A comparative study of reducing the extracellular potassium concentration in red blood cells by washing and by reduction of additive solution

Extracellular potassium concentration (K(+)) increases in the supernatant of whole and packed red blood cell units (pRBCs) with duration of refrigerated storage in citrate-phosphate-dextrose-adenine (CPDA-1) and additive solution (AS). Studies have shown that to avoid hyperkalemia, washed pRBCs are preferred if relatively fresh pRBCs are not available. To determine whether a simpler procedure, AS reduction, results in lowering of K(+) in pRBCs comparable to that achieved by washing, the K(+) levels by both methods were compared.

Pre- and post-K(+) levels were measured in 6 washed and 11 AS-reduced pRBC units. Each unit was weighed, hematocrit was determined, K(+) was measured, and total K(+) was calculated. Washed units were 3 to 21 and AS-reduced units were 4 to 30 days old. Statistical analysis was performed with a t test.

There was no significant difference (p > 0.35) in the initial K(+) between the two groups (mean +/- SD, 36.95 +/- 13.16 mEq/L before washing and 39.78 +/- 19.94 mEq/L before AS reduction). Washing and AS reduction both led to a significant decrease in K(+) levels (2.15 +/- 0.10 mEq/L after washing and 4.41 +/- 3.04 mEq/L after AS reduction, each p < 0.0005). Washing, however, was significantly better than AS reduction in reducing K(+) in stored pRBCs (p < 0.05).

Washing pRBCs results in very low levels of K(+). AS reduction also significantly reduces K(+) levels. Selection of the method of K(+) reduction will depend on the stringency of K(+) reduction needed, the time constraints, and the availability of facilities and staff for washing.