Wiki Cpt 88185

I found a bunch of LCDs stating:
"In accordance with CMS Ruling 95-1 (V), utilization of these services should be consistent with locally acceptable standards of practice.

Routinely performing more than 20 analyses (or units of 88185) per specimen is not expected by Medicare.

Notice: This LCD imposes utilization guideline limitations. Despite Medicare's allowing up to these maximum number of units of service, each patient’s condition and response to treatment must medically warrant the number of services reported for payment. Medicare requires the medical necessity for each service reported to be clearly demonstrated in the patient’s medical record. Medicare expects that patients will not routinely require the maximum allowable number of services. In specific, many “routine” (e.g., anemia of unknown etiology) evaluations will be expected to require a relatively few number of cell surface markers, which, in the absence of more severe pathology, should not typically require further flow cytometry analysis. Conversely, for the appropriate diagnosis of some newly-discovered neoplasms (e.g., leukemias), there may be special classification challenges where a progression of cell surface marker evaluations becomes medically necessary for that difficultto-diagnose neoplasm. In other words, the billing of 88185 must reflect the thoughtful, step-wise (i.e., algorithmic) approach to evaluating specimens in marked contradistinction to any use of standard “global-type” cell surface marker testing panels, which do not carefully adhere to this principle of thoughtful, sequential diagnostic reasoning."

I'd say there's no "maximum" per se, instead it's more DX and medically necessary driven. You'd have to have the documentation to prove more than a few markers were necessary and appeal any denials.