From the Guidelines
Yes, a D-dimer can be elevated in severe pneumonia, with studies suggesting that markedly elevated D-dimers are associated with increased mortality and severity of illness. D-dimer is a fibrin degradation product that indicates active blood clotting and subsequent fibrinolysis, and it's often elevated in inflammatory conditions beyond just blood clots. In severe pneumonia, the intense inflammatory response can activate the coagulation cascade, leading to increased fibrin formation and breakdown, resulting in elevated D-dimer levels. This elevation occurs because pneumonia, especially when severe, creates a systemic inflammatory state that disrupts the normal balance between clotting and anticoagulation mechanisms in the body.
Key Points to Consider
- A study published in the Journal of Thrombosis and Haemostasis in 2020 found that a D-dimer ≥0.5 mg/L was noted in 46.4% of patients with COVID-19, with about 60% of patients with severe illness having elevated D-dimers 1.
- Another study published in Anaesthesia in 2021 found that baseline D-dimers level above the upper limit of normal is associated with critical illness, thrombosis, acute kidney injury, and death, and that a D-dimers level > 5 mg/mL is associated with a positive predictive value of 50% for thrombotic complications 1.
- The degree of elevation may correlate with disease severity and can sometimes be used as a prognostic marker.
- Clinicians should be aware that while elevated D-dimer in pneumonia patients may suggest possible complications like pulmonary embolism, the elevation may simply reflect the severity of the infection and inflammation rather than indicating a thromboembolic event.
- Therefore, D-dimer results in pneumonia patients should be interpreted cautiously and in the context of other clinical findings.
Implications for Clinical Practice
- Elevated D-dimer levels should prompt further evaluation and consideration of thromboprophylaxis or therapeutic anticoagulation in patients with severe pneumonia.
- The use of D-dimers for diagnosing thrombosis is noteworthy, but the positive predictive value is low in many clinical settings where venous thromboembolism incidence is low.
- However, in severe pneumonia patients with a high burden of thrombotic complications, a D-dimers level > 5 mg/mL is associated with a remarkably high thrombotic risk, with a positive predictive value of at least 40–50%.
From the Research
D-Dimer Levels in Severe Pneumonia
- D-dimer levels are elevated in patients with community-acquired pneumonia (CAP) and increase with the severity of the disease 2.
- Studies have shown that D-dimer levels are higher in patients with severe CAP compared to those with non-severe CAP 3, 2, 4.
- A D-dimer level less than 500 ng/mL may identify patients at low risk for complications and mortality 5, 3.
- Elevated plasma D-dimer levels in adult CAP patients are associated with an increased inflammatory reaction and lower survival 4.
Association with Inflammatory Reaction and Mortality
- D-dimer levels have a positive correlation with serum inflammatory markers (WBC, hs-CRP, PCT) and prognostic indexes (ICU admission and 30-day mortality) 4.
- The area under the receiver operating characteristic curve (AUC) of D-dimer for predicting ICU admission and/or 30-day mortality is 0.880 (95% CI 0.823 to 0.936) 4.
- D-dimer levels are superior to hs-CRP and PCT in predicting 30-day mortality and/or ICU admission according to AUCs of the ROC curves 4.
Diagnostic Value of D-Dimer
- Plasma D-dimer levels are increased in patients with pneumonia, but the test is not useful in the differential diagnosis between pneumonia and pulmonary embolism due to overlapping values 6.
- The sensitivity and specificity of plasmatic D-dimer in the emergency diagnosis of pulmonary embolism are 92% and 71%, respectively 6.