If you have insurance through your employer, you probably are in a managed care plan. If you are in Medicare, you might be in a managed care plan too. You can't always tell from the name of the plan. It's the rules that count.

When you signed up for your insurance plan, you agreed to its rules. You were probably given a packet that describes the kind of coverage you have. To avoid misunderstandings about your coverage, you need to read the rules of your insurance plan. For most plans, the important rules fall into these groups:

• Doctors and hospitals the plan works with. Managed care plans sign contracts with certain doctors and hospitals to care for their plan members. Your plan may refer to them as providers. This group of providers is often called the plan's network. Like you, they have agreed to follow the plan's rules. Your insurance company may not pay for you to go to a provider who is not in its network. If it does pay for you to use a provider outside your network, it may pay less than it would for a network provider. In either case, you are responsible for the part of the bill that the plan doesn't pay.

Even if your doctor is part of the plan's network, he or she may prefer to send patients to a hospital that isn't in the network. If so, ask if your doctor can send you to a hospital in the network. If that isn't possible, you can ask the insurance company if it will approve the use of the out-of-network hospital. If no other arrangements can be made, you might have to see another doctor.

• Rules for seeing specialists. Many managed care plans won't pay for you to see a specialist unless your primary care physician (usually your family doctor) thinks it is necessary. If you see a specialist without a referral, you might have to pay more for the care you receive.

• Rules for getting expensive services. If your doctor decides that you need to go to the hospital, have surgery, or have certain tests, your insurance company may refuse to pay for it unless it can preauthorize the treatment (approve it beforehand).

• Medicines the plan approves. Almost every managed care plan has a drug formulary. A formulary is a list of prescription medicines that your health plan has approved. If a drug isn't on the formulary, you'll probably have to pay more for it. Your insurance company can give you a list of drugs that are on the formulary. If necessary, show the list to your doctor when the doctor writes you a prescription.

Working with your managed care plan can be confusing, but remember: You can always call your insurance company for help. Write down its phone number where you won't forget it!