**Core Concept**
Fibrin degradation products (FDPs) are generated during the breakdown of fibrin clots by plasmin. They are used as markers of fibrinolysis and coagulation activation.

**Why the Correct Answer is Right**
FDPs, particularly D-dimer, are used in the diagnosis of thrombotic disorders, such as deep vein thrombosis (DVT) and pulmonary embolism (PE). Elevated levels of FDPs indicate that a clot has been broken down by plasmin, and are often used in conjunction with clinical assessment and imaging studies to confirm the diagnosis. D-dimer is a specific type of FDP that is formed when cross-linked fibrin is broken down by plasmin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because FDPs are not primarily used in the detection of infections. While infections can lead to the activation of coagulation and the formation of clots, FDPs are not a direct indicator of infection.
**Option B:** This option is incorrect because FDPs are not used in the detection of cancer. While cancer can lead to the activation of coagulation and the formation of clots, FDPs are not a specific marker for cancer.

**Clinical Pearl / High-Yield Fact**
D-dimer levels are elevated in conditions that involve the breakdown of fibrin clots, but are not specific to thrombotic disorders. A high D-dimer level can also be seen in conditions such as pregnancy, recent surgery, and trauma.

**Correct Answer: D. D-dimer**