Spurious elevation of serum potassium concentration measured in samples with thrombocytosis

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.

Pseudohyperkalemia caused by essential thrombocythemia in a patient with chronic renal failure: A case report

BACKGROUND

Hyperkalemia is one of the most common complications of chronic renal failure. Pseudohyperkalemia is caused by elevated levels of serum potassium in vitro and is usually accompanied by thrombocythemia. Although an elevated level of potassium is typically correlated with impaired renal function, pseudo-hyperkalemia has been rarely reported in patients with chronic renal failure. Here, we conducted a review of the literature to study the case of pseudo-hyperkalemia caused by the essential thrombocythemia in a patient with chronic renal failure.

CASE SUMMARY

A 73-year-old woman was admitted to our hospital with complaints of palpitation, dyspnea, and acratia for 2 d and a history of essential throm-bocythemia for 1 year. The routine blood test showed platelet count of 1460 × 10⁹/L, and biochemistry tests showed that the patient suffered from hyperkalemia (potassium: 7.50 mmol/L) and renal failure (estimated glomerular filtration rate: 8.88 mL/min). Initial treatment included medicines to lower her potassium-levels and hemodialysis. However, the therapy did not affect her serum potassium levels. Plasma potassium concentration measurements and a history of essential thrombocythemia established the diagnosis of pseudohyperkalemia. The treatments of the platelet disorder gradually normalized serum potassium levels; however, the treatments had to be discontinued later due to the severe leukopenia, and enhanced levels of serum potassium concentrations were observable in the patient. Since plasma sampling was not permitted, doctors had to use a diuretic just in case. Finally, the patient collapsed into unconsciousness and died due to multiple organ dysfunction and electrolyte disturbance.

CONCLUSION

We reviewed the literature and suggest that serum and plasma potassium values should both be measured for patients whose platelet counts exceed 500 × 10⁹/L to eliminate chances of pseudohyperkalemia, especially for those with chronic renal failure. An inappropriate treatment for pseudohyperkalemia can aggravate a patient's condition.

A statistical model for restoration of serum potassium level disturbed by hemolysis

BACKGROUND

Blood sample hemolysis affects pre-analytical quality and may cause pseudohyperkalemia. We established a statistical model to estimate the corrected potassium (K⁺) in serum.

METHODS

Serum K⁺ and H index were analyzed, and blood cell index was obtained from the examined Full Blood Examination (FBE) results. A linear-regression model was developed using hemolysis (H) index, K⁺ and covariates of blood cell index from 139 cell lysates of blood samples. The model was then validated against 26 in vitro physically hemolyzed serum samples.

RESULTS

The final model selected H index, hemoglobin concentration (HGB), and hematocrit (HCT) as important predictors in estimating the K⁺ content. The model was validated against artificially hemolyzed serum samples, which returned a correlation of 0.942 between observed and predicted net K⁺ increase by hemolysis. The predictors H index, HCT, and HB contributed 93.7%, 3.5% and 2.8% to the model R², respectively.

CONCLUSION

In vitro hemolysis induced pseudohyperkalemia could be accurately predicted and restored by our model for clinical application.