Which diseases can cause clotting of the continuous venovenous hemodialysis (CVVHD) circuit?

Diseases Causing Clotting in CVVHD Circuits

COVID-19 is the most prominently documented disease causing increased clotting in continuous venovenous hemodialysis (CVVHD) circuits, driven by severe hypercoagulability from elevated factor VIII, fibrinogen, and D-dimers. 1, 2

Primary Disease: COVID-19

The most recent and highest-quality evidence identifies COVID-19 as a major cause of CVVHD circuit clotting. The mechanism involves intense systemic inflammation that triggers:

• Contact activation and complement system hyperactivity leading to excessive thrombin generation 1
• Elevated coagulation factors: Factor VIII (median 273 vs 166 IU/dL in non-clotting patients), fibrinogen (5.6 vs 4.9 g/L), and D-dimers (2654 vs 1351 ng/mL) 2
• Circuit clotting occurs in 33.5% of hemodialysis patients within 4 weeks of testing positive 2

Management Approach for COVID-19 Patients:

• Increase heparin doses beyond routine anticoagulation 1
• Consider therapeutic anticoagulation if evidence of circuit clots develops 1
• Monitor factor VIII, fibrinogen, and D-dimer levels as predictors of clotting risk 2
• Consider complement inhibitors or contact pathway inhibitors as adjunctive therapy 1

Other Hypercoagulable Diseases

Cancer (Active Malignancy)

Active cancer disease increases circuit clotting risk, particularly:

• Genitourinary tumors (OR 1.83) 3
• Patients with tumor evidence have higher clotting rates than those without (OR 0.44 for no tumor) 3
• Mechanism: tumor-associated hypercoagulability, direct vascular compression, and chemotherapy effects 4, 5, 4

Inherited Thrombophilias

While these primarily cause cerebral venous thrombosis, they create systemic hypercoagulability affecting extracorporeal circuits:

• Antithrombin III deficiency 5
• Protein C deficiency (OR 11.1 for thrombosis) 5
• Protein S deficiency 5
• Factor V Leiden 5

Antiphospholipid Syndrome

Creates acquired hypercoagulability through:

• Changes in blood composition (Virchow triad) 5
• Systemic prothrombotic state affecting all vascular beds including extracorporeal circuits

Heparin-Induced Thrombocytopenia (HIT)

Critical consideration: HIT is more common in inflammatory conditions and creates paradoxical thrombosis despite thrombocytopenia 1. This is particularly relevant since heparin is the standard anticoagulant for CVVHD circuits.

Clinical Algorithm for Assessment

When encountering circuit clotting:

1. First, check for COVID-19 - Test if not already done; review timing of positive test (risk highest within 4 weeks) 2

2. Obtain coagulation panel:

   • Factor VIII (>273 IU/dL suggests high risk) 2
   • Fibrinogen (>5.6 g/L suggests high risk) 2
   • D-dimers (>2654 ng/mL suggests high risk) 2
   • INR (lower INR paradoxically associated with more clotting) 3
   • Platelet count (for HIT screening) 1

3. Screen for active malignancy - particularly genitourinary cancers 3

4. Consider inherited thrombophilias if young patient or family history 5

Common Pitfalls

• Do not assume standard prophylactic anticoagulation is adequate in COVID-19 patients - multiple reports show "failure" of standard dosing 1
• Do not overlook HIT when increasing heparin doses - monitor platelet counts closely 1
• Do not ignore lower INR values - paradoxically associated with increased clotting in cancer patients on CVVHD 3
• Avoid aPTT confounding - conditions like liver impairment or lupus anticoagulant may show therapeutic aPTT with subtherapeutic anticoagulant levels 1