Pathology/Lab Coding Alert

Question: When should we use modifier 91 instead of modifier 59?  

Kentucky Subscriber

Answer: Reserve modifier 91 (Repeat clinical diagnostic laboratory test) for claims involving clinical lab tests, which are generally procedures paid on the Clinical Laboratory Fee Schedule, not the Physician Fee Schedule. Another restriction for 91 is that the reason for repeating the same lab test on the same date must be that it is medically necessary to obtain subsequent test results. You shouldn’t use the modifier if the lab repeats the test to confirm results, or due a technical problem or for quality assurance.

For instance: If the clinician orders a urinalysis (81000, Urinalysis, by dip stick or tablet reagent for bilirubin, glucose, hemoglobin, ketones, leukocytes, nitrite, pH, protein, specific gravity, urobilinogen, any number of these constituents; non-automated, with microscopy) for a patient who is severely dehydrated, and orders a urinalysis later that day following intravenous treatment, you should report 81000 and 81000-91.

On the other hand, you may use modifier 59 (Distinct procedural service) or a similar modifier when your pathologist performs two medically necessary procedures on specimens from different anatomic sites or different surgical sessions. You need the modifier when the Correct Coding Initiative (CCI) edits bundle the codes, but the clinical circumstances indicate that the services are separate.

For instance, if the pathologist examines a thyroid cyst aspiration specimen using cellular-enhanced liquid cytology (88112, Cytopathology, selective cellular enhancement technique with interpretation (eg, liquid based slide preparation method), except cervical or vaginal) and also evaluates a lymph node FNA specimen (88173, Cytopathology, evaluation of fine needle aspirate; interpretation and report), you should code 88173 and 88112-59.