A patient comes with increased aPTT and PT with no bleeding tendency. Even at surgery he did not have increased bleeding. Which factor is deficient-

**Core Concept**
The patient's presentation suggests a coagulation disorder, with increased activated partial thromboplastin time (aPTT) and prothrombin time (PT) in the absence of bleeding tendency. This scenario is indicative of a factor deficiency that primarily affects the intrinsic pathway of coagulation.

**Why the Correct Answer is Right**
In the intrinsic pathway, factor VIII plays a crucial role in the conversion of factor X to factor Xa, which ultimately leads to thrombin formation and clotting. Deficiency of factor VIII would result in increased aPTT, as the intrinsic pathway is impaired. However, since factor VIII is also involved in the common pathway, the PT would also be affected. Notably, patients with mild factor VIII deficiency may not exhibit bleeding symptoms, especially if the deficiency is mild. In such cases, the patient may not have increased bleeding during surgery.

**Why Each Wrong Option is Incorrect**
* **Option A:** Factor XIII deficiency would primarily affect the stability of the clot, leading to delayed bleeding. The patient's aPTT and PT would not be significantly increased.
* **Option B:** Factor VII deficiency would primarily affect the extrinsic pathway, leading to increased PT. The aPTT would not be significantly increased.
* **Option C:** Factor IX deficiency would also affect the intrinsic pathway, but it is less likely to cause significant prolongation of aPTT compared to factor VIII deficiency.

**Clinical Pearl / High-Yield Fact**
Factor VIII deficiency (Hemophilia A) is an X-linked recessive disorder, predominantly affecting males. It is essential to consider this diagnosis in patients with increased aPTT and PT in the absence of bleeding tendency, especially if there is a family history of similar cases.

**Correct Answer:** C.