Modifier 91 | Repeat Clinical Diagnostic Laboratory Test Explained

Modifier 91 indicates a repeat lab test on the same day for the same patient.

1. What is modifier 91?

Modifier 91 describes a repeat clinical diagnostic laboratory test d on the same patienton the same day to obtain subsequent or multiple test results. This modifier indicates that the second test was not a duplicate but was medically necessary.

2. When to use modifier 91?

Modifier 91 should be used when a lab provider needs to obtain subsequent or multiple lab test results to monitor a patient’s condition during treatment better.

However, it is important to note that modifier 91 should not be used for repeated tests to confirm initial results due to testing problems with specimens or equipment or for any reason when a normal one-time result is all that is needed.

Additionally, modifier 91 should not be used with codes describing test results, such as glucose tolerance or evocative suppression tests.

3. Description

The official description of modifier 91 is “repeat clinical diagnostic laboratory test”.

4. Examples

Examples of procedures requiring modifier 91 include repeat glucose tests, lipid panel tests, and complete blood count (CBC) tests.

5. Documentation

When using modifier 91, it is essential to document the medical necessity of the repeat test in the patient’s medical record. The documentation should include the reason for the repeat test, the initial test results, and the repeat test results.

6. Billing

To bill for a repeat clinical diagnostic laboratory test with modifier 91, the lab provider should report the first test with the appropriate CPT® code and then the second test with the same CPT® code, appending modifier 91.

7. Common mistakes

One common mistake that medical coders make when using modifier 91 is using it for tests that were repeated to confirm initial results due to testing problems with specimens or equipment.

Another common mistake is using modifier 91 with codes that describe a series of test results. Medical coders should carefully review the documentation to avoid these mistakes and ensure that the repeat test was medically necessary.

8. Other modifiers related to modifier 91

Other modifiers related to modifier 91 include modifier 59, which indicates a distinct procedural service, and modifier 76, which indicates a repeat procedure or service by the same physician or provider.

9. Tips

When using modifier 91, medical coders should ensure that the repeat test was medically necessary and that the documentation supports using the modifier.

Additionally, medical coders should be familiar with other modifiers related to modifier 91 and their appropriate usage.