A Prospective Study Regarding the Need for Repeat Potassium Testing in ED Patients with Hemolysis-Associated Pseudo-Hyperkalemia

Objectives: Many ED patients who have hyperkalemia (HK) with evidence of hemolysis have pseudohyperkalemia (PHK) and may not require repeat potassium (K) testing, though ED physicians often redraw levels. We sought to determine if a set of patients with PHK could be determined who would not require repeat K draws based on lab and medication/co-morbid conditions.

Methods: This was a prospective IRB-approved study at an 85,000 patient/yr inner-city ED. Data was analyzed to determine whether repeat K draws were necessary in patients with HK plus hemolysis who had normal renal function (NFR) defined by either Cr or GFR and to determine factors that might lower retest threshold and prevent unnecessary repeat K testing. Normal renal function was defined as Cr < 1.3 or GFR > 60 (calculated by the Modification of Diet in Renal Disease (MDRD) equation:. HK was defined as K > 5.3 mEq/L. ED patients with K draws showing HK plus hemolysis with repeat metabolic panel performed within 12 hours were eligible.

Results: 300 patients had HK with hemolysis with repeat testing during the study period. Four were excluded due to missing/incomplete data. Two patients had renal failure and were excluded. 238 had repeat K sent prior to, or without specific HK treatment and were further analyzed. The median age was 60, range 76, IQR 46-75. 153/238 (64.2%) were female, 200/238 African-American (84%), 169/238 (71%) had normal GFR while 182/238 (76.8%) had normal Cr. Twenty-four of the 238 (10%) had persistent HK on the 2^nd lab draw. Factors on univariate analysis associated with HK on repeat testing were age, gender, diuretic use, PVD, DM, and abnormal BUN, Cr or GFR. Binary logistic regression showed abnormal Cr, age and PVD as significant predictors of persistent HK. ROC curves of Cr and age were generated and further analysis showed Cr >1.4, age > 63, or PVD would have identified 22/24 cases of persistent hyperkalemia (the two patients showing persistent hyperkalemia had potassium levels that did not require treatment). This resulted in a decreased need for retesting in 53.7% of patients.

Conclusion: By using 3 variables: Cr >1.4, age > 63, and history of PVD, 115/214 (53.7%) of patients with initial HK with hemolysis would not require repeat blood draw for potassium testing, while 2/24 patients with persistent HK would have been missed. These 2 patients had marginally elevated potassium that would not have required treatment. Since some variables reported to be associated with hyperkalemia were not present or were present in low numbers, physicians may need to repeat testing on select or sicker patients who they suspect may have true HK, however up to 50% of patients will not require such testing.