As per the data provided by the Bureau of Labor Statistics, there are more than 56,000 occupational therapy assistants (OTAs) working in the USA. And this number is growing very fast. In one way or another, the OTAs play an important role in all therapy practices and services. But as a biller, how will you identify if an OTA helped in the treatment of a patient?
The answer is by using the CO modifier.
We have created this guide to help you understand how to use this modifier correctly in your claims. We will start with the basics and explain what this modifier actually means, then move on to some use cases, and finally provide some essential guidelines that will help you use CO more accurately. So, let’s start.
CO Modifier – Description
The CO modifier is defined as:
“Outpatient occupational therapy services furnished in whole or in part by an occupational therapy assistant.”
The definition is self-explanatory. CO is used to bill the services of an occupational therapy assistant. However, the important phrase to explain in this definition is “furnished in whole or in part”. Most billing mistakes related to the CO modifier are made because billers don’t understand this part correctly.
Centers for Medicare & Medicaid Services (CMS) has a well-defined threshold through what it calls the de minimis standard. Once an OTA independently furnishes more than 10 percent of the total time for a given procedure or unit, it will qualify for the “in part” requirement, and you will have to append modifier CO to the claim line. If, in case the OTA provided assistance, but their services are below the threshold, the OTA’s contribution is neglected.
Another important point to note is that CO reduces the reimbursement amount by 15%. However, this reduction is per claim line and not for the entire claim.
Appropriate Use Cases for CO Modifier
Here are a couple of real-world scenarios in which the CO modifier can be used:
Scenario 1
Suppose a patient had a traumatic brain injury. He is recovering from it but needs occupational therapy as well to get back to his routine life and perform basic tasks like dressing and grooming. So, the patient visits the therapist for his scheduled visit. The occupational therapist spends 14 minutes with the patient on a cognitive intervention procedure. This accounts for 1 unit of the procedure.
After this, the OTA takes over for another type of therapy related to a different CPT code. The OTA works independently and spends 21 minutes with the patient. Using the 8-minute rule, 21 minutes means 1 unit. So, in this scenario, the billing department can bill one unit of the code that the OT performed, and on another claim line use one unit of the code that the OTA performed and append the CO modifier and GO to it.
Scenario 2
Let’s consider another scenario. Suppose a patient recovering from a rotator cuff repair comes in for a session of therapeutic activities. The occupational therapy assistant works with him for 10 minutes, guiding him through exercises to rebuild shoulder mobility. Later in the same visit, the supervising therapist steps in and independently works with the patient for another 5 minutes on the same activities.
Since the OTA’s 10 minutes make up well over 10 percent of the combined 15-minute unit, the billing team bills the claim line with modifier GO, and CO appended to it.
Accurate Usage Guidelines for CO Modifier
Here are some additional guidelines that will help you use the CO modifier correctly in your claims:
CO Applies Only to Certain Claim Types
You cannot use the CO modifier on all types of occupational therapy claims. There are some limitations to it. It applies to claims paid under the Physician Fee Schedule or under Section 1834(k) of the Social Security Act.
To put it simply, you can use it for claims of outpatient hospitals, rehabilitation agencies, skilled nursing facilities, home health agencies, and comprehensive outpatient rehabilitation facilities.
You cannot use CO for critical access hospitals, which are paid on a cost basis rather than the fee schedule. Also, CO is not applicable for rural health clinics or federally qualified health centers.
CO Must Be Paired With the GO Modifier
Another important point to note is that you cannot use CO alone on a claim. It must always be paired with the GO modifier.
A claim carrying the CO modifier without GO, or the reverse pairing of CQ with GO instead of GP, is rejected as unprocessable rather than simply denied.
Know the Exceptions that Override the De Minimis Standard
There is a scenario in which the 10% de minimis rule can be neglected. It is called the 8-minute rule exception.
On the final unit of a multi-unit day, if the OT alone provides 8 minutes or more of that unit, the line is billed without modifier CO, regardless of how many minutes the OTA also contributed.
Final Thoughts on CO Modifier
We have reached the end of this guide. So, let’s wrap up everything with a quick recap of the important points that we discussed.
- The CO modifier is used to bill the services of an occupational therapy assistant.
- For it to be valid, the OTA must spend at least 10% of the session with the patient.
- CO should always be paired with the modifier GO.
- The 8-minute exception can override the 10% de minimis rule.
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