Glycerol test is done in

Glycerol is a dehydrating agent. When given orally, it reduces endolymph pressure and thus causes an improvement in hearing. It is diagnostic of Meniere's disease. The patient is given glycerol(1.5ml/kg) with an equal amount of water and a little flavouring agent or lemon juice. Audiogram and speech discrimination scores are recorded before and 1-2 hr after ingestion of glycerol. An improvement of 10db in two or more adjacent octaves or gain of 10 c/o in discrimination score makes the test positive. There is also improvement in tinnitus and in the sense of fullness in the ear. The test has a diagnostic and prognostic value. These days, the glycerol test is combined with electrocochleography. Ref: Diseases of EAR, NOSE and THROAT by PL Dhingra 7th Edition page no.113