Is a lactic acid level necessary for diagnosing a pulmonary embolism (PE)?

Lactic Acid Testing is Not Recommended in the Diagnostic Workup of Pulmonary Embolism

Lactic acid testing is not recommended or required in the diagnostic workup of pulmonary embolism (PE) as it is not included in any evidence-based diagnostic algorithms for PE. 1

Evidence-Based Diagnostic Algorithm for PE

The diagnosis of PE should follow a structured approach based on clinical probability assessment, D-dimer testing, and appropriate imaging studies:

Step 1: Clinical Probability Assessment

• Use validated clinical prediction rules such as Wells score or Geneva score 1
• Categorize patients into low, intermediate, or high clinical probability of PE

Step 2: D-dimer Testing

• For patients with low or intermediate clinical probability:

  • Obtain D-dimer measurement using a highly sensitive assay 1
  • Consider age-adjusted D-dimer cutoffs (age × 10 ng/mL) for patients >50 years 1
  • If D-dimer is negative, PE can be safely excluded without further testing
  • If D-dimer is positive, proceed to imaging

• For patients with high clinical probability:

  • D-dimer testing is not recommended as a negative result does not safely exclude PE 1
  • Proceed directly to imaging

Step 3: Imaging

• CT pulmonary angiography (CTPA) is the first-line imaging test for suspected PE 1
• Ventilation-perfusion (V/Q) scanning is an alternative when CTPA is contraindicated or unavailable 1
• Lower limb compression ultrasonography may be useful in specific circumstances 1

Why Lactic Acid is Not Part of PE Diagnosis

The 2019 ESC Guidelines 1 and the 2015 ACP Best Practice Advice 1 make no mention of lactic acid measurement in their comprehensive diagnostic algorithms for PE. These guidelines focus on:

1. Clinical probability assessment
2. D-dimer testing
3. Imaging studies (primarily CTPA)

Lactic acid elevation is a non-specific finding that can occur in many conditions causing tissue hypoxia or hypoperfusion. While patients with massive PE causing hemodynamic compromise may develop lactic acidosis, this finding is neither sensitive nor specific for PE diagnosis.

Prognostic Assessment in PE

For risk stratification after PE diagnosis is confirmed, the guidelines recommend:

• Assessment of hemodynamic status (presence of shock or hypotension) 1
• Evaluation of right ventricular function (by echocardiography or CT) 1
• Cardiac biomarkers (troponin, BNP) 1

Notably, lactic acid is not included in these recommended prognostic assessments.

Common Pitfalls to Avoid

1. Overreliance on laboratory tests: Do not use lactic acid or other non-specific laboratory tests to rule in or rule out PE. Follow the evidence-based algorithm of clinical probability assessment, D-dimer testing, and appropriate imaging.

2. Skipping clinical probability assessment: Always begin with a structured assessment of clinical probability before ordering tests.

3. Inappropriate D-dimer testing: Do not order D-dimer in patients with high clinical probability of PE, as a negative result does not safely exclude PE in this population.

4. Premature imaging: Do not proceed directly to CTPA without appropriate pre-test probability assessment and D-dimer testing (in low/intermediate probability cases) to avoid unnecessary radiation exposure and contrast complications.

By following the evidence-based diagnostic algorithm outlined in current guidelines, clinicians can accurately diagnose or exclude PE while minimizing unnecessary testing, radiation exposure, and potential complications from contrast agents.