Locum tenens coverage is a practical necessity for practices when a physician is out. But billing for locum services under the absent physician's NPI, using the Q6 modifier, has strict rules that many practices don't fully understand. Get this wrong and you're looking at repayment liability. Get this wrong at volume and the cost shows up fast, through denials, undercoding, or missed follow-up.
If you're working through these issues, our medical billing services can help you address them systematically.
The Q6 modifier tells Medicare that the service was provided by a substitute physician under the locum tenens arrangement. When you use Q6, you're billing as if the regular physician provided the service, meaning the claim goes out under the regular physician's NPI, at the regular physician's contracted rate.
This is legal and appropriate, but only under specific conditions. It's not a general-purpose "someone else covered my patients" modifier.
Medicare limits Q6 billing to 60 continuous days. If the regular physician is going to be out longer (extended medical leave, sabbatical, extended vacation) you have two options: the locum becomes credentialed under their own NPI and bills independently, or a different coverage arrangement is made.
The 60 days starts from the first day the locum sees patients and runs continuously. If the regular physician returns briefly and then leaves again, the clock doesn't reset. The 60 days is intended to cover genuine temporary absences, not extended coverage situations disguised as locum arrangements.
The substitute physician must be a physician, the Q6 modifier rules don't apply to NPs or PAs covering for a physician. If an NP is covering while a physician is out, those services bill under the NP's own NPI (at the NP's rate). Trying to bill an NP's services under the absent physician's NPI using Q6 is a billing error with compliance consequences.
Keep records of every Q6 arrangement: the dates covered, which physician was the substitute, which physician was the regular physician, and confirmation that the locum was paid fee-for-service or per-diem. CMS can ask for these records in an audit. If you can't produce them, the Q6 billing is presumptively improper.
Most commercial payers have their own policies on locum billing. Some allow billing under the regular physician's NPI in similar circumstances; others require the substitute to be credentialed with them and bill under their own NPI. Don't assume that because Medicare allows Q6, your commercial payers will too.
Review each commercial contract for locum tenens provisions. If the contract is silent and you bill a locum's services under the regular physician's NPI, you may be in breach of the contract's credentialing requirements. A call to the payer's provider relations line is worth the 20 minutes it takes.
Some practices use locum billing as a workaround when they've hired a new physician who isn't yet credentialed with payers. This is sometimes called "incident-to for physicians" or a panel buy-in arrangement, and it's a gray area. CMS hasn't explicitly prohibited billing new physician services under an established physician's NPI in all circumstances, but it's risky territory without careful legal review.
The better path: start the credentialing process the moment you know you're hiring a new physician. Credentialing typically takes 60–120 days, and many payers will backdating enrollment to the hire date if applied promptly. Plan ahead and you won't need a workaround.
Medicaid programs have their own locum tenens billing policies, which often differ from Medicare's. Some state Medicaid programs don't recognize the Q6 modifier at all and require that services be billed under the rendering provider's own NPI. Check your state Medicaid program's billing manual for the specific locum policy before assuming Medicare rules apply.
Q6 billing is only as strong as the records behind it. If a contractor asks, you need the dates covered, the names of the regular and substitute physicians, and confirmation that the locum was paid fee-for-service or per diem. Missing records make the Q6 claims unsupportable, and the repayment can include every claim submitted under the arrangement, not just the ones a reviewer sampled. Because contractors can extrapolate a sample error rate across the full lookback period, a documentation gap that looks minor on paper can become a much larger repayment demand.
The riskiest pattern is using locum billing as a workaround for a new physician who isn't yet enrolled. The article calls it a gray area, and payers treat a permanent hire billed as a temporary substitute as a misstatement of who provided the service. Contractors can review three years of claims, so if the arrangement was used repeatedly, plan for the whole history to be examined.
The best time to make sure a locum arrangement is compliant is before the locum's first patient. Confirm the regular physician's absence is temporary and the reason is one Medicare recognizes. Confirm the locum holds an active license, DEA registration if needed, and a valid NPI. Put a written agreement in place that states the dates, the compensation method, and the fact that the locum isn't an employee.
Then set up the billing side: who will submit, how the Q6 modifier will be applied, and where the records will be kept. A short form that captures each of those items, signed and dated, is the single best document to have if a question comes up.
Medicare limits Q6 arrangements to 60 continuous days, so a start date and an end date need to be on your calendar. If the regular physician's absence looks like it'll run longer, act early. The options are to end the arrangement, have the locum enroll on their own, or change the schedule. Waiting until day 59 leaves you with no good choices.
Log each day the locum worked and each patient seen. If the count of days and the claims don't line up, you'll want to know before a reviewer does.
Medicare limits Q6 billing to 60 continuous days, according to the article. If the regular physician will be out longer, the locum has to enroll and bill under their own NPI or the arrangement has to change.
No. The article says the substitute must be a physician and Q6 rules don't apply to NPs or PAs covering for a physician. Their services bill under their own NPI at their own rate.
Not necessarily. The article notes that most commercial payers have their own policies, and some require the substitute to be credentialed with them. Check each payer's policy before the locum starts.
The billing gaps most practices don't catch until they show up as denials. Get the checklist: free, no spam.
✓ Got it! Your info is saved: view the checklist now →
We don't share your info. Unsubscribe any time.
Revenue check: A quarterly sample of 20 to 30 claims here, checked against the supporting documentation, is cheap insurance against a $15,000 to $35,000 repayment surprise down the line.
Our team audits your RCM process end-to-end, no fluff, just the numbers that matter.
Request a Free Audit