What does an elevated DLCO/VA of 117% predicted indicate and how is it managed?

Elevated DLCO/VA of 117% Predicted

An elevated DLCO/VA of 117% predicted is generally a benign finding that does not require specific management, but warrants clinical correlation to exclude pulmonary hemorrhage, left-to-right cardiac shunts, polycythemia, or early pulmonary vascular disease.

Understanding the Measurement

The DLCO/VA ratio (also called KCO or transfer coefficient) represents diffusing capacity corrected for alveolar volume 1. When this ratio is elevated above predicted values, it indicates that gas transfer per unit of ventilated lung volume is increased 2.

Key physiologic considerations:

• DLCO/VA primarily reflects the membrane diffusing capacity (Dm) component and capillary blood volume (Vc) relative to the ventilated alveolar space 2
• An elevated ratio can occur when DLCO is preserved or increased while VA is reduced, or when DLCO is disproportionately elevated relative to VA 3
• The measurement should be performed according to ATS/ERS standards with quality grading to ensure accuracy 1

Clinical Significance of Elevation

Elevated DLCO/VA (>110% predicted) has distinct clinical implications:

• Pulmonary hemorrhage: Increased hemoglobin in alveoli binds CO avidly, raising DLCO and DLCO/VA 2
• Polycythemia: Elevated hemoglobin concentration increases red cell volume (Vc), raising both DLCO and DLCO/VA 1
• Left-to-right cardiac shunts: Increased pulmonary blood flow elevates capillary blood volume 2
• Obesity (mild elevation): Class I obesity can increase DLCO/VA by 5-7.5% per 5 kg/m² BMI increase, though this typically produces values in the 105-110% range rather than 117% 3
• Early pulmonary vascular disease: Paradoxically, a raised DLCO/VA ratio (≥110% predicted) combined with low absolute DLCO (<67% predicted) predicts pulmonary vascular disease 2

Diagnostic Approach

When encountering DLCO/VA of 117% predicted, systematically evaluate:

1. Review the absolute DLCO value - If DLCO is also elevated (>120% predicted), consider pulmonary hemorrhage, polycythemia, or left-to-right shunt 2

2. Check hemoglobin concentration - DLCO measurements should be corrected for hemoglobin; polycythemia (Hgb >16 g/dL in women, >18 g/dL in men) can elevate both parameters 1, 3

3. Assess for reduced VA - If VA is <80% predicted while DLCO/VA is elevated, this suggests incomplete lung expansion during the maneuver or true restrictive physiology 1, 3

4. Evaluate quality of the test - Ensure the maneuver met Grade A or B criteria: VI/VC >85-90%, breathhold time 8-12 seconds, sample collection <4 seconds 1

5. Look for clinical signs of:

   • Recent hemoptysis or pulmonary hemorrhage
   • Symptoms of polycythemia (headache, pruritus, erythema)
   • Cardiac murmur suggesting shunt
   • Obesity (BMI ≥30 kg/m²) 4, 3

Management Recommendations

For isolated elevation of DLCO/VA to 117% predicted with normal absolute DLCO:

• No specific intervention is required - This represents a normal variant or technical factor 3, 5
• Document BMI, as obesity can account for 5-7.5% elevation per 5 kg/m² increase 3
• Ensure hemoglobin correction was applied to the DLCO measurement 1

If absolute DLCO is also elevated (>120% predicted):

• Obtain complete blood count to assess for polycythemia 3
• Consider chest imaging if pulmonary hemorrhage is suspected clinically
• Perform cardiac evaluation if left-to-right shunt is suspected based on examination

Critical pitfall to avoid:

• Do not assume elevated DLCO/VA always indicates health - when combined with reduced absolute DLCO (<67% predicted), an elevated DLCO/VA ratio (≥110%) predicts pulmonary vascular disease and warrants further evaluation with echocardiography and possibly right heart catheterization 2

Reference Equation Considerations

The specific reference equations used affect interpretation:

• Global Lung Function Initiative (GLI) reference values show the smallest effect from BMI and obesity compared to older equations 3
• European Coal and Steel Community (ECSC) references may produce sex-dependent differences in DLCO/VA interpretation 5
• Older reference equations (pre-2005 ATS/ERS standards) may underestimate predicted values, making normal measurements appear elevated 5

Verify which reference set was used - if outdated Finnish (Viljanen 1982) or similar pre-2005 references were applied, the apparent elevation may be artifactual, as these produce mean predicted DLCO/VA of 102-103% in healthy individuals 5