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Coding Confusion: Avoiding Denials

It is not uncommon for multiples of the same CPT to be denied as duplicates. To prevent the denials, CMS approved the use of the -91 modifier to indicate that the second and each additional code reported for reimbursement is not a duplicate. Another option is the -59 modifier. The latter modifier indicates that separate and distinct services were provided and reported with appropriate codes. These modifiers are especially important when payment limits have been established for multiples of the same procedural code or when CCI edits disallow payment for certain combinations of codes.

-91 Modifier

As previously mentioned, this modifier indicates a repeat of the same test on the same day for subsequent results. It is not to be used when confirming initial results, when problems exist with tests or equipment, or when alternate codes describe a series of tests. Originally established by CMS as the modifier-QR in 1998, it was adopted by the AMA and converted to the -91 modifier in 2000. Its use is limited to the laboratory discipline.

CMS originally indicated that the modifier should be used with repeat CPT codes that were billed on the same patient within the same 24 hour period and should be limited to use with those codes that were reimbursed according to the Clinical Laboratory Fee Schedule. The first test performance was to be billed on a separate claim line by indicating the appropriate CPT code without the -91 modifier and a "1" in the unit column. Billings for repeat determinations were to be indicated on the next claim line along with the repeated CPT code attached to the -91 modifier and the appropriate number of units.

Modifier -91 Examples

Electrolytes are ordered for a patient in the emergency department and the physician orders two more sets of electrolyte determinations during the same 24-hour period (medical necessity justified). The first set of analyses would be coded with CPT 80051 and billed on one claim line with a "1" in the unit column. The remaining two determinations would be coded with CPT 80051-91 on the following claim line and a "2" in the units column.

A CBC is ordered for a patient in the morning and a hematocrit and hemoglobin (H&H) are ordered later in the day. The automated CBC and differential are billed with CPT 85025 and the H&H are reported with CPT 8501491 and 8501891 (modifier attached to both).

-59 Modifier

Under certain circumstances, there may be a need to indicate that a service provided is distinct or independent from other services reported on the same day, services not normally reported together are appropriate reported under the circumstances, or that the reported services represent a different encounter, procedure, site or organ system. The -59 modifier is an "off shoot" of the -GB modifier, a Level II modifier assigned by CMS in 1996, as a result of the Correct Coding Initiative (CCI), to indicate when a provider should legitimately bypass CCI bundling or "mutually exclusive" edits.

The -GB modifier proved valuable and was adopted by CPT in 1997. Because CPT modifiers are numerical, -GB was deleted and -59 created as a replacement. Knowing the background of the modifier is important in understanding that its use requires supportive documentation. Our firm believes that excessive use "raises red flags." Thus, the modifier should be used sparingly and only when it is the most appropriate modifier. CPT further states that "when another already established modifier is appropriate, it should be used rather than modifier -59. Only if no more descriptive modifier is available, and the use of modifier -59 best explains the circumstances, should modifier -59 be used."

Modifier -59 Examples

CCI edits do not allow CPT 88104 through 88107 (family of codes for washings, brushings and fluids) to be billed with CPT 88108 (concentration technique for fluid, washing or brushing along with smears and interpretation). These codes are attached to "subscript 1," which does allow the use of modifiers, if appropriate. If a sputum sample was coded with CPT 88108 and another discharge was submitted on slides and coded with CPT 88104, the -59 modifier would be appropriately added to CPT 88104 to indicate two separate and distinct specimens were analyzed.

Two microbiology cultures that are identified with the same CPT but reflect two different specimens should use the -59 modifier for the second culture.

Modifier Confusion

The Medicare Claims Processing Manual (Section 20.9) now indicates that if multiple services are performed on different cytopathology specimens (CPT 88104-88108 or 88160-88162), the -91 modifier is appropriate. Using previous clarifications from CMS, we think the -59 modifier is more correct. Further, CCI instructions for laboratory and pathology indicate that the -59 modifier is appropriate.

If an infectious agent detected by molecular diagnostics technology is billed with molecular diagnostic codes that identify a separate test on the same specimen, is -91 or -59 correct for the second test? Are all codes for the separate codes attached to a modifier? We would use -91 on all codes for the second test.


Modifier instructions vary from one Medicare Contractor to another and from payer to payer. Gather input and instructions from your various payers and establish a policy that clarifies and standardizes the approach that a facility employs for assigning modifiers. Remember to be frugal when assigning -59.

Diana Voorhees is principal in DV & Associate Inc., Salt Lake City, which makes no representation, guarantee or warranty, expressed or implied, that the information provided is free from error, and will bear no responsibility or liability for results or consequences of its use. She can be reached at

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