All are true about Rinne's test except ?
Ans. is'd' i.e., Bone conduction is better in sensorineural hearing loss Rinne's Test The Rinne test is a tuning fork test that compares hearing by air conduction and bone conduction. The Rinne test is based on the idea that hearing mechanism is normally more efficient by air conduction (AC) than it is by bone conduction (BC), i.e., AC > BC in normal persons. For this reason, a tuning fork will sound louder and longer by air conduction than by bone conduction. However, this air conduction advantage is lost when there is a conductive hearing loss in which case the tuning fork sounds louder by bone conduction than by air-conduction. Method Administering the Rinne test involves asking the patient to indicate whether a vibrating tuning fork sounds louder when its base is held against mastoid process (bone conduction) or when its prongs are held near the pinna, facing the opening of ear canal (air conduction). After striking the fork, the clinician alternates it between these two positions so that the patient can make a judgement about which one is louder. Interpretation of Rinne's test The outcome of the Rinne test is traditionally called "positive" if the fork is louder by air conduction and this finding implies that the ear is normal or has sensorineural hearing loss. The results are called "negative" if the bone-conduction is louder than air-conduction, which is interpreted as revealing the presence of conductive deafness i.e., lesions of either external ear, tympanic membrane, middle ear or ear ossicles.. In conductive deafness Rinne's test will be negative if the conductive hearing loss is greater than 15-20 dB (minimum air bone gap 15-20 dB). That means, at least 15-20 dB of conductive hear loss is required to show bone conduction better than air conduction, i.e., Negative Rinne's test. A negative Rinne test for 256, 512 and 1024 Hz indicates a minimum air-bone gap (ABG) of 15, 30, 45 dB respectively. Therefore, AB gap can be made if tuning forks of 256, 512 and 1024 Hz are used : - A Rinne test equal or negative for 256 Hz but positive for 512 Hz indicates air-bone gap of 20-30 dB. A Rinne test negative for 256 and 512 Hz but positive for 1024 Hz indicates air-bone gap of 30-45 dB. A Rinne negative for all the three tuning forks of 256, 512, and 1024 Hz, indicates air-bone gap of 4560 dB. Rationale of positive test Positive test (AC > BC) is seen in :? 1. Normal person It has already been explained that air conduction is better than bone conduction, thus Rinne test is positive in normal person. 2. Sensori-neural hearing In sensorineural hearing loss, the defect is in cochlea or VIII nerve or its central connection. There is no defect in conductive apparatus of ear (air conduction) or in mastoid bone (bone conduction). As air conduction is better than bone conduction, Rinne test will be positive (because both air conductive apparatus and bone conductive apparatus are normal and the pathology is distal to them). Negative test (BC >AC) is seen in : ? 1. Conductive deafness As the conductive apparatus is defective, bone conduction becomes better than air conduction (BC > AC). 2. Severe unilateral sensorineural hearing loss Here the Rinne test is false negative (not true negative) as it is interpreted by the patient that BC > AC, but actually it is not. In reality this response is from the opposite ear because of transcranial transmission of sound during bone conduction testing. This can be prevented by masking the non-test ear with Barany's box while testing the bone conduction. Weber test will help for such situation.
Positive in normal ear
Positive in sensorineural hearing loss
Minimum 15-20 dB air bone gap is required in conductive deafness
Bone conduction is better in sensorineural hearing loss