Appropriate Use of Modifier 91

Appropriate Use of Modifier 91

Modifier 91 is defined by CPT® as representative of Repeat clinical diagnostic laboratory test, and is used to indicate when subsequent lab tests are performed on the same patient, on the same day in order to obtain new test data over the course of treatment. You can probably understand why it’s important to append appropriate modifiers when billing the same CPT two or even three times on the same day for the same patient. Imagine the claim from the payer’s perspective, and it would appear to be duplication of services, earning these claims an immediate denial.

Can you use modifier 59 and 91 together?

The 91 modifier is most often confused with the 59 modifier, used for distinct procedural service, and this is understandable. However, it’s important to note that while modifier 59 may make sense for many scenarios, modifier 91 allows billing to the highest specificity due to it being a modifier for lab tests only. Modifier 91 should be billed instead of 59 in most lab cases, so it’s important to learn how to use it appropriately.

Modifier 91 is not to be used for procedures repeated to verify results or due to equipment failure or specimen inadequacy. While 59 is used for differentiating two procedures while cannot be billed together on same day.

According to AAPC, presumptive identification of microorganisms is defined as identification by colony morphology, growth on selective media, Gram stains, or up to three tests (e.g., catalase, oxidase, indole, urease). Definitive identification of microorganisms is defined as an identification to the genus or species level that requires additional tests (e.g., biochemical panels, slide cultures). If additional studies involve molecular probes, chromatography, or immunologic techniques, these should be separately coded in addition to definitive identification codes (87140-87158). For multiple specimens/sites use modifier 59. For repeat laboratory tests performed on the same day, use modifier 91.”

Use of Modifier 91:

  • On a repeat lab test performed only to confirm initial results
  • When a lab test was repeated due to a problem with the specimen or equipment
  • When a series of lab tests would be better represented by another code; for example, glucose tolerance testing under code 82951 already includes 3 specimens under one code, so modifier 91 would not apply.

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