Antithrombin III levels in disseminated intravascular coagulation –
**Core Concept**
Antithrombin III (AT III) is a serine protease inhibitor that plays a crucial role in regulating the coagulation cascade by inhibiting the activity of thrombin and other clotting factors. In disseminated intravascular coagulation (DIC), the levels of AT III are often decreased due to consumption and/or renal loss.
**Why the Correct Answer is Right**
In DIC, the continuous activation of the coagulation cascade leads to the consumption of AT III, which in turn results in a decrease in its plasma levels. This is because AT III is unable to keep up with the high demand to inhibit thrombin and other clotting factors. As a result, the pro-coagulant state in DIC is further exacerbated by the low levels of AT III. The liver is the primary site of AT III production, and in severe cases of DIC, renal failure can also occur, leading to further loss of AT III.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the levels of antithrombin III are not typically increased in DIC. The consumption of AT III in DIC leads to a decrease in its plasma levels.
* **Option B:** This option is incorrect because the levels of protein C are actually decreased in DIC, not increased. Protein C is another serine protease inhibitor that is consumed in DIC, similar to AT III.
* **Option C:** This option is incorrect because the levels of factor VIII are often increased in DIC, not decreased. Factor VIII is a clotting factor that is consumed in DIC, leading to an increase in its plasma levels.
**Clinical Pearl / High-Yield Fact**
In DIC, the decrease in antithrombin III levels is a marker of the severity of the coagulopathy and can be used to monitor the effectiveness of treatment. Low levels of AT III are associated with a poor prognosis and increased risk of thrombotic complications.
**Correct Answer:** D.