Can active Covid (Coronavirus disease) infection alter bloodwork results?

COVID-19 Significantly Alters Multiple Blood Parameters

Active COVID-19 infection causes substantial alterations in bloodwork results, including coagulation markers, inflammatory indicators, and hematological parameters that can significantly impact patient morbidity and mortality. 1

Key Blood Alterations in COVID-19

Coagulation Abnormalities

• D-dimer levels: Markedly increased in COVID-19, associated with worse outcomes 1
• Prothrombin time (PT): Prolonged in severe cases 1
• Activated partial thromboplastin time (aPTT): Prolonged in patients with worse outcomes 1
• Fibrinogen: Hyperfibrinogenemia is common 1
• Clot strength: Increased, creating a pro-coagulant profile 1

Inflammatory Markers

• Neutrophil-to-lymphocyte ratio (NLR): Significantly elevated in severe COVID-19; can be used as an independent predictor of disease severity 2
• Platelet-to-lymphocyte ratio (PLR): Higher in severely symptomatic patients 2
• Derived NLR (d-NLR): Elevated in severe cases 2

Hematological Changes

• Lymphocytes: Reduced counts (lymphopenia), particularly in severe cases 1, 2
• Neutrophils: Increased counts in critically ill patients 1
• Red blood cells: Altered size, stiffness, and deformability 1
• Red cell distribution width (RDW): Substantial increases during acute infection 1
• Hemoglobin: Often decreased in severe cases 2

Mechanisms Behind Blood Alterations

1. Endothelial Dysfunction

   • SARS-CoV-2 causes endothelial cell swelling and damage (endotheliitis) 3
   • Inflammatory cytokines shift endothelium to a pro-adhesive and pro-thrombotic state 1
   • Vascular density reduction, especially affecting small capillaries, persists up to 18 months post-infection 1

2. Coagulation System Activation

   • COVID-19 induces a prothrombotic state through multiple mechanisms 1, 4:
     • Excessive inflammation
     • Endothelial cell activation and injury
     • Platelet activation
     • Hypercoagulability

3. Erythrocyte Damage

   • Complement deposition on circulating erythrocytes 1
   • Reduced deformability contributing to inflammation and hypoxia 1
   • Increased phospholipase A₂ activity affecting erythrocyte membrane integrity 1

4. Viral Persistence

   • Circulating SARS-CoV-2 spike antigen found in 60% of long COVID patients up to 12 months after diagnosis 1
   • Viral proteins/RNA detected in multiple tissues including cardiovascular system 1

Clinical Implications

1. Thrombotic Risk Assessment

   • High rates of venous, arterial, and microvascular thrombosis occur despite prophylaxis 1
   • Monitor D-dimer, fibrinogen, PT, and aPTT to assess thrombotic risk 1, 4
   • Consider prophylactic anticoagulation in COVID-19 patients 1

2. Diagnostic Value

   • NLR is a simple, low-cost predictor of COVID-19 severity, especially valuable in resource-limited settings 2
   • Complete blood count parameters can help predict clinical course and resource needs 4
   • Angiogenesis markers ANG1 and P-selectin have high sensitivity and specificity for predicting long COVID 1

3. Long-term Monitoring

   • Blood abnormalities can persist in long COVID 1
   • Ongoing thromboinflammation and hypercoagulable states may require extended monitoring 1
   • Multi-organ damage persists in a significant percentage of patients at one-year follow-up 1

Common Pitfalls in Interpretation

1. Misattributing All Abnormalities to COVID-19

   • Pre-existing conditions like hypertension, diabetes, and cardiovascular disease also cause endothelial dysfunction 5
   • Consider baseline status when interpreting changes

2. Relying Solely on Serology

   • Antibody tests cannot replace nucleic acid testing for active infection 1
   • Serology may yield false negatives in early disease or false positives due to cross-reactivity 1

3. Overlooking Microvascular Complications

   • Microclots and microvascular damage may not be detected by standard imaging 3
   • Consider specialized testing when symptoms suggest microvascular involvement

4. Ignoring Temporal Changes

   • Viral shedding patterns and inflammatory markers evolve throughout the disease course 1
   • Serial testing provides more valuable information than single measurements

By understanding these COVID-19-related blood alterations, clinicians can better predict disease severity, anticipate complications, and guide therapeutic interventions to improve patient outcomes.