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diffusion capacity of carbon monoxide (DLCO)
Principle:
- used in the assessment of pulmonary function, alveolar integrity.
- dependent upon the thickness of the alveolo-capillary membrane, the hemoglobin level & the pulmonary capillary volume
Clinical significance:
- measures ability of the lungs to transfer gas (CO2 & O2) across the alveolar-capillary membrane [2]
Increases:
1) asthma (some) (FEV1/FVC < 0.7)
2) pulmonary hemorrhage
3) early CHF
4) supine position
5) after exercise
6) polycythemia
7) obesity
8) left to right shunt
Decreases:
1) COPD. emphysema, bronchiectais (FEV1/FVC < 0.7)
2) restrictive lung disease
3) diffuse parenchymal lung disease (reduced lung volumes) [2]
4) pulmonary vascular disease, anemia (normal lung volumes) [2]
- isolated decrease in DLCO with otherwise normal PFTs
- anemia - 1 g/dL decrease in hemoglobin decreases DLCO by 7%
- pulmonary hypertension
- recurrent pulmonary emboli
5) pneumonectomy
Interpretation:
DLCO (% predicted) Assessment
> 140% increased
80-140% normal
60-80% mildly reduced
40-60% moderately reduced
< 40% severely reduced
- low lung volumes & normal DLCO suggests extrapulmonary etiology (obesity) [2]
General
pulmonary function test (PFT)
diffusion
References
- Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed)
Lippincott-Raven, Philadelphia, 1998, pg 735
- Medical Knowledge Self Assessment Program (MKSAP) 11, 16.
American College of Physicians, Philadelphia 1998, 2012
- Medical Knowledge Self Assessment Program (MKSAP) 19
Board Basics. An Enhancement to MKSAP19.
American College of Physicians, Philadelphia 2022