**Question:** Which among the following is seen in antiphospholipid antibody syndrome?

A. Thrombocytopenia
B. Thrombosis
C. Proteinuria
D. Hematuria

**Core Concept:** Antiphospholipid antibody syndrome (APS) is an autoimmune disorder characterized by the production of antiphospholipid antibodies, which interfere with the normal coagulation process. APS is classified into primary (idiopathic) and secondary (associated with another condition, such as systemic lupus erythematosus).

**Why the Correct Answer is Right:** Thrombosis (B) is a significant complication seen in antiphospholipid antibody syndrome. The antiphospholipid antibodies interfere with the normal coagulation process, leading to increased blood clot formation (thrombosis) in various vessels, particularly in the small and medium-sized vessels.

**Why Each Wrong Option is Incorrect:**

A. Thrombocytopenia (A) is a decrease in platelet count, which may occur in APS but is not as common or specific as thrombosis.

C. Proteinuria (C) and hematuria (D) are renal complications associated with other conditions like lupus nephritis or vasculitis, not directly related to antiphospholipid antibodies.

**Clinical Pearl:** The antiphospholipid syndrome is associated with a hypercoagulable state, leading to a wide variety of clinical manifestations. A high index of suspicion is essential for the diagnosis of APS, given its potential overlap with other conditions like systemic lupus erythematosus or deep vein thrombosis. A thorough clinical history and examination, along with appropriate laboratory tests, will help in diagnosing the condition.