Copayment: a one-time amount that you pay for a specific medical service or supply. It may be a fixed dollar amount or a percentage of the charge. The insurance pays the rest of the charge.
For example, you pay $25 for a physician office visit, or $40 for a brand name prescription, or 20% of a lab test charge.
Deductible: an amount that you have to pay each year before the insurance starts to pay. It may apply to all covered expenses or only to a certain category of expenses, e.g., there is a copay for physician office visits and prescriptions, so there is no deductible for those expenses but the deductible applies for everything else.
There is usually a deductible in PPO and Indemnity plans. Some HMO plans have no deductible and have only copays.
Coinsurance: is always expressed as a percentage. There is the percentage you pay and the percentage that the insurance pays. It may be annual or it may be per incident.
Coinsurance is most common after a deductible and ususally has a limit, e.g., You pay a $1,000 deductible, then you pay 20% of the next $5,000, and then the insurance pays the balance of covered expenses for that benefit year. So your maximum out-of-pocket for covered expenses in any year is $2,000 ($1,000 deductible plus $1,000 coinsurance).
Stop-loss: that is the $5,000 in the Coinsurance example. It is the amount of covered expenses at which you stop paying coinsurance.
Precertification: Required for expensive procedures in most plans where independent medical providers are used, which is most plans. The insurer must be notified in advance that the procedure is scheduled. For emergencies, notification must be made promptly after the event.
For scheduled procedures, the insurer can affirm that the procedure is a covered expense and has the opportunity to determine that it is appropriate. If the procedure can not be justified as accepted medical practice, the insurer can give advance notice that it will refuse payment.
Utilization Review: Required in most plans. The insurer monitors ongoing treatment in certain categories, i.e., those likely to be expensive, to determine that it is appropriate and cost-effective. If the insurer allows its premium income to be wasted on unnecessary or ineffective care, it will be reflected in higher premiums.