In the medical field, the term "PTA" stands for plasma thromboplastin antecedent, according to Dictionary.com. PTA is commonly referred to as factor XI. This is a specialized protein that helps blood to clot, reports WebMD.
A lack of PTA, or factor XI, leads to hemorrhagic tendency. Some individuals have a genetic bleeding disorder caused by low levels and activity of factor XI, according to WebMD. This disorder leads to prolonged bleeding after deep wounds such as those caused by surgery or trauma. Individuals, who can be either male or female, inherit factor XI deficiency autosomally.
Another common medical term for factor XI deficiency is hemophilia C, according to Encyclopædia Britannica.