Procedure Coding: When to Use the 91 Modifier

Procedure Coding: When to Use the 91 Modifier

This is part of the Modifier Series, the articles include:


We all know how difficult it can be to get payers to reimburse appropriately when a claim is sent completely clean. But forget just one modifier and you can easily fall into a tedious cycle of denials, corrected claims and appeals – nobody’s idea of a fun time. In order to prevent further frustration around getting your claims and providers paid, it’s important to have accurate coding knowledge on your side.

In discussing the 91 modifier, we’ll clarify how it applies to repeated lab tests done on the same day for the same patient. Why does this matter? Specifically, because modifier 91 deals with showing that a repeated service was done with intent and should be a payable service.

Defining 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.

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.

To provide more insight into when you’d need to apply the 91 modifier, and to underline the importance of its appropriate use, here are some clarifying examples of modifier 91 at work.

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Clinical Scenarios

Modifier 91 Example 1
A patient is seen in the ER, where her physician orders a blood glucose meter lab test. Later during the same visit, the physician orders a second BGM lab test in order to identify separate accession and result numbers. Appropriate coding of this encounter would be: 82962; 82962-91.

Modifier 91 Example 2

An elderly male patient with diabetic ketoacidosis had multiple blood tests performed to check his potassium levels following potassium replacement and low-dose insulin therapy. After the initial potassium results, three subsequent blood tests were ordered and performed on the same date to monitor his blood levels over the course of the potassium treatment. Coding for this scenario is:

84132 Potassium; serum, plasma or whole blood

84132-91; 84132-91; 84132-91

When not to use 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.

Summary

The 91 modifier may have its points of confusion, but a little clarification can go a long way.

As the standard rule for billing modifiers regardless of their individual use, supporting documentation of the services performed should be maintained in the patient’s medical record. This documentation will need to do more than prove medical necessity. It also needs to substantiate that the repeat lab tests were performed separately and appropriately to rule out any questioning from the payer.

Sources:

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