A blood test to determine the number of leukocytes present is called:

A) RBC.
B) WBC.
C) Hct.
D) PTT.

A blood test to determine the number of leukocytes present refers to the white blood cells (WBC). Therefore, the best choice is B. RBC (red blood cells) and Hct (hematocrit) are tests that determine the levels of red blood cells in the blood, and PTT (partial thromboplastin time) is a test that assesses blood clotting ability.