When a substitute physician fills in for your practices’ doctors, you may be able to bill the services as locum tenens, also known as fee-for-time. The catch? Adding the correct modifier to your claim.

Check out a few important facts to ensure you apply the correct modifier to your locum tenens claims every time.

Look to Modifier Q6

If another physician is filling in for your practice’s doctor, you’ll need to append modifier Q6 (Service furnished by a locum tenens physician) to the fill-in physician’s CPT codes.

Example: A dermatologist at your office is out of the country for three weeks, and a locum tenens physician is taking their place during that period. The locum tenens doctor sees an established patient for a level-three office visit and documents the fact that the patient’s psoriasis is stable. The locum calls in a renewal for the patient’s medication.

In this case, the locum will report 99213-Q6 for the office visit. This represents a level-three established patient encounter performed by a locum tenens physician.

Submit the Claim With the Original Doctor’s NPI

The locum tenens provider isn’t a full-time employee of your practice, but is instead just filling in for the original doctor. Therefore, they won’t bill under their own NPI.

Instead, you should bill the locum’s services using the NPI of the doctor that the locum is filling in for. Keep in mind that there are certain payers that may ask you to include the locum’s NPI elsewhere on the claim for recordkeeping purposes, but the actual claim shouldn’t be billed under the locum’s NPI.

This underscores why modifier Q6 is so important. If the locum simply submitted the claim under the original doctor’s NPI without the Q6 modifier on it, the insurer would think the original doctor personally performed the service. If the records were ever audited and the payer saw that a locum performed it, they’d be likely to ask for the money back because the claim was submitted incorrectly.

Don’t Surpass the 60-Day Limitation

Medicare has a strict guideline for practices using modifier Q6 for locum tenens services: You can only do it for 60 continuous days. The sole exception is if your provider is on active military duty — in that case, you may be able to exceed the 60-day limit, but check with your payer first. In all other cases, don’t report locum tenens services for more than 60 days.