Reference values of diffusing capacity of non-smoking Chinese in Hong Kong.
OBJECTIVE
This study was conducted to define normal reference values and lower limits of normal (LLN) for single-breath carbon monoxide diffusing capacity (DLco) and DLco per unit of alveolar volume (Kco) for Chinese adults in Hong Kong.


METHODS
Healthy non-smoking men and women aged 18-80 years were recruited by random digit dialing. DLco and Kco were measured according to American Thoracic Society standards. Reference equations were obtained by multiple linear regression; LLN were derived by distribution-free method for estimation of age-related centiles.


RESULTS
Tests from 568 subjects (259 men, 309 women) were analysed. DLco declined with age in both genders, and increased with height and the interaction term of height and age in men and women, respectively. Considering Hb values did not improve the reference equations. Kco declined with age and increased with weight in both genders, while height and its interaction term with age were additional determinants in women. The reference DLco was lower than some Caucasian values, and was only explained partially by a smaller body size and alveolar volume in Chinese. The distribution-free method yielded better overall approximation to the fifth percentile compared with the traditional method of determining LLN.


CONCLUSIONS
The equations for reference values and LLN of diffusing capacity derived in this study are of clinical relevance to Chinese subjects.
Ip
Mary S M
MS
Department of Medicine, University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong, China. msmip@hkucc.hku.hk
Lam
Wai-Kei
WK
Lai
Agnes Y K
AY
Ko
Fanny W S
FW
Lau
Arthur C W
AC
Ling
Sai-On
SO
Chan
Johnny W M
JW
Chan-Yeung
Moira M W
MM
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People; D002681:China / Q000208:ethnology; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011653:Pulmonary Diffusing Capacity; D012016:Reference Values