Haemophilia is a X-linked (Sex-linked) recessive hereditary disease of the blood coagulation with greatly prolonged coagulation time.
There is bleeding in joints and tissues forming haematoma, chronic haemophilic arthritis and anaemia.

Types of haemophilia :
1. Haemophilia A :- classical haemophilia or true haemophilia due to deficiency of clotting factor VIII.
2. Haemophilia B or Christmas disease :- due to deficiency of factor IX.

Inheritance: Both haemophilia A and haemophilia b are inherited sex linked recessive character, but are genetically different. Eid nearly always effects the males. The sons of a haemophilic man do not suffer from haemophilia and do not transmit. The daughters of a haemophilic man carry the trait and transmit the disease. However, a hemophilic man marries career female, then only there is chance of a female to be hemophilic.

Laboratory diagnosis:

1. Whole blood clotting time- prolonged. In severe cases may be more than 90 minutes and in mild cases 10-20 minutes.
2. Bleeding time- normal.
3. Platelet count and morphology- normal.
4. Tourniquet test- normal.
5. Prothrombin time (PT) (one stage)- normal.
6. Activated partial thromboplastin time (APTT)- prolonged.
7. Thrombin clotting time- normal.
8. Thromboplastin generation test- (i) Reduced in haemophilia A, and (ii) Normal in haemophilia B.
9. Factor VIII. Deficiency in haemophilia A and also in von Willebrand,s disease.
10. Factor IX. Deficiency in haemophilia B, and also in new born infants, liver disease and vitamin K deficiency.
11. Routine Blood Test- Shows anaemia.