Question

A woman brings her 13 year old son to the pediatrician’s office. The boy’s problems go back to the neonatal period, when he bled unduly after circumcision. When his deciduous (baby) teeth first erupted, he bit his lower lip, and the wound oozed for 2 days. As he began to crawl and walk, bruises appeared on his arms & legs. Occasionally he would sustain a nosebleed without having had an obvious injury. By the time he was 3 years of age, his parents became aware that occasionally he would have painful swelling of a joint (knee, shoulder or wrist) but his fingers & toes seemed spared. The joint swelling would be accompanied by exquisite tenderness; the swelling would subside in 2-3 days. The patient’s mother states that when her son was a baby, she noted what appeared to be blood in his stool, and the boy tells the pediatrician that twice his urine appeared red for 1-2 days. Anxiously the patient’s mother relates that her brother & her maternal uncle both had similar problems & were thought to be “bleeders”. There is no further family history of bleeding and there is no parental consanguinity (i.e. the patient’s parents are not blood relatives). Examination of this boy reveals the presence of ecchymosis and the inability to fully flex or extend his elbows. A panel of four tests is ordered with instructions to extend testing as appropriate. The four tests are a (1) platelet count, (2) prothrombin time, (3) partial thromboplastin time and (4) bleeding time. The patient’s platelet count was found to be 260,000/microliter (normal is 150,000-300,000)

a) What is the role of platelets in hemostasis?

b) What purpose is served by drawing blood into a solution of sodium citrate? What is the purpose of adding a solution of calcium chloride? Does the prothrombin time measure the intrinsic or extrinsic pathway of coagulation?

c) What mechanisms might cause the prothrombin time to be abnormally long?

d) With the given data, can you guess in general the site of the clotting abnormality in this patient?

e) What clotting factors participate in the early steps of the intrinsic pathway of thrombin formation?

Answer 1

a) What is the role of platelets in hemostasis?

- adhesion, activation and aggregation, which are triggered upon tissue injury, and these actions stimulate the coagulation factors and other mediators to achieve haemostasis

b) -What purpose is served by drawing blood into a solution of sodium citrate?

- sodium citrate act as anti coagulant

-remove calcium, which is essential for coagulation.

-What is the purpose of adding a solution of calcium chloride?

- addition of sodium citrate prevents clot formation, inorder to check for prothrombin time, we will add calcium chloride to the centrifugated sediment and the time taken from then to clot formation that is PT.

-Does the prothrombin time measure the intrinsic or extrinsic pathway of coagulation?

- extrinsic and final common pathway

c) What mechanisms might cause the prothrombin time to be abnormally long?

-time taken to form a clot is prolongated

-because of lack of less production of clotting protein

- liver disease, vit K defeciency, coagulation factor defeciency

d) With the given data, can you guess in general the site of the clotting abnormality in this patient?

- intrinsic pathway is the abnormality

e) What clotting factors participate in the early steps of the intrinsic pathway of thrombin formation?

- clotting factors 9, 10, 12