Temperature effects in FP and DHS. (A) Test for pseudohyperkalemia. From the original FP proposita and a representative affected individual of the previously mapped DHS family, whole heparinized blood was stored at room temperature for up to 6 hours before centrifugation, separation of the plasma, and estimation of K. Key, to both panels: •, FP; ○, DHS; □, normals (error bars, A, denote mean ± 2 SEM, n = 22). Only in FP does the K rise with time at this temperature. (B) OBR K influx versus temperature in the same three cases. In FP (•) the OBR flux is marginally greater than normal at 37°C, but shows the shallow slope in the interval 37° to 20°C characteristic of this family, while in DHS, the flux at 37°C is significantly greater than normal (consistent with the frank hemolysis) and shows a temperature profile which is parallel to normal.