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

Pseudonormokalemia case report - What does it mean to have normal blood potassium?

This case report describes a case of pseudonormokalemia, true hypokalemia. Often, only laboratory values outside the normal range gain attention and false normal results are at risk of not being noticed. However, a disease state may be masked by another pathological process. Here, a 50-year old male was admitted to the Department of Internal Medicine due to sepsis from a dental infection. Initially, serum potassium measurement revealed a normal value of 4 mmol/L (reference interval 3.8-5.1 mmol/L). Thrombocyte number was above 500x109/L. Due to our policy to recommend a repeated measurement of potassium in whole blood or heparin plasma if a patient has thrombocytosis, pseudonormokalemia was identified because the heparin plasma potassium value was only 2.9 mmol/L (reference interval 3.5-4.8 mmol/L). The physiological difference between serum and plasma concentration is no more than 0.3 mmol/L. In this case, potassium concentration were falsely elevated in the serum sample, probably caused by the high number of platelets releasing potassium during clotting. Interpretative comments in patients with thrombocytosis over 500x109/L recommending plasma potassium measurement are helpful. The best way to eliminate pseudohyperkalemia and pseudonormokalemia phenomena caused by thrombocytosis is to completely change towards heparin plasma as the standard material.

The influence of undetected hemolysis on POCT potassium results in the emergency department

OBJECTIVES

This study aimed to evaluate discrepancies in potassium measurements between point-of-care testing (POCT) and central laboratory (CL) methods, focusing on the impact of hemolysis on these measurements and its impact in the clinical practice in the emergency department (ED).

METHODS

A retrospective analysis was conducted using data from three European university hospitals: Technische Universitat Munchen (Germany), Hospital Universitario La Paz (Spain), and Erasmus University Medical Center (The Netherlands). The study compared POCT potassium measurements in EDs with CL measurements. Data normalization was performed in categories for potassium levels (kalemia) and hemolysis. The severity of discrepancies between POCT and CL potassium measurements was assessed using the reference change value (RCV).

RESULTS

The study identified significant discrepancies in potassium between POCT and CL methods. In comparing POCT normo- and mild hypokalemia against CL results, differences of -4.20 % and +4.88 % were noted respectively. The largest variance in the CL was a +4.14 % difference in the mild hyperkalemia category. Additionally, the RCV was calculated to quantify the severity of discrepancies between paired potassium measurements from POCT and CL methods. The overall hemolysis characteristics, as defined by the hemolysis gradient, showed considerable variation between the testing sites, significantly affecting the reliability of potassium measurements in POCT.

CONCLUSIONS

The study highlighted the challenges in achieving consistent potassium measurement results between POCT and CL methods, particularly in the presence of hemolysis. It emphasised the need for integrated hemolysis detection systems in future blood gas analysis devices to minimise discrepancies and ensure accurate POCT results.

Impact of potassium test sample rejections on routine laboratory service, South Africa

Background

Accurate potassium measurements are necessary for effective clinical management of hyperkalaemia. Pre-analytical factors may affect laboratory measurements, leading to erroneous results and inappropriate patient management and negatively impact the efficiency and finances of laboratories and hospitals.

Objective

This study evaluated the impact of rejected potassium test requests on laboratory service.

Methods

We conducted a retrospective descriptive study to assess potassium test data at a public laboratory in Pretoria, Gauteng, South Africa, using samples collected from an academic hospital, peripheral hospitals, and outpatient clinics between January 2018 to December 2018. We assessed the relationship between reasons for rejection and health facility type, as well as financial implications for the laboratory.

Results

The potassium result rejection rate was 15.1% (29 806 samples), out of the 197 405 requests received. The most common reasons for rejection were old sample (> 1 day old) (41.4%; 12 348 rejections) and haemolysis (38.2%; 11 398 rejections). The most frequent reason for rejections at the central, academic hospital was haemolysis (42.0%), while old sample was the most common reason for rejection at peripheral hospitals (43.4%; 4119/9493 requests) and outpatient health facilities (57.2%; 7208/12 605 requests) (p = 0.022). The total cost of potassium sample rejection over the study period was substantial, given the resource constraints in this setting.

Conclusion

Peripheral hospitals and outpatient departments accounted for the majority of rejected potassium testing results, possibly resulting from delays in transportation; causing substantial financial impact on the laboratory. Improved sample collection, handling, and expedited transportation are recommended.

What this study adds

This study highlights the importance of appropriate sample collection and handling and the undesirable consequences of non-adherence to these pre-analytical considerations.