CARC CO-151: Frequency/Units Exceeded — DME Supply Appeal Guide

CO-151 means the payer determined that the number of services or units billed exceeds what their policy allows — either per year, per episode, or per benefit period. Official description: "Payment adjusted because the payer deems the information submitted does not support this many/frequency of services."

This hits DME suppliers constantly because supplies like CPAP masks, filters, tubing, and oxygen accessories all have strict Medicare frequency limits codified in LCDs.

• Billing CPAP supplies before the allowed interval. Medicare's CPAP supply frequency limits are precise: cushions/pillows (A7031) = 2/month max; full mask (A7030) = 1 per 3 months; tubing (A4604) = 1 per 3 months; filters (A7037) = 2/month. Bill one day early and CO-151 fires automatically.
• Same or similar item already billed. If the patient received the same item from another supplier within the coverage window, the payer's same-or-similar check returns a hit and CO-151 fires.
• Exceeding oxygen supply limits. Oxygen contents and accessories have payer-specific limits tied to the equipment rental period and flow rate documentation.
• Missing CMN questions. The CMN for DME supplies must have all qualifying questions answered. If question 4 (estimated length of need) or question 5 (frequency) fields are blank or don't support the billed frequency, CO-151 applies.

1. Check the LCD for your HCPCS code. Medicare publishes exact frequency limits by HCPCS. Confirm the claim falls within the allowed window from the last paid claim date (not the last delivery date).
2. Run a same-or-similar check. Before billing replacements, check the Noridian Medicare Portal or call the IVR to confirm the patient hasn't received the same item from another supplier.
3. Review the CMN. If CMN questions don't support the billed frequency, get a corrected CMN from the ordering physician before resubmitting.
4. Adjust the date span if needed. If you billed the wrong service dates, a self-service reopening through the Noridian portal can correct the span without a full appeal.
5. Appeal with documentation if the frequency denial is incorrect — include the LCD, delivery logs, CMN, and clinical notes showing the patient's ongoing need.