Investigation of outpatients referred to a chemical pathologist with potential pseudohyperkalaemia

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.

Spurious Electrolyte and Acid-Base Disorders in the Patient With Cancer: A Review

Electrolyte and acid-base disorders are frequently encountered in patients with malignancy, either due to cancer itself or as a complication of its therapy. However, spurious electrolyte disorders can complicate the interpretation and management of these patients. Several electrolytes can be artifactually increased or decreased such that the serum electrolyte values do not correspond to their actual systemic levels, potentially resulting in extensive diagnostic investigations and therapeutic interventions. Examples of spurious derangements include pseudohyponatremia, pseudohypokalemia, pseudohyperkalemia, pseudohypophosphatemia, pseudohyperphosphatemia, and artifactual acid-base abnormalities. Correctly interpreting these artifactual laboratory abnormalities is imperative for avoiding unnecessary and potentially harmful interventions in cancer patients. The factors influencing these spurious results also must be recognized, along with the steps to minimize them. We present a narrative review of commonly reported pseudo electrolyte disorders and describe strategies to exclude erroneous interpretations of these laboratory values and avoid pitfalls. Awareness and recognition of spurious electrolyte and acid-base disorders can prevent unnecessary and harmful treatments.

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.

The impact of centrifugation in primary care on pseudohyperkalaemia: a retrospective evaluation

Background

Spurious hyperkalaemia is a relatively common occurrence in samples originating from primary care. Failure to identify spurious hyperkalaemia carries a significant risk of patient mismanagement. We have carried out a retrospective evaluation to review the impact of the use of centrifuges in primary care for biochemistry blood samples on the management of hyperkalaemia.

Methods

Serum potassium concentrations in samples received from primary care were reviewed for six months prior to and after the implementation of on-site centrifugation. Samples exhibiting significant hyperkalaemia (serum potassium >6.0 mmol/L) were further investigated to ascertain the degree of patient follow-up.

Results

There was a significant decrease in the number of samples exhibiting marked hyperkalaemia following the implementation (2244 versus 524; P < 0.0001). In terms of patient follow-up, we observed a reduction in the number of patients exhibiting pseudohyperkalaemia that previously had led to inappropriate hospital admissions over the same time period (6 cases postimplementation versus 22 cases preimplementation). We also observed an increase in the number of patients exhibiting true hyperkalaemia during the six-month period postimplementation (33 cases postimplementation versus 6 cases preimplementation).

Conclusions

The centrifugation of serum samples in primary care improves the sample quality and the integrity of the potassium results reported. We have also demonstrated evidence of an improvement in patient management and quality of care.

The severity of pseudohyperkalaemia is not dependent upon the stage of chronic kidney disease: a prospective study

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.