Evaluation of the Reid index in infants and cases of SIDS

The Reid index is an instrument for the evaluation of chronic bronchitis. The thickness of the mucosa and of its gland layer are measured and the relationship is expressed as a gland/wall ratio. Specimens were obtained from 124 autopsies from the German National Study on SIDS (GeSID). The cases were divided into three groups: group 1 typical SIDS ( n=47), group 2 SIDS with signs of mild inflammation of the respiratory tract ( n=50) and group 3 unnatural death controls ( n=23). The Reid index was measured in sections from the trachea, bifurcation/main bronchi and bronchioli (staining HE and PAS). The Reid index was remarkably constant throughout the different levels of the respiratory tract (standard deviation range 0.06-0.10). A comparison of the three groups did not show statistically significant differences. Group 1: mean Reid index trachea 0.37, bifurcation/main bronchi 0.38, bronchioli 0.39. Group 2: mean Reid index trachea 0.40, bifurcation/main bronchi 0.38, bronchioli 0.38. Group 3: mean Reid index trachea 0.39, bifurcation/main bronchi 0.38, bronchioli 0.41. It can be concluded that the dimensions of bronchial glands do not vary in cases of SIDS as compared to controls. This demonstrates that the Reid index has no significance in the vast majority of SIDS cases and that acute inflammation commonly does not produce an elevated Reid index. In addition, the Reid index was confirmed to be a valid instrument to study the respiratory tract including the trachea due to its stability and it was found that the Reid index is age-dependent: compared to adults, the ratios in infants were higher.