D-Dimer and DIC

The D-Dimer Test is an important tool for the diagnosis of pathological thrombosis such as Deep Vein Thrombosis (DVT) and Pulmonary Embolism(PE). Being able to identify patients at risk of these cardiovascular diseases can lead to prompt intervention with anticoagulant therapy preventing long term damage or death.
However the D-Dimer can also be used to help diagnose another coagulaopathy, Dessiminated Intravscular Coagulation. Basically something (ie trauma, septicaemia) triggers the coagulation system to initiate clotting. Tiny thrombi are then formed, blocking off the microcirculation and causing red blood cells to fragment, leading to organ dysfunction and anemia.
Unlike DVT and PE though, DIC is not a single entity, but a complex syndrome that has many different causes.
To help determine if a patient has DIC, The Subcommittee on DIC of the International Society on Thrombosis and Haemostasis (ISTH) developed a point system to help determine if "overt" DIC is present:

1. platelet count (more than 100 = 0; less than 100 = 1; less than 50 = 2)

2. elevated fibrin degradation products (FDP) (no increase = 0; moderate increase= 2; strong increase= 3)

3. Prothrombin Time (PT) upper limit of ref. range ( less than 3 secs = 0; more than 3 secs = 1; more than 6 sec. = 2)

4. fibrinogen level ( more than 100 mg/dl = 0; less than 100 mg/dl = 1)

Score of 5: compatible with overt DIC
(Taylor FB Jr, Toh CH, Hoots WK, et al, and the Scientific Subcommittee on Disseminated Intravascular Coagulation (DIC) of the International Society on Thrombosis and Haemostasis (ISTH). Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation. Thromb Haemost. 2001;86:1327-1330.)
Notably absent from this list is the presence of schistocytes, red cells fragmented from circulating through the microthrombi blocking capillaries.
Platelet counts and PT are standard lab tests. Fibrinogen testing is not. As for elevated FDP, this too was, and still is, not a standard lab test, especially in smaller labs. The FDP test is used to measure the amount of fibrinolysis (breakdown of fibrin) present. It makes sense that in DIC there will be an abnormal amount of fibrin being formed, and at the same time an abnormal amount of fibrinolysis taking place. But one test that can be used to measure fibrinolaysis is the D-Dimer test. An increased D-Dimer test may be used to determine if there is an increased level of elevated fibrin degradation products. However, other conditions can cause an increased D-Dimer, and it is up to the lab to determine what level of D-Dimer will be used as the cutoff to be used in the ISTH grading system mentioned above.
For further information refer to :
Wada H, Gabazza EC, Asakura H, et al. Comparison of diagnostic criteria for disseminated intravascular coagulation (DIC): diagnostic criteria of the International Society of Thrombosis and Hemostasis (ISTH) and of the Japanese Ministry of Health and Welfare for overt DIC. Am J Hematol. 2003;74:17-22.
So in conclusion; the ISTH has a score to determine if DIC is present, the D-dimer can be used once a cutoff level has been determined for the method used, and the presence of schistocytes cannot be used to diagnose DIC.