DIC

Summary

Disseminated Intravascular Coagulation (DIC) is an acquired syndrome of widespread activation of the coagulation cascade inside the small blood vessels. This leads to two problems happening at the same time:

1. Microthrombi → ischemia and organ damage.
2. Consumption of platelets and clotting factors → bleeding from multiple sites.

DIC is always secondary to another illness — most commonly sepsis, trauma, obstetric complications, or malignancy. The hallmark labs are: ↑ PT, ↑ aPTT, ↓ platelets, ↓ fibrinogen, ↑↑ D-dimer, and schistocytes on peripheral smear. Treatment is to fix the underlying cause and provide supportive transfusion of platelets, FFP, and cryoprecipitate as needed.

Definition

• DIC = a consumptive coagulopathy in which the coagulation system is activated systemically rather than locally.
• The result is simultaneous thrombosis and bleeding — a paradox that defines the disease.
• It is never a primary disease. There is always an underlying trigger.

Two clinical forms:

• Acute (decompensated) DIC — rapid onset, bleeding-dominant. Seen in sepsis, trauma, obstetric emergencies.
• Chronic (compensated) DIC — slow onset, thrombosis-dominant, labs may be near-normal. Classic in solid malignancies (Trousseau syndrome).

Etiology

DIC is triggered by any condition that releases tissue factor or otherwise activates coagulation systemically. The four classic categories — memorize them:

• Sepsis (most common cause overall) — especially gram-negative bacteria (LPS/endotoxin), Neisseria meningitidis (purpura fulminans, Waterhouse–Friderichsen).
• Trauma — major trauma, burns, crush injury, head injury (brain is rich in tissue factor).
• Obstetric — abruptio placentae, amniotic fluid embolism, retained dead fetus, septic abortion, HELLP, severe pre-eclampsia.
• Malignancy — acute promyelocytic leukemia (APL, AML-M3) is the classic; mucin-secreting adenocarcinomas (pancreas, prostate, lung, GI) cause chronic DIC.

Other triggers: acute pancreatitis, snake envenomation, severe transfusion reactions (ABO-mismatch), massive hemolysis, heat stroke, giant hemangioma (Kasabach–Merritt).

Mnemonic for Causes

Pathophysiology

Think of DIC as one trigger → four downstream events:

1. Massive tissue factor (TF) release into the circulation (from endotoxin, damaged tissue, placenta, tumor cells, or APL granules).
2. Widespread activation of the extrinsic and common pathway → diffuse microthrombi in small vessels → ischemic injury (kidney, lung, skin, brain).
3. Consumption of platelets, fibrinogen, and clotting factors (II, V, VIII) → bleeding from venipuncture sites, GI tract, GU tract, surgical wounds.
4. Secondary fibrinolysis — plasmin breaks down the fibrin clots → release of fibrin degradation products (FDPs) and D-dimer; FDPs further inhibit platelet function and worsen bleeding.

The RBCs are mechanically sheared as they pass through the fibrin mesh → schistocytes and microangiopathic hemolytic anemia (MAHA).

View the full DIC pathophysiology diagram.

Clinical Features

The patient looks sick — and clinical signs reflect the two opposing processes: bleeding + microvascular thrombosis.

Bleeding (usually dominant in acute DIC):

• Oozing from venipuncture sites, IV lines, and surgical wounds (very characteristic).
• Petechiae, purpura, ecchymoses; mucosal bleeding (gums, epistaxis).
• GI bleeding, hematuria, intracranial hemorrhage.
• In meningococcemia → purpura fulminans (large hemorrhagic skin necrosis).

Thrombosis / end-organ ischemia:

• Kidney: acute kidney injury, oliguria.
• Lung: ARDS, dyspnea, hypoxemia.
• Skin: digital gangrene, acral cyanosis.
• CNS: confusion, coma.
• Adrenal: bilateral hemorrhagic necrosis → Waterhouse–Friderichsen syndrome (shock + adrenal insufficiency).

Diagnosis

The diagnosis is clinical + laboratory. There is no single confirmatory test. Suspect DIC in any unstable patient (sepsis, trauma, OB emergency, cancer) with new bleeding or multi-organ dysfunction.

Open the full DIC laboratory reference table for a side-by-side review.

Schistocytes on peripheral smear — fragmented RBCs are the visual signature of MAHA.

Differential Diagnosis

Several conditions cause low platelets and/or prolonged coagulation tests. Use the lab pattern to separate them:

Key distinguishing points:

• vs. Liver failure: liver disease also lowers fibrinogen and prolongs PT/PTT, but Factor VIII is normal or high (made by endothelium, not liver). In DIC, Factor VIII is low.
• vs. TTP/HUS: both have schistocytes and ↓ platelets, but PT/PTT and fibrinogen are normal.
• vs. Vitamin K deficiency / warfarin: platelets and fibrinogen are normal; no schistocytes.
• vs. ITP: isolated thrombocytopenia; PT, aPTT, fibrinogen all normal.

Reference: Coagulopathy comparison table (vWD, ITP, TTP-HUS, DIC).

Management

The single most important step is to treat the underlying cause. DIC will not resolve until the trigger is controlled.

1. Treat the trigger:

• Sepsis → broad-spectrum antibiotics + source control.
• Obstetric DIC → deliver the fetus / evacuate the uterus.
• APL (M3 leukemia) → start ATRA (all-trans retinoic acid) immediately — even before genetic confirmation.
• Trauma → surgical hemostasis, warming, correct acidosis.

2. Supportive blood-product transfusion (only if actively bleeding or before procedure):

• Platelets → if platelets < 20 × 10⁹/L, or < 50 with bleeding.
• Fresh Frozen Plasma (FFP) → replaces all clotting factors when PT/aPTT prolonged.
• Cryoprecipitate → if fibrinogen < 100 mg/dL (rich in fibrinogen, factor VIII, vWF, XIII).
• Packed RBCs → for symptomatic anemia / active hemorrhage.

3. Anticoagulation (controversial, selective use):

• Low-dose heparin may be used in chronic, thrombosis-dominant DIC (e.g., Trousseau syndrome with cancer).
• Avoid heparin in acute bleeding-dominant DIC.

Complications & Prognosis

• Multi-organ failure (kidney, lung/ARDS, liver, CNS) — leading cause of death.
• Massive hemorrhage — intracranial, GI, pulmonary.
• Purpura fulminans and digital/limb gangrene.
• Waterhouse–Friderichsen syndrome — adrenal hemorrhage → acute adrenal insufficiency (classically meningococcemia).
• Death — mortality is high (30–50%), driven by the underlying disease.

Key Points for Exams – نقاط مهمة للامتحانات

• DIC = simultaneous bleeding + thrombosis. Always secondary to another illness.
• Top causes: Sepsis (gram-negative), Trauma, Obstetric (abruptio, AFE), Malignancy (APL).
• Lab signature: ↑ PT, ↑ aPTT, ↓ platelets, ↓ fibrinogen, ↑↑ D-dimer, schistocytes. Bleeding time is also prolonged — DIC is the only condition that abnormalizes all four screening tests.
• D-dimer is the most sensitive lab for DIC.
• Factor VIII low in DIC, normal/high in liver disease — the key board distinction.
• APL (AML-M3) with Auer rods → treat immediately with ATRA to prevent fatal DIC.
• Meningococcemia → purpura fulminans + DIC + Waterhouse–Friderichsen.
• Treatment = fix the underlying cause first; transfuse platelets / FFP / cryoprecipitate only if actively bleeding.
• Heparin is reserved for chronic, thrombosis-predominant DIC (e.g., Trousseau syndrome).