoglobin but not with white blood cell count, platelet count or glucose. Patients taking ACE inhibitors and/or angiotensin receptor blockers (ARBs) had slightly higher K⁺ at 0 h and increased K⁺ after storage for 6 h. Na⁺ decreased on average by 3.8 mmol/L at 20 h and was independent of CKD stage, and correlated with K⁺ increase.

Conclusions: K⁺ increased significantly with time in samples stored at 4°C in all stages of CKD. This was greater in some patients on ACE inhibitors and ARBs, and increased with haemoglobin, but was not related to the stage of CKD, white blood cell count or platelet count for the samples used in this study.