Laboratory Testing for Patients with Severely Elevated INR and COVID-19
For patients with severely elevated INR and COVID-19, comprehensive coagulation monitoring should include D-dimer, prothrombin time (PT), platelet count, and fibrinogen (in decreasing order of importance). 1
Essential Laboratory Tests
D-dimer: Most important marker for risk stratification and prognosis in COVID-19 patients. Markedly elevated D-dimer (3-4 fold increase above normal) is associated with increased mortality and need for critical care support. 1
Prothrombin Time (PT): Should be measured and reported in seconds rather than INR for better sensitivity to detect subtle changes. PT is typically prolonged in non-survivors (15.5 seconds vs. 13.6 seconds in survivors). 1
Platelet Count: Important for monitoring thrombocytopenia, which is associated with a five-fold increased risk of severe COVID-19. Lower platelet counts correlate with mortality. 1
Fibrinogen: Recommended for comprehensive coagulation assessment, particularly in critically ill patients. Decreasing fibrinogen levels in COVID-19 patients are associated with poor outcomes. 1
Monitoring Frequency
Initial Assessment: All four parameters (D-dimer, PT, platelet count, fibrinogen) should be measured at presentation. 1
Hospitalized Patients: Monitor these parameters at least twice daily to identify worsening coagulopathy. 1
Critical Phase: For critically ill patients, D-dimer should be monitored every 24-48 hours during the first 7-10 days when most thrombotic events occur. 1
Additional Considerations
Anti-Xa Activity: For patients receiving unfractionated heparin, anti-Xa activity monitoring is preferred over aPTT, as aPTT may be affected by the inflammatory state of COVID-19. 1
Disseminated Intravascular Coagulation (DIC): Development of DIC on day 4 was observed in 71.4% of non-survivors compared to only 0.6% of survivors, making regular monitoring crucial. 1
Interpretation Caveats: When interpreting results, account for underlying conditions (e.g., liver disease) or medications (e.g., anticoagulants) that may affect these parameters. 1
Clinical Implications of Laboratory Results
Admission Criteria: Consider hospital admission for patients with markedly raised D-dimers (3-4 fold increase), prolonged PT, platelet count <100 × 10^9/L, or fibrinogen <2.0 g/L. 1
Treatment Escalation: If these parameters worsen during hospitalization, more aggressive critical care support and consideration of experimental therapies may be warranted. 1
Anticoagulation Management: Laboratory parameters should guide anticoagulation therapy, particularly in patients with SIC (sepsis-induced coagulopathy) score ≥4 or D-dimer >6-fold of upper limit of normal. 1
Common Pitfalls to Avoid
INR vs. PT Ratio: Subtle changes in coagulation may not be detected if PT is reported as INR rather than in seconds. INR is not the same as PT ratio. 1
Relying on Single Parameters: No single parameter should be used to guide management decisions. The complete coagulation profile should be considered. 1
Overlooking Temporal Changes: There is a temporal relationship between disease progression and thrombotic/hemorrhagic risks, with thrombotic events occurring around day 7 and hemorrhagic events around day 11 of hospitalization. 1
Missing Heparin Resistance: COVID-19 patients frequently develop heparin resistance due to high factor VIII and fibrinogen levels, requiring anti-Xa monitoring rather than aPTT for patients on unfractionated heparin. 1