Severity classification of diffusing capacity of the lungs for carbon monoxide (DLCO)^[1]

DLCO (preferred scale)*	Diffusion abnormality	DLCO (Z-score not available)
Z-score >1.645	Abnormally high	DLCO >140% predicted
Z-score –1.645 to 1.645	Normal	DLCO 76 to 140% predicted
Z-score –1.65 to –2.5	Mild impairment	DLCO 61 to 75% predicted
Z-score –2.5 to –4.0	Moderate impairment	DLCO 41 to 60% predicted
Z-score <–4.0	Severe impairment	DLCO <40% predicted

* The Z-score represents the normal distribution in healthy individuals taking into account reference equation parameters (eg, age, sex, height). A Z-score of 1.645 represents the upper limit of normal (95th percentile) and a Z-score of -1.645 represents the lower limit of normal (5th percentile). Z-score is recommended for severity grading to standardize measurement and reduce bias due to age, sex, and other factors. Some pulmonary function laboratories may still report using percent of predicted value; one grading scale for this measure is included.

Reference:

Stanojevic S, Kaminsky D, Miller M, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J 2022; 60:2101499.

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Severity classification of diffusing capacity of the lungs for carbon monoxide (DLCO)[1]

Severity classification of diffusing capacity of the lungs for carbon monoxide (DLCO)^[1]