Coordination of benefits. Which plan is primary?

I received a couple of ominous looking letters from Boston Children's hospital, letting me know that my claim has "been suspended" by my insurance carrier, Blue Cross Blue Shield of Massachusetts.Unlike a couple months ago, when Blue Cross accidentally cancelled my family's entire policy (oops!) while trying to remove an adult dependent at my request, this time it was due to a "coordination of benefits" issue.Here's the situation. Another dependent of mine is a college student in a different state. Our Blue Cross HMO doesn't work out of state, so we buy an additional insurance plan from the college. (Also one more policy for varsity athletic participation, but that's another story!)When this dependent had services at Boston Children's, we listed the Massachusetts plan as primary. But at least according to the BCBS MA rep I spoke with today, the out-of-state plan should be primary because my dependent is the subscriber, unlike on our family plan where they are listed as a dependent. So even though the out-of-state plan is likely to deny the Massachusetts claim as out-of-network, we need that denial first before submitting to BCBS MA. Make sense?Oh, and to make things a little more complex, the rep said I need to ask the other plan if they follow the "standard coordination of benefits rules." Apparently some student plans don't.What fun!—–By healthcare business consultant David E. Williams, president of Health Business Group