Accuracy of Hemolyzed Potassium Levels in the Emergency Department

In the emergency department (ED), pseudohyperkalemia from hemolysis may indirectly harm patients by exposing them to increased length of stay, cost, and repeat blood draws. The need to repeat hemolyzed potassium specimens in low-risk patients has not been well studied. Our objective was to determine the rate of true hyperkalemia among low-risk, adult ED patients with hemolyzed potassium specimens.

We conducted this prospective observational study at two large (129,000 annual visits) academic EDs in the mid-Atlantic. Data were collected from June 2017-November 2017 as baseline data for planned departmental quality improvement and again from June 2018-November 2018. Inclusion criteria were an initial basic metabolic panel in the ED with a hemolyzed potassium level > 5.1 milliequivalents per liter that was repeated within 12 hours, age (≥18, and bicarbonate (HCO₃) > 20. Exclusion criteria were age > 65, glomerular filtration rate (GFR) < 60, creatine phosphokinase > 500, hematologic malignancy, taking potassium-sparing or angiotensin-acting agents, or treatment with potassium-lowering agents (albuterol, insulin, HCO₃, sodium polystyrene sulfonate, or potassium-excreting diuretic) prior to the repeat lab draw.

Of 399 encounters with a hemolyzed, elevated potassium level in patients with GFR ≥ 60 and age > 18 that were repeated, we excluded 333 patients for age > 64, lab repeat > 12 hours, invalid identifiers, potassium-elevating or lowering medicines or hematologic malignancies.This left 66 encounters for review. There were no instances of hyperkalemia on the repeated, non-hemolyzed potassium levels, correlating to a true positive rate of 0% (95% confidence interval 0-6%). Median patient age was 46 (interquartile range [IQR] 34 - 56) years. Median hemolyzed potassium level was 5.8 (IQR 5.6 - 6.15) millimoles per liter (mmol/L), and median repeated potassium level was 3.9 (IQR 3.6 - 4.3) mmol/L. Median time between lab draws was 145 (IQR 87 - 262) minutes.

Of 66 patients who met our criteria, all had repeat non-hemolyzed potassiums within normal limits. The median of 145 minutes between lab draws suggests an opportunity to decrease the length of stay for these patients. Our results suggest that in adult patients < 65 with normal renal function, no hematologic malignancy, and not on a potassium-elevating medication, there is little to no risk of true hyperkalemia. Further studies should be done with a larger patient population and multicenter trials.