Erroneous potassium results: preanalytical causes, detection, and corrective actions

Potassium is one of the most requested laboratory tests. Its level is carefully monitored and maintained in a narrow physiological range. Even slightly altered potassium values may severely impact the patient's health, which is why an accurate and reliable result is of such importance. Even if high-quality analytics are available, there are still numerous ways in which potassium measurements may be biased, all of which occur in the preanalytical phase of the total laboratory testing process. As these results do not reflect the patient's in-vivo status, such results are referred to as pseudo-hyper/hypokalemia or indeed pseudo-normokalemia, depending on the true potassium result. Our goal in this review is to present an in-depth analysis of preanalytical errors that may result in inaccurate potassium results. After reviewing existing evidence on this topic, we classified preanalytical errors impacting potassium results into 4 categories: 1) patient factors like high platelet, leukocytes, or erythrocyte counts; 2) the sample type 3) the blood collection procedure, including inappropriate equipment, patient preparation, sample contamination and others and 4) the tube processing. The latter two include sample transport and storage conditions of whole blood, plasma, or serum as well as sample separation and subsequent preanalytical processes. In particular, we discuss the contribution of hemolysis, as one of the most frequent preanalytical errors, to pseudo-hyperkalemia. We provide a practical flow chart and a tabular overview of all the discussed preanalytical errors including possible underlying mechanisms, indicators for detection, suggestions for corrective actions, and references to the according evidence. We thereby hope that this manuscript will serve as a resource in the prevention and investigation of potentially biased potassium results.

Atypical hereditary spherocytosis phenotype associated with pseudohypokalaemia and a new variant in the band 3 protein

Red blood cell (RBC) membrane disorders are predominantly caused by mutations resulting in decreased RBC deformability and permeability. We present a family in which, the proband and his daughter presented with pseudohypokalaemia. Studies on the temperature dependence of pseudohypokalaemia suggested a maximum decrease in serum potassium when whole blood is stored at 37°C. Routine haematology suggested mild haemolysis with a hereditary spherocytosis phenotype. These two cases present a novel variant in temperature-dependent changes in potassium transport. A new variant was identified in the SLC4A1 gene which codes for band 3 protein (anion exchanger 1) in RBC membrane which may contribute to the phenotype. This is the first report of familial pseudohypokalaemia associated with changes in RBC membrane morphology. The clinical implications of pseudohypokalaemia are that it can lead to inappropriate investigation or treatment. However, many questions remain to be solved and other RBC membrane protein genes should be studied.

Pseudohyperkalaemia in leukaemic patients: the effect of test tube type and form of transport to the laboratory

Background

The present study was aimed at determining the effect of the tube type used for primary sample collection and the manner of transport prior to assessment (either manual or by pneumatic tube) on the degree of pseudohyperkalaemia in leukaemic patients.

Methods

Blood from six leukaemic patients was collected into seven primary sample tubes (Monovette®, Sarstedt): sample A, heparinized blood gas syringe (potassium reference value); sample B, plasma Li-heparin without separator gel; sample C, plasma Li-heparin with separator gel; and sample D, serum with separator gel. The primary sample tubes designated B, C and D were transported to the laboratory manually. Duplicates of the same sample tubes, BPT, CPT and DPT, were sent to the laboratory by pneumatic tube.

Results

In patients with chronic lymphocytic leukaemia (CLL), there was no increase in the concentration of potassium in samples B, C and D when compared to the reference value. Transport of the samples by pneumatic tube led to a pronounced increase in potassium concentration in samples BPT and CPT, whereas there was no increase in sample DPT when compared to the reference value. In the patient with chronic myeloid leukaemia (CML), an increase in potassium concentration occurred in sample D and in samples BPT, CPT and DPT. A similar finding was observed in the patient with acute lymphocytic leukaemia (ALL), furthermore with an extremely high concentration of potassium in samples C and CPT.

Conclusions

Manual transport of non-coagulable blood (plasma Li-heparin without separator gel) to the laboratory results in the least possible artificial increase in potassium concentration in the sample.