Bipartisan HSA Improvement Act of 2018 This bill amends the Internal Revenue Code to modify rules for health savings accounts (HSAs) regarding eligibility and interactions with other tax-favored health accounts. The bill specifies that receiving or being eligible to receive certain employment-related items and services at an employer-sponsored (e.g., an on-site clinic) or retail health care facility is not considered health care coverage that disqualifies an individual from participating in an HSA. The items and services include physical examinations, immunizations, drugs other than a prescribed drug, treatment for injuries occurring in the course of employment, drug testing as a condition of employment, hearing or vision screenings, and other similar items and services that do not provide significant benefits in the nature of medical care. The bill also (1) allows an eligible individual to make HSA contributions if a spouse has a flexible spending arrangement (FSA) as long as the FSA does not also reimburse the expenses of the spouse with the HSA, and (2) modifies the rules for using FSA or a health reimbursement arrangement terminations or conversions to establish an HSA.