Medicare Just Reminded Practices It Denies Duplicate Lab Tests. Modifier 91 Is Not the Workaround.

In its MLN Connects newsletter of October 1, 2026, CMS ran a short item under the heading "Laboratory Testing: Medicare Denies Duplicate Tests." The message is plain: Medicare does not pay for duplicate tests unless they are medically necessary. CMS gave one example. Medicare won't pay for a second vitamin D test unless it is medically necessary.

The item points to three places: the Medicare Claims Processing Manual, Chapter 16; a billing and coding article on repeat or duplicate services on the same day; and the CY 2027 Physician Fee Schedule proposed rule, which included a request for information on duplicate laboratory testing, imaging, and result sharing and interoperability. CMS says it is exploring options to address these issues in future rules. A reminder like this usually means the topic is on CMS's list, so it's a good week to look at your own lab claims.

What Medicare counts as a duplicate

Chapter 16 sets out the rules the newsletter cites:

• Section 90.3 tells Medicare Administrative Contractors to deny duplicate services found in the same processing cycle or in claim history. A claim line is treated as a duplicate when it matches on the same provider, the same beneficiary and the same date of service.
• Section 90.5 says a physician may order a mix of panels and individual tests, but should review what tests are in each panel and not order individual tests that might duplicate tests in the panel. The manual's next sentence is short: Medicare denies duplicate tests.
• Section 90.2 says that for dates of service on or after January 1, 2019, laboratories bill the panel code, not the individual components, when every component of the panel is performed. Claims are returned as unprocessable if the panel code is not billed.

So a duplicate isn't only the same code twice. It can be a component test ordered next to a panel that already contains it, on the same patient and the same day.

Where modifier 91 fits, and where it does not

Section 100.5.1 of Chapter 16 explains the modifier. Modifier 91 shows that a lab test paid under the Clinical Laboratory Fee Schedule was performed more than once on the same day for the same patient, when it was necessary to obtain multiple results in the course of treatment.

The same section lists when it may not be used:

• when a test is rerun to confirm the first result;
• when a test is repeated because of a problem with the specimen or the equipment;
• for any other reason when a normal, one-time, reportable result is all that is required;
• when a standard HCPCS code already describes the series of results, such as glucose tolerance tests or evocative and suppression testing.

The manual also says improper use of these modifiers is likely to indicate a fraudulent or abusive circumstance, and that contractors should refer evidence of excessive use to their program integrity unit. Adding modifier 91 to get a duplicate past an edit turns a denial into an audit risk.

Where duplicates usually start

Duplicate lab charges are rarely one person's mistake. They usually come from how orders and charges are set up. Places worth checking:

• Order sets or favorites that include a panel and, separately, a test that is already one of its components.
• Two clinicians ordering the same test for the same patient on the same day, for example at a visit and again at a follow-up.
• A test run in the office lab and also sent to a reference lab.
• A test reordered because the earlier result wasn't in the chart, which is the problem CMS's result-sharing question is about.

A short check for practices that order or bill labs

A focused review covers most of the risk:

• Pull lab denials for the last 90 days and sort them by patient, date of service and code. Look for duplicate-service denials and for component tests billed next to a panel.
• Compare each order set against the panels it contains, and remove individual tests that are already inside a panel ordered on the same set.
• If your practice bills its own lab work, bill the panel code when every component is performed, as section 90.2 requires.
• Use modifier 91 only when a repeat test on the same day was needed for multiple results in the course of treatment, and make sure the record shows the reason and the time of each test.
• Do not bill reruns for quality control, specimen problems or result confirmation as separate tests.
• Before reordering a test such as vitamin D, check whether a recent result already exists, and document why a repeat is needed when it is.
• Commercial and Medicaid plans set their own duplicate and frequency rules. Confirm each major payer's policy before changing their claims.

None of this decides whether a particular test is covered. Coverage, documentation and payer policy still apply.

Make lab claims part of the routine review

Duplicate lab denials are small one at a time, which is why they often go unworked. VOSKPO helps practices sort lab denials by cause, fix the order or charge setup behind them, and keep a human review on modifier use before claims go out. A revenue review can show where duplicate denials touch a practice's own claims.