A Medicare Screening Done a Week Early Is Denied. Without an ABN, Your Practice Absorbs It.

October is when practices push screenings. In its MLN Connects newsletters of October 15 and October 22, 2026, CMS asked practices to talk to Medicare patients about prostate cancer screening and breast cancer screening, and to find out when each patient is next eligible. That last step is where a well-meant reminder can turn into a denied claim.

Here is a hypothetical case. A patient had her last screening mammogram on November 20, 2025. On October 27, 2026, she calls to book this year's, and the scheduler, seeing that almost a year has passed, gives her the first open slot on October 29. Counted in days, that is eleven months and nine days. Medicare does not count in days. Under its rule she becomes eligible on November 1, 2026, so a screening on October 29 is too early and the claim is denied.

How Medicare counts the interval

For screening mammography, 42 CFR 410.34 allows payment for a woman over 39 only "after at least 11 months have passed following the month in which the last screening mammography was performed." The count starts with the month after the last test. For a test in November 2025, the eleven months are December through October, so the patient is eligible from the first day of November 2026, whatever the day of the month the last test was done.

The screening prostate-specific antigen (PSA) test and the screening digital rectal exam follow the same wording in 42 CFR 410.39: a man over 50 qualifies only if he has not had one paid by Medicare during the 11 months following the month of the last one. The month rule works in both directions. A man whose last screening PSA was on March 3, 2026 is eligible from March 1, 2027, two days before the anniversary.

Screening Pap tests and pelvic exams use a longer clock. CMS's booklet on them gives every 24 months (at least 23 months after the most recent one) for most patients, every year (at least 11 months after) for patients who meet the high-risk or childbearing-age conditions, and HPV screening once every five years (at least 59 months). The booklet lists screening before the patient is eligible as a reason for denial.

Who pays when it is too early

A screening that meets Medicare's conditions costs the patient nothing: no deductible and no coinsurance. A screening that is too early is not a covered screening at all. Somebody still has to pay for it, and the answer depends on one piece of paper.

Medicare's claims manual (Chapter 30, section 40.2.2) makes frequency limits one of the few cases where an Advance Beneficiary Notice (ABN) may be given routinely, as long as it names the frequency limit as the reason Medicare is expected to deny. With a valid, signed ABN, the claim line carries the GA modifier and the patient can be billed if Medicare denies. Without one, section 50.9 says the provider is likely liable when it knew or should have known Medicare would not pay. The practice cannot collect from the patient and must refund anything it already took.

The denial lands on whoever bills the service: your practice for the screenings it performs, and the imaging center or lab for the tests it orders from them. Either way, a screening booked a few days early becomes a write-off for someone, or, if a statement goes out anyway, a refund owed to an upset patient who was told the test was free.

Why the eligibility check alone can mislead

Medicare's eligibility system returns a next eligible date for many preventive services, and CMS explains it plainly: a future date means you cannot provide the service until that date, and a past date means the patient is eligible now. The same fact sheet adds the limit that matters: those dates are calculated from claims Medicare has paid under Original Medicare.

A screening done somewhere else last month, with a claim that has not been paid yet, will not show. Neither will a test the patient had while enrolled in a Medicare Advantage plan. The next eligible date is a good starting point, but it should be confirmed against the patient's own history: your records, outside results and what the patient tells you.

A front-desk check for screening season

This is general information, not legal or clinical advice. A practice can start with these steps:

• Before booking or ordering a screening, look up the next eligible date in HETS, your MAC's portal or your clearinghouse, and write it in the appointment note.
• Count the interval the way Medicare does: start with the month after the last test, and book on or after the first day of the month that follows the required number of months.
• Ask the patient whether they had the same screening anywhere else in the last two years, including under a Medicare Advantage plan, and record the answer.
• If the patient wants the screening before the eligible date, give an ABN that states the frequency limit as the reason, get it signed before the service and add the GA modifier to that line only.
• When a frequency-limited screening is billed together with other services, make sure the ABN names the screening itself. CMS says an ABN for one frequency limit does not shift liability for other items on the same claim.
• Each month, pull your frequency denials by service and by staff member who scheduled them. The same few causes tend to repeat.

Count the months before you book

CMS wants more patients screened, and so do most practices. The money is lost in the space between a reminder and a rule that counts months, not days. A few minutes at scheduling, a date in the appointment note and an ABN when the patient chooses to go early protect both the patient and the practice. If you want to see how many of your recent preventive denials were frequency denials, and whether an ABN was on file for each, a revenue review can look at that for one payer and one quarter.