Modifier 91- Repeat Clinical Diagnostic Laboratory Test
Modifier 91 is used when the same laboratory test is repeated on the same day to obtain multiple test results.
What is Modifier 91?
Modifier 91 tells insurance payers that a repeat laboratory test was medically necessary and not a duplicate billing error.
When to Use Modifier 91
• A lab test must be repeated on the same day
• Multiple results are medically necessary
• The repeat test supports patient care decisions
• Testing is not due to equipment or specimen issues
Billing Example
A patient’s blood glucose levels are monitored multiple times during the same day due to changing clinical conditions. Modifier 91 may be appended to the repeated lab test code.
Documentation Tips
• Document medical necessity for repeat testing
• Include timing of repeated tests
• Clearly separate each test result
• Avoid duplicate billing documentation
Common Denial Reasons
• Repeat testing not medically necessary
• Duplicate claim submission
• Missing documentation
• Incorrect modifier usage
Related Modifiers
Frequently asked questions
What does Modifier 91 mean?
Modifier 91 indicates that a laboratory test was repeated on the same day for medically necessary reasons.
Can Modifier 91 be used for repeated equipment failures?
No. Modifier 91 should not be used when tests are repeated due to equipment or specimen issues.
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