The applicability of blood recalcification time as a laboratory test to assess and thereby regulate heparin anticoagulation was evaluated. Normal values for blood recalcification time ranged from 65 to 135 seconds, with a mean and standard deviation of 99 and 12 seconds, respectively. Duplicate determinations showed a mean variation of 5%. Blood recalcification times increased as a linear function of increasing heparin concentrations in vitro. Comparison with whole-blood clotting times revealed reasonably good correlation between the two tests. For whole-blood clotting times of 20 to 45 minutes the corresponding blood recalcification times were 142 to 212 seconds. The therapeutic range is often considered to be twice the normal range (130-270 seconds). In-vivo study revealed the peak blood recalcification time in the first sample collected 30 minutes after heparin injection, and a progressive decline thereafter to the pre-injection level during the subsequent 4 hours. The blood recalcification time is a simple, precise and clinically useful test to monitor heparin therapy.

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A rapid method for measuring volume distributions of human, calf and goat lymphocytes and their nuclei is described along with the type of quantitation these measurements can provide by computer analysis. The size distribution studies indicate the presence of two populations of lymphocytes and their nuclei irrespective of the cell source. It is suggested that proliferative fractions of various cell populations may be estimated by determining the nuclear volume distribution.