COLUMBIA, S.C. – You can check my math on this one, but I think CMS miscalculated the rental rates for CGMs and insulin pumps in the recent proposed rule CMS-1828-P. The error is related to the cumulative supply allowances embedded in the reimbursement rate, and it adds up over the five-year useful life of the related devices.
30 Days Does Not a Month Make
The supply allowance for CGMs (HCPCS A4239) covers 30 days … which is different than a “month” as described in the proposed rule. The anniversary dates do not fall on the same calendar day of each month because not all months have 30 days. As a result, suppliers actually provide more than 12 units of service in the course of a year. They provide 12.17 units to be precise.
To arrive at the proper monthly reimbursement rate, Medicare must:
- Multiply the supply allowance rate by 12.17 to calculate the correct annual payment for supplies;
- Multiply the annual supply payment by five to determine the total supply allowance over the entire reasonable useful lifetime of the CGM device;
- Add the equipment cost to the total supply allowance; and
- Divide by 60 months.
That adds another $3.80 – about 1.5 percent – to the reimbursement rate.
Over the five-year life, that adds up.
Insulin Pump Rate
There is a similar, but more significant, error in the insulin pump rate calculation. Infusion sets (HCPCS A4224) are billed every seven days. Similar to the CGM supply allowance error, CMS assumes each month has exactly four weeks. That would only account for 48 of the 52.14 weeks in any given year. Adapting the formula for CGM rate calculation, the proper monthly reimbursement rate for insulin pumps under the proposed rule would increase by $8.69 to $234.91.
In summary, CMS calculated the following monthly rental rates in CMS-1828-P:
• CGMs: $272.69/month;
• Insulin pumps: $226.22/month
By my math, I think those rates should be:
• CGMs: $276.49/month;
• Insulin pumps: $234.91/month.
Andrea Stark is co-founder of MiraVista, LLC, Columbia, S.C. She is pictured above at Medtrade 2025.
