Eligibility for AABD shall be determined for each applicant in accordance with the policies and procedures generally applicable in public assistance. The determination shall include appropriate verification of the factors of age, blindness or permanent and total disability in accordance with office regulations. A social services official shall make full utilization of Federal categorical assistance when granting aid to persons eligible or presumptively eligible for aid to the aged, blind or disabled. When there is a need and a presumption of eligibility for assistance under the combined AABD program, the pre-determination grant procedure shall be followed.