NEW YORK (MONEY Magazine) - Q. My husband is over 65 but continues to work full time. We get our primary health insurance from his employer and use Medicare Part A for secondary coverage.

He recently became sick and needs extensive care -- just as he's preparing to retire. Problem is, Social Security tells me we can't get Medicare Part B or Medigap set up until his group coverage ends, but I fear if we terminate group coverage while he's sick, we won't be covered in the interim, when we need it most.

Andrea Garis Bangor, PA.

A. Given the propensity of health-care bureaucracies to screw up even the simplest paperwork, you were smart to get ahead of this potential red-tape nightmare.

To help you strategize, we tapped Lori Donnelly Elm, a medical-claims expert in nearby Bethlehem, Pa.

Elm confirms that the shift from working to retired can be treacherous: "Never assume you're fully covered. If Medicare doesn't know they've become the primary health insurance, you can end up with stacks of bills and claims denials."

Part of your problem is that you were given incomplete information when you tried to enroll in Medicare Part B.

(For the record: Part A typically pays for inpatient hospital coverage, and Part B typically pays for outpatient health care and doctor visits. Most retirees need both and simply purchase Part B when they turn 65, at which point they are automatically enrolled in Part A.)

Waiting too long to enroll in Part B after 65 can also create problems.

If more than eight months have elapsed from the time of retirement or the time your employer coverage lapses (whichever is earlier), you'll pay a 10 percent higher premium for life -- and you may have to wait for the next calendar year to sign up, which can lead to serious coverage gaps.

Finally, you cannot buy supplemental (a.k.a. Medigap) insurance unless you already have Part B. More gaps, more worries.

Elm recommended something called special enrollment, which is designed to allow folks who've delayed retirement to pick up Part B immediately after they stop working, and without penalty.

No one told you about it, for some reason. But to pull it off, it took a village worth of help and documentation.

Elm needed a letter from your husband's employer stating his exact date of retirement (which is also when his group coverage would end).

She sent a copy to your insurer, Capital Blue Cross of Pennsylvania, so it would make note of the termination date. Capital is also your Medigap provider, and so you set up coverage that would begin on the first day of your husband's retirement.

Elm sent copies of all of this to Medicare, arranging for your enrollment in Part B to begin on that magical, overdocumented date. Nothing says insurance like a paper trail, eh?

When we last spoke, your husband's health troubles were behind him -- and he was enjoying a well-earned hunting trip.

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