Denial codes · Denial code
CO-4 on a telehealth nutrition claim: fixing the modifier
By Javier Alvarez · Updated · 4 min read
| Official description | The procedure code is inconsistent with the modifier used. |
|---|---|
| Group code | CO (provider liable): do not bill the patient |
| Common remark codes | N822 (missing modifier), N823 (invalid modifier), N519 (invalid combination) |
| Telehealth POS | 02 other than home, 10 in the patient's home |
| Medicare professional claims | Identify telehealth with POS 02/10 (CMS MLN901705, Dec 2025) |
| Fix route | Corrected claim (frequency 7) with the payer's modifier and POS |
If most of your MNT visits are virtual, CO-4 is the denial you will meet most often after a payer changes its telehealth rules. It is a mismatch between the procedure code and its modifier, and on nutrition claims the modifier is almost always the telehealth one.
What CO-4 means
The X12 CARC list defines code 4 as:
"The procedure code is inconsistent with the modifier used."
It can mean the modifier is wrong, missing, or not allowed on that code by that payer. The remark code narrows it down. From the X12 remark code list:
- N822: "Missing procedure modifier(s)."
- N823: "Incomplete/Invalid procedure modifier(s)."
- N519: "Invalid combination of HCPCS modifiers."
The CO group code means the provider is liable. Do not bill the patient for a CO-4.
Telehealth modifier and POS combinations
There is no single right answer for 97802/97803 via telehealth. What each payer wants depends on its telehealth policy, and the policies change. These are the building blocks:
| Element | Meaning | Notes |
|---|---|---|
| POS 02 | "Telehealth Provided Other than in Patient's Home" | Patient at a clinic, workplace or other non-home site |
| POS 10 | "Telehealth Provided in Patient's Home" | Most virtual MNT visits |
| Modifier 95 | Synchronous telemedicine via real-time audio and video | Required by many commercial payers |
| Modifier GT | Via interactive audio and video telecommunication systems | Older; some payers still accept it, others reject it |
| Modifier 93 | Synchronous telemedicine via telephone or other real-time audio-only | Only where the payer covers audio-only |
Medicare
The current CMS telehealth booklet (MLN901705, December 2025) tells professionals to report telehealth with POS 02 or POS 10 as of January 1, 2024. In that booklet, modifier 95 is described for outpatient therapy services billed on institutional claims, and GT for institutional claims from critical access hospitals under method II. Some Medicare contractors publish their own modifier instructions for professional claims, so confirm with yours before changing a claim. MNT codes 97802, 97803 and G0270 are on Medicare's telehealth services list; where the patient can be (home or not) is a separate rule, covered in our Medicare telehealth for MNT guide.
Commercial and Medicaid plans
Many commercial payers want modifier 95 plus POS 02 or 10; some want POS 10 with no modifier; a few still require GT or ask for the in-person POS (11) plus 95. Medicaid programs and their managed care plans set their own rules by state. Keep a one-line entry per payer and update it when a CO-4 tells you something changed.
The usual causes on nutrition claims
- Wrong telehealth modifier for this payer: GT sent where the payer now requires 95, or 95 sent where the payer wants none.
- Modifier and POS disagree: 95 with POS 11 at a payer that expects POS 10, or POS 10 with no modifier at a payer that expects 95.
- Audio-only billed as video: a phone visit billed with 95, or billed with 93 at a payer that does not cover audio-only MNT.
- Modifier on a code the payer does not allow via telehealth: less common for 97802/97803, but check if you bill S9470 or group codes.
- Stale template: a practice-wide default modifier that no longer matches one payer's policy.
How to fix a CO-4
- Read the remark code and confirm which modifier the payer objected to.
- Look up the payer's current telehealth policy (provider manual or reimbursement policy) for 97802/97803: required modifier, allowed POS, and whether audio-only is covered.
- Check your note: was the visit real-time audio and video, and where was the patient? The note should say both.
- Send a corrected claim: frequency code 7 in Item 22 of the CMS-1500 (or the 837P frequency code) with the original claim number, the corrected modifier in 24D and the POS in 24B.
- Update your payer rules so the next claim goes out right.
If the payer returned CO-16 with M77 instead, the problem is the POS itself; see CO-16.
How to prevent CO-4
- Keep a telehealth table per payer: modifier, POS, audio-only yes/no, date last verified.
- Document modality and location in every note: "real-time audio and video; patient at home."
- Re-check policies each January, when many payers update telehealth rules.
- Audit your first telehealth claim with each new payer before sending the rest.
More on the full workflow in telehealth billing for dietitians and box-by-box claim help in CMS-1500 for dietitians. Every other code is in the denial code lookup.