In order to qualify for assistance to the disabled, an individual shall, in addition to the requirements set forth in section 68-1002, be considered to be disabled if he or she is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or which has lasted or can be expected to last for a continuous period of not less than one hundred eighty days or, in the case of a child under eighteen years of age, if he or she suffers from any medically determinable physical or mental impairment of comparable severity. In determining eligibility for assistance to the disabled, the Department of Health and Human Services may adopt the determination of the Social Security Administration that an individual is or is not disabled for the purposes of the federal programs of Supplemental Security Income or Old Age Survivors' and Disability Insurance, except that if the Social Security Administration has denied benefits to an individual on the basis of the duration of the individual's disability, the department shall perform an independent medical review of such individual's disability.