# Reid index

The **Reid Index** is a mathematical relationship that exists in a human bronchus section observed under the microscope. It is defined as ratio between the thickness of the submucosal mucus secreting glands and the thickness between the epithelium and cartilage that covers the bronchi. The Reid index is not of diagnostic use *in vivo* since it requires a dissection of the airway tube, but it has value in *post mortem* evaluations and for research.[1]

## Calculation

where:

**RI**is the Reid Index*wall*is the thickness of the airway wall between the epithelium and the cartilage's perichondrium*gland*is the thickness of the mucus-producing gland at the location of inspection.

## Interpretation

A normal Reid Index should be smaller than 0.4, the thickness of the wall is always more than double the thickness of the glands it contains. Chronic smoking causes submucosal gland hypertrophy and hyperplasia, leading to a Reid Index of >0.5 indicating chronic bronchitis.[2]

## References

- B. Karger, T. Fracasso, B. Brinkmann and T. Bajanowski.
*Evaluation of the Reid index in infants and cases of SIDS*. International Journal of Legal Medicine. Volume 118, Number 4 / August, 2004. - School of Medicine, Tulane University

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