Yes, mainly units in contact with the ground: garden-level and first-floor units and those over a crawl space or basement. Upper floors usually read lower. The Ohio Department of Health recommends retesting multifamily buildings every five years.
More detail
Central Ohio has plenty of ground-contact rental stock: garden units in older buildings near Ohio State, walk-ups in the Short North and Italian Village, and slab-on-grade townhomes across the suburbs. Ohio's measurement protocol treats multifamily buildings separately from houses, and testers must file their own procedures for them with ODH, while a single condominium unit is measured like a home. Large buildings are mitigated under a different national standard, ANSI/AARST SGM-MFLB-2023, rather than the single-family one. A tenant can test a unit with a kit, but mitigation involves the building, so it belongs to the owner or the association. See landlords and radon and our commercial and multifamily service.