; or (2) by mailing the order by registered mail or certified mail or electronic equivalent addressed to the applicant at the last known address in the records of the Secretary. (e) Laboratories and blood and tissue establishments (1) Relation to laboratory certification pursuant to section 353 of the Public Health Service Act Nothing in this subchapter shall be construed to modify the authority of the Secretary with respect to laboratories or clinical laboratories under section 353 of the Public Health Service Act. (2) Avoiding duplication In implementing this subchapter, the Secretary shall avoid issuing or enforcing regulations or guidance that are duplicative of regulations or guidance under section 353 of the Public Health Service Act such that laboratories would be subject to conflicting regulatory obligations with respect to the same activity. (3) Blood and tissue Nothing in this subchapter shall be construed to modify the authority of the Secretary with respect to laboratories, establishments, or other facilities to the extent they are engaged in the propagation, manufacture, or preparation, including filling, labeling, packaging, and storage, of blood, blood components, human cells, tissues, or tissue products pursuant to any requirements under this Act or section 351 or 361 of the Public Health Service Act. (f) Not combination product (1) In general A product constituted of a device and an in vitro clinical test is not a combination product and may be regulated as a device or as a device and in vitro clinical test, notwithstanding section 201(ss)(3). (2) Guidance Not later than October 1, 2026, the Secretary shall issue final guidance, after an opportunity for public comment, addressing the considerations for regulating a product described in paragraph (1). Such guidance shall take into account the least burdensome requirements under subsection (c). (g) Practice of medicine Nothing in this subchapter shall be construed to limit or interfere with the authority of a health care practitioner to prescribe