91

Modifier 91

Repeat Clinical Diagnostic Laboratory Test

Active

Global Period

Not Applicable

Modifier

Applies To

Clinical Laboratory Tests

Category

Use With

Laboratory

CPT Codes

What is Modifier 91?

Modifier 91 is used to report a repeat clinical diagnostic laboratory test performed on the same patient on the same day to obtain additional medically necessary information. The repeat test must be ordered because the patient's condition requires another measurement rather than because of equipment malfunction or specimen issues.

Modifier 91 is only reported with eligible laboratory tests.

When to Use

Repeat laboratory testing is medically necessary.
Patient condition changes during the same day.
Additional laboratory values are needed.
The same laboratory test is repeated for clinical management.

Documentation Requirements

Document medical necessity.
Record the reason for repeating the test.
Include laboratory results.
Maintain physician orders.
Support repeat testing in the medical record.

Examples

Example 1

A hospitalized patient has blood glucose levels monitored several times throughout the day. Modifier 91 may be appropriate when the same laboratory test is repeated for ongoing clinical management.

Example 2

A patient receiving anticoagulant therapy requires repeated coagulation testing during the same day to monitor treatment response.

Billing Tips

Use Modifier 91 only for repeat clinical laboratory tests.
Do not use Modifier 91 for quality control testing.
Do not report Modifier 91 when a specimen must be recollected due to error.
Verify the CPT code accepts Modifier 91.
Follow payer-specific laboratory billing guidelines.

Common Denial Reasons

Medical necessity not documented.
Modifier appended to an ineligible CPT code.
Repeat testing due to laboratory error.
Duplicate billing.
Insufficient supporting documentation.

Related Modifiers

Modifier 24

Unrelated E/M Service During the Postoperative Period

Modifier 25

Significant, Separately Identifiable E/M Service

Modifier 76

Repeat Procedure by the Same Physician

Modifier 77

Repeat Procedure by Another Physician

Additional Resources

Modifier 77 is used when another physician or qualified healthcare professional repeats a medically necessary procedure or diagnostic service. Accurate documentation of the repeat service and identification of the different provider help support proper reimbursement and reduce claim denials.

For comprehensive billing guidance, coding scenarios, documentation requirements, payer policies, modifier comparisons, and real-world examples, visit ModifierLookup.com for the complete Modifier 91 reference guide.