Plasma Hemoglobin: Potential Sources.

Plasma hemoglobin(Hb) is a measure of circulating red blood cell(RBC) destruction and is considered to be the basic indicator of intravascular hemolysis. We have examined the effects of splenectomy on levels of plasma Hb and circulating RBC-derived vesicles in patients with thalassemia intermedia (TI) and compared the results to patients with sickle cell anemia (SCA). Plasma Hb levels in splenectomized patients with TI were 48.5 ± 3.7 mg/ml (5)(Mn ± SEM)(No.of patients) and vesicle levels were 11.29 ± 1.12 x 10 ³ /ul blood (9). In contrast, plasma Hb levels in patients with SCA were (14.52 ± 3.29)(21) and vesicle levels were 13.2 ± 2.57)(34). Plasma Hb levels and vesicle levels are closely associated in TI and SCA (r=0.79, p=0.01[9]; r=0.58, p=0.006[21] respectively). The finding that plasma Hb levels in patients with TI and SCA, both asplenic, differ in their relationships to corresponding and similar vesicle levels, suggests that other hemolytic factors may contribute to plasma Hb levels. Of importance would be intramedullary hemolysis which is considerable in TI. Vesiculation, which may occur with intramedullary hemolysis does not appear to contribute to circulating vesicle levels. The ratio of plasma Hb levels to vesicle counts would be a marker to distinguish intramedullary hemolysis from intravascular hemolysis. Similar considerations may apply to measures of lactic dehydrogenase (LDH) which is also an indicator of RBC destruction and intravascular hemolysis. The findings suggest that the contribution of intramedullary hemolysis as well as the contribution of intravascular hemolysis should be considered in measurements of plasma Hb.