Laboratory Workup for Hemoptysis with Ground Glass Opacities
For a patient presenting with hemoptysis and ground glass opacities on chest CT, the essential laboratory workup should include: complete blood count with differential (focusing on lymphocyte count and eosinophils), inflammatory markers (C-reactive protein and procalcitonin), and respiratory pathogen testing including viral antigens and nucleic acid detection.
Core Laboratory Tests
Hematologic Studies
- Complete blood count with differential is essential, with particular attention to:
- Total white blood cell count (may be normal or decreased) 1
- Absolute lymphocyte count (critical if <0.8 × 10⁹/L, which warrants repeat testing in 3 days) 1
- CD4 and CD8 T cell counts if lymphocytes are significantly decreased 1
- Eosinophil count (often decreased to 0 × 10⁹/L in viral pneumonias) 1
- Monocyte count (may be increased or normal) 1
Inflammatory Markers
- C-reactive protein (CRP) should be measured, as elevations are commonly seen with ground glass opacities (values ranging from 53.0-170.91 mg/L documented in viral pneumonias) 1
- Procalcitonin helps differentiate bacterial from viral etiologies (elevated in cases with ground glass opacities, typically 0.10-0.45 ng/ml) 1
- Erythrocyte sedimentation rate may provide additional inflammatory assessment 1
Respiratory Pathogen Detection
- Influenza antigens (A, B, and H7N subtypes) via throat swab for rapid screening, though false negative rates are relatively high 1
- Respiratory virus nucleic acid testing is commonly used and more sensitive than antigen testing 1
- Testing should distinguish between viral pneumonias (influenza, parainfluenza, adenovirus, respiratory syncytial virus, rhinovirus, metapneumovirus, coronavirus) and atypical pathogens 1
Additional Laboratory Considerations
Protein and Liver Function
- Total protein, albumin, and globulin levels should be assessed, as hypoproteinemia is documented in patients with ground glass opacities 1
- Liver function tests may reveal reduced function in some cases 1
Recheck Strategy
- Repeat blood counts after 3 days if initial lymphocyte count is <0.8 × 10⁹/L or if CD4/CD8 T cells are significantly decreased 1
Differential Diagnosis Context
The combination of hemoptysis and ground glass opacities requires consideration of multiple etiologies beyond infection 2:
- Viral pneumonias (COVID-19, influenza, cytomegalovirus)
- Alveolar hemorrhage
- Pulmonary infarction
- Vaping-related lung injury
- Pulmonary edema
- Vasculitis or organizing pneumonia 1, 2
Critical Pitfalls to Avoid
- Do not dismiss normal white blood cell counts – viral pneumonias with ground glass opacities frequently present with normal leukocyte counts but decreased lymphocytes 1
- Recheck lymphocyte counts if initially low, as progressive lymphopenia indicates more severe disease 1
- Correlate laboratory findings with imaging patterns – the combination of decreased lymphocytes, elevated CRP, and ground glass opacities strongly suggests viral pneumonia 1
- Consider non-infectious causes when infectious workup is negative, particularly in the context of hemoptysis 2