A person employed by a school district in a position requiring certification qualifications who holds a valid special credential authorizing the teaching of lipreading or the teaching of the deaf and hard of hearing or a standard teaching credential with specialized preparation in the area of the deaf and hard of hearing or in the area of the speech and hearing handicapped or who holds a certificate of registration to serve as a school audiometrist issued by the State Department of Health Services may, subject to Section 49451, test the hearing of pupils of the district through the use of an audiometer for the purpose of detecting pupils with impaired hearing.