Hematocrit

Hematocrit (haematocrit, HCT, HCr, Ht) is the proportion of blood volume that is occupied by red blood cells. The hematocrit is normally between 0.40-0.51 in men and 0.36-0.47 in women.

In analysis of PET studies, hematocrit is often needed in conversion of blood radioactivity concentrations to plasma concentrations, and vice versa.

Regional hematocrit

Copper-62-labelled human serum albumin-dithiosemicarbazone, [⁶²Cu]-HSA-DTS, can be used as a plasma-pool imaging agent, and oxygen-15 labelled carbon monoxide, [¹⁵O]CO, as a erythrocyte imaging agent. Together these PET tracers can be used to determine the regional hematocrit and regional/large-vessel hematocrit ratio.

Mean regional cerebral hematocrit was 38.3 ± 3.45 % in 12 normal volunteers, and mean cerebral/large-vessel hematocrit ratio was 0.88 ± 0.06 (Okazawa et al. 1996). In the same study, in patients with cerebrovascular disease, regional cerebral hematocrit was significantly lower.

This cerebral/large-vessel hematocrit ratio is close to the value 0.85 (Grubb et al. 1973) which is used widely in the literature, e.g. in determination of the blood volume using [¹⁵O]CO PET, but clearly higher than the value 0.69 determined from nine subjects using [¹¹C]methyl-albumin and [¹¹C]CO (Lammertsma et al. 1984).

References:

Grubb RL Jr, Phelps ME, Ter-Pogossian MM. Regional cerebral blood volume in humans. X-ray fluorescence studies. Arch Neurol 1973; 28: 38-44.

Lammertsma AA, Brooks DJ, Beaney RP, Turton DR, Kensett MJ, Heather JD, Marshall J, Jones T. In vivo measurement of regional cerebral haematocrit using positron emission tomography. J Cereb Blood Flow Metab 1984; 4: 317-322.

Okazawa H, Yonekura Y, Fujibayashi Y, Yamauchi H, Ishizu K, Nishizawa S, Magata Y, Tamaki N, Fukuyama H, Yokoyama A, Konishi J. Measurement of regional cerebral plasma pool and hematocrit with copper-62-labeled HSA-DTS. J Nucl Med 1996; 37: 1080-1085.