Solution:
People that born with hemophilia lack or have a low amount of a clotting factor.
Coagulation factors are proteins necessary for normal blood clotting.
Coagulation factors are found in blood plasma. These factors act with Thrombocytes to clot blood.
However, hemophilia is not a decrease in Thrombocytes but a decrease in coagulation factors due to genetic causes.
Diagnosis includes screening tests and clotting factor analysis. Screening tests are blood tests that show whether the blood is clotting properly. Clotting factor tests can reveal a deficiency of clotting factors in the blood plasma and determine the level of severity of hemophilia.
As the coagulation factors are in Blood plasma, we can conclude that the correct answer is:
BLOOD PLASMA