In children with asthma, a breath test can measure the effects of exposure to urban air pollution, according to a new study.

The test measures levels of a compound called malondialdehyde in exhaled breath. The researchers found that malondialdehyde levels are related to both pollutant exposure and to nasal secretion of inflammatory compounds.

The team, led by Dr. Isabelle Romieu of the Instituto Nacional de Salud Publica, Cuernavaca in Mexico, recruited 107 children with asthma who lived in two areas of Mexico City with high population and traffic densities. A total of 480 random breath samples (four to eight per child) were collected over a 10-month period.

Measurements of air pollutants were obtained from government air-monitoring stations in the areas where the subjects lived.

Malondialdehyde concentrations in the breath samples correlated with levels of traffic-related pollutants, particularly ozone, the investigators report in the Journal of Allergy and Clinical Immunology.

Furthermore, the elevated malondialdehyde levels were associated with decreased lung function and with increased levels in nasal secretions of a naturally occurring substance, interleukin 8, that causes inflammation.

The researchers conclude that the level of malondialdehyde in exhaled breath is a suitable way of measuring the effect of traffic-related pollutants in children with asthma.

SOURCE: Journal of Allergy and Clinical Immunology, April 2008.