• Two groups of 33 subjects each, one experimental and one control, matched one-to-one for age and occupation, were chosen from a large number of subjects who were covered by special insurance for annual medical control at our hospital. The periodical checkups included cardiovascular, nervous, and renal systems, as well as vision and hearing. In addition routine blood tests, including whole blood viscosity, were also performed. The experimental group consisted of subjects in whom a bilateral, slight, and unexplained sensorineural loss of hearing was detected in the routine audiological testing, without any known reason. In the control group, the routine hearing tests demonstrated normal hearing. The differences between the two groups were statistically significant in pure-tone threshold level and in speech discrimination score, when the test was performed at a −5-dB signal-to-noise ratio. The results of the vestibular tests were normal in both groups. Hematocrit and whole blood viscosity were slightly but significantly higher in the experimental group if compared with the control group. The number of subjects with abnormal whole blood viscosity results was higher in the experimental group. The whole blood viscosity as the etiological factor responsible for the hearing deterioration is described.
(Arch Otolaryngol Head Neck Surg. 1990;116:820-823)