EFFECT OF PLATELET COUNT ON SERUM AND PLASMA POTASSIUM - EVALUATION USING DATABASE INFORMATION FROM 2 HOSPITALS

The availability of retrospective data from potassium (K+) analyses fr om two hospitals, one using serum and the other plasma for electrolyte measurements, offered us the possibility to investigate the effect of blood platelet count on serum and plasma K+ concentrations. A weak co rrelation between plasma K+ and platelet count was observed. The in vi tro increase of serum K+ in proportion to the platelet count has clini cal significance in conditions, where it may impede the detection of a n underlying true K+ disorder. Nomograms and correction factors, based on the correlation between platelet count and serum K+, have been sug gested also in some recent reports. In the present study unselected ro utine patient data was used as source data. The effect of platelet cou nt on the concentration of K+ in serum was lower than reported in prev ious studies, as indicated by the regression analysis. An increase of 1000 x 10(9)/1 in the blood platelet count would cause an increase of about 0.7 mmol/l in the serum K+ concentration (p < 0.0001, r = 0.155) . The weak correlation between platelet count and serum K+ does not su pport the application of platelet-count-based correction of serum K+ l evel in thrombocytosis. The laboratory should notify the clinician of the significance of the in vitro increase of serum K+ caused by increa sed platelet count. K+ should be measured from plasma in such cases.