A referral is like getting a prescription from your regular doctor to go see a specialist. Referrals have expiration dates. Some have a limit on the number of visits. So, if you need to see the specialist after the end date on the referral or for more visits, you will need to get another referral.
You could pay a lot more
If your plan requires a referral but you don't get one, you could pay a lot more. For example, your plan may charge you a penalty, cover the visit at a lower level, or not cover it at all.
Check your summary of benefits and coverage document or call customer service to find out when you need a referral. While you're at it, ask your plan when you need to get preauthorization as it's possible to also need preauthorization even though you have a referral. Learn more.
You don't always need to get a referral
Check with your plan. Sometimes there are certain specialists that you can see without a referral. Some plans don't require referrals at all as long as you see an in-network doctor.