Prolongation of Every Coagulation Test in Sepsis
A 68-year-old woman is in the intensive care unit on day 2 of gram-negative urosepsis. Her platelet count was 210 x 10^9/L four days ago and is now 58 x 10^9/L. PT is 20.1 seconds (reference 11.5 to 14.5), INR 1.75, aPTT 62 seconds (reference 25 to 35), fibrinogen 88 mg/dL (reference 200 to 400), and D-dimer 4800 ng/mL fibrinogen-equivalent units. The peripheral smear, which the hematology fellow reviews because of a flag on the analyzer, shows 2 to 3 schistocytes per high-power field. She has a triple-lumen catheter and has been receiving subcutaneous heparin 5000 units every 8 hours as prophylaxis. Alanine aminotransferase is 55 U/L and total bilirubin is 1.4 mg/dL.
1. Is this overt disseminated intravascular coagulation? Score it explicitly.
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Yes. Using the ISTH scoring system for overt DIC, which is appropriate here because the patient has a condition known to cause DIC (sepsis):
- Platelet count 58 x 10^9/L, which is below 100 but above 50: 1 point.
- D-dimer 4800, a strong increase: 2 points.
- PT prolonged by about 5 to 7 seconds over the midpoint of the reference interval, that is, over 3 seconds but under 6: 1 point. Using the upper reference limit of 14.5, the prolongation is 5.6 seconds, so the result sits at the boundary and would score 1 to 2 points depending on which convention the laboratory uses.
- Fibrinogen 88 mg/dL, below 100: 1 point.
A total of 5 or more is required for overt DIC, and this is at least 5. The schistocytes and the falling platelet count over four days support a microangiopathic, consumptive process rather than dilution.
The answer is not a diagnosis by numbers alone, though. The underlying cause is being treated, and the score should be repeated with serial testing rather than acted on once.
2. The team asks whether the subcutaneous heparin explains the aPTT of 62 seconds. How would you sort out the heparin contribution from the coagulopathy?
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Prophylactic subcutaneous heparin can prolong the aPTT in some patients, but it cannot produce this whole picture. Heparin does not lower fibrinogen to 88 mg/dL, does not drop the platelet count from 210 to 58 over four days, and does not generate D-dimer at 4800 or schistocytes on the smear. So even if heparin is contributing to the aPTT, there is a second process present.
To separate them:
- Run a thrombin time and a reptilase time. If the thrombin time is prolonged but the reptilase time is normal, heparin (or a direct thrombin inhibitor) is present. If both are prolonged, a fibrinogen problem such as the low fibrinogen seen here is the likely cause.
- A heparin anti-Xa level quantifies the heparin effect directly.
- A mixing study is of limited value in the face of overt consumption; interpret it with caution.
Remember too that the prophylactic dose is a treatment question, not just a laboratory one: in a patient with overt DIC, subcutaneous heparin is usually continued for venous thromboembolism prophylaxis unless there is active bleeding.
3. She is not actively bleeding. What blood component support, if any, would you recommend today, and what thresholds would change if she began to bleed or needed a line change?
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Without bleeding, the guiding principle is to treat the cause, not the numbers. The sepsis is already being treated, and transfusing components into a consumptive state tends to be short-lived and can add volume and reaction risk.
- Platelets: prophylactic transfusion is usually reserved for counts below 10 x 10^9/L. Her count is 58 x 10^9/L, so no transfusion now.
- Fibrinogen: cryoprecipitate is generally reserved for a fibrinogen below about 100 to 150 mg/dL in a patient who is bleeding or about to undergo a procedure. At 88 mg/dL with no bleeding, observe and recheck.
- Fresh frozen plasma: not indicated without bleeding or an imminent procedure, because it will be consumed rapidly and adds volume.
If she started bleeding, the thresholds shift: keep platelets above 50 x 10^9/L, keep fibrinogen above 100 to 150 mg/dL with cryoprecipitate, and give plasma for prolonged PT and aPTT with clinical bleeding. Before a line change or other procedure, treat to those same targets. Repeat the platelet count, PT, aPTT, and fibrinogen every 6 to 12 hours while she is unstable, and reassess the score.