MODIFIER 91

Modifier 91 (Repeat Clinical Diagnostic Laboratory Test)

When a laboratory test is repeated due to medical necessity on the same day for the same patient we must append modifier 91 to the subsequent repeat lab procedure to avoid claim duplication.  

Modifier 91 would be used only with the Laboratory CPT codes.

Eg:  Glucose test is performed for a 54-year-old patient, which reveals hypoglycemia. Then they administer glucose to the patient and retest him 15 minutes later, at this point his glucose level is normal and the patient returns home.

In the above scenario, we have to code CPT 82947 (Glucose; quantitative, blood [except reagent strip]), followed by a second line item of 82947 (repeat procedure) with modifier 91.

We can also use modifier 91 when a Lab CPT codes are different but describes the same test for different analytes or organisms.

Eg: CPT codes 87804 and 87400 can describe influenza A or influenza B test.

If your payer recommends using modifier 91 to indicate that you performed the test twice, once for type A and once for type B, you may do so.

Inappropriate usage of modifier 91 if the lab test is repeated due to

   • To confirm initial results
   • Problems related to specimens or equipment
   • Any other reason when a normal, one-time reportable result is all that the physician needs for appropriate patient treatment.

Difference between modifier 59 and 91

If the same test was performed on two different anatomical sites, Instead of modifier 91 we should use modifier 59.

Eg: CPT 88305 Level IV–Surgical pathology, gross or microscopic examination

If two specimens are taken from Colon and Spleen its two different sites, append modifier 59 to the 2^nd line item.

If a second sample was taken from the same site, then append modifier 91 to the 2^nd line item. But we have to make sure repeat procedure is due to medical necessity.