Pathology/Lab Coding Alert

Question: We-ve started using modifier GD to override the MUE limits for flow cytometry when medically necessary. We recently received a denial from our carrier for a panel with 24 markers when we used the modifier with 88185. The denial said that the GD modifier is not recognizable. How can we report this flow panel so that we can get paid?

Tennessee Subscriber

Answer: You should not need to use a modifier to report a single flow cytometry panel with 24 markers. The correct coding is as follows:

- 88184 -- Flow cytometry, cell surface, cytoplasmic or nuclear marker, technical component only; first marker

- +88185 x 23 -- - each additional marker (List separately in addition to code for first marker)

- 88189 -- Flow cytometry, interpretation; 16 or more markers.

You can see from the code definition that you should list one unit of add-on code +88185 for each marker beyond the first -- 23 units in your example.

Watch MUEs: You are correct that CMS has listed medically unlikely edit (MUE) limits for some flow cytometry codes. But the edits don't restrict the number of markers per panel, they only restrict the number of panels.

By placing a limit of -1- on the -first marker- code (88184) and each of the -interpretation- codes (88187-88189), the MUEs effectively limit you to reporting a single flow cytometry panel for a patient on a given day.

There is no published MUE limit for +88185, so unless this is one of the codes that Medicare has identified as a -confidential- MUE value, you should not get denials based on an MUE limit.

Modifiers uncertain: Although CMS introduced modifier GD (Units of service exceed medically unlikely edit [MUE] value and represent reasonable and necessary services), the agency has not published any instructions about using the modifier. CMS has provided a -frequently asked question- about MUEs that indicates you can override the limits for medically necessary procedures using a modifier such as 91 (Repeat clinical diagnostic laboratory test) or 59 (Distinct procedural service).

Mystery remains: You should seek direction of your payer regarding why they-ve denied this particular claim, and which modifier, if any, the insurer wants you to use in rare instances when you do need to override an MUE limit.