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# 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 mucosa secreting glands and the thickness between the epithelium and cartilage that covers the bronchi. It isn't 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].

$\ RI = \frac {gland}{wall}$

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 mucous producing gland at the location of inspection.

A normal Reid Index should be smaller than 0.4, the thickness of the wall always more than double the thickness of the glands it contains. Hyperplasia and hypertrophy of mucous glands as in chronic bronchitis[2] causes them to be present at deeper levels in the bronchial wall and thicker in size, thus increasing the Reid Index beyond the normal value.

## References

1. ^ 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. [1]
2. ^ School of Medicine, Toulane University. [2]