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Modifier Coding Alert

Laboratory Tests:

Recognize 2 Lab Modifiers To Capture Same-day Test Payment

Re-running lab tests to confirm results and using modifier 91, won’t result in payment.

If your office doesn’t have the capability to handle laboratory tests or you have patients that require multiple lab tests be run on the same day, you need to be comfortable with modifiers 90 and 91 and be able to tell the difference between the two. 

Find that comfort and confidence here by identifying the modifier confusions and honing your know-how.

Unravel Your Modifier 91 Confusion

Your confusion with modifiers 90 (Reference [outside] laboratory) and 91 (Repeat clinical diagnostic laboratory test) can occur when your patient’s course of treatment requires repeating a laboratory test on a specimen from one specific site, on the same day in order to obtain multiple test results. Using modifier 91 is correct in this situation.

“Both 90 and 91 modifiers apply to lab tests, but otherwise, they serve very distinct purposes,” explains Kent Moore, senior strategist for physician payment at the American Academy of Family Physicians (AAFP) in Kansas City, Mo. “Modifier 90 is used to identify lab tests that your practice did not do itself. Modifier 91 is used to identify a second (or third, etc.) iteration of a lab code billed on the same date for the same patient when repeat testing is appropriate (as outlined in the descriptor of the modifier).” 

Another modifier you may sometimes use in error when modifier 91 is the correct choice is modifier 59 (Distinct procedural service). When the same lab procedure is done but it involves different specimens or cultures that are obtained from different sites, 59 is your correct choice. 

“I think prior to modifier 91 being available, labs tried using 59 or multiple units and had difficulty getting paid — then they came out with 91 and the labs rejoiced,” quips Laureen Jandroep, CPC, CPC-I, CMSCS, CHCI, senior instructor at in Oceanville, N.J.

You may also find yourself stumped by when to use modifier 91 versus modifiers 76 (Repeat procedure or service by same physician or other qualified health care professional) or 77 (Repeat procedure or service by another physician or other qualified health care professional). Although modifiers 76 and 77 are for repeated services, they do not apply when your physician performs repeat laboratory tests. In these situations, you should always attach modifier 91.

“Those modifiers are for repeat procedures — 76 for the procedure being repeated by the same provider and 77 for being repeated by a different provider,” clarifies Suzan Hauptman, MPM, CPC, CEMC, CEDC, manager of physician compliance auditing at Allegheny Health Network in Pittsburgh, Penn.

Indicate You Process Your Lab Work in an Outside Lab With Modifier 90

When your practice isn’t structured to handle laboratory testing and you need to have tests performed by a party other than the treating or reporting physician or other qualified health care professional, you will identify the procedure with modifier 90.

Example: A patient presents to the office for an automated complete blood count. The blood is drawn by office staff, and the specimen is sent to an outside lab for processing. Appropriate coding in this case is 36415(Collection of venous blood by venipuncture) for the blood draw and 85027-90 (Blood count; complete [CBC], automated [Hgb, Hct, RBC, WBC and platelet count]) for the test. Append modifier 90 to the CPT® code describing the CBC to indicate that although the provider is reporting the procedure, it actually was performed by an outside lab.

In such cases, according to professionals, the lab generally will bill the physician’s office for its service, and the office will, in turn, bill the patient for the lab.

“Modifier 90 is hardly used anymore since consolidated billing,” Jandroep says. “It used to be that physician’s offices would bill all lab work even when performed by an outside lab. They would attach modifier 90 to the lab CPT® code, for instance 80051 (Electrolyte panel). They would also check ‘yes’ in box 20 on the 1500 form that says ‘Outside Lab’ and provide the labs address on the bottom of the claim form in box 32.”

Good practice: Consult third-party payers before reporting modifier 90; exact usage rules vary by payer.

Processing Patient’s Same-Day Lab Work Requires Modifier 91

A laboratory test may need to be repeated on the same day during a patient’s treatment in order to obtain subsequent test results. When it is, you will report the procedure with modifier 91. Using modifier 91 indicates to payers that a repeated diagnostic laboratory test was distinct or separate from a lab panel or other lab services performed on the same day.

Strategy: Multiple laboratory services provided to a patient on one day by the same provider may appear to be incorrectly coded, when in fact the services may have been performed as reported. Because these circumstances cannot be easily identified, modifier 91 was established by CMS to permit claims of such a nature to bypass correct coding edits.

Example: You have a patient with high blood pressure who has been on a low-salt diet. He receives a plasma renin activity (PRA) test (84244, Renin) in the morning in the supine position. Because physicians may use variations in PRA levels due to time of day and patient position to evaluate certain conditions, such as hyperaldosteronism, they may order a repeat renin in the afternoon with the patient standing upright for a period of time. If your physician does this, and it’s clearly illustrated in the documentation, report the second 84244 with modifier 91 to indicate that the lab performed two separate renin assays for the same patient on the same day.

Manage panels and repeat tests: You should use modifier 91 even if you conduct a lab test as part of a panel and repeat the test separately at another time of day. On rare occasions, it may be necessary to assign modifier 91 even though you’re reporting two different codes because they include the same lab test for subsequent results.

For instance: If the lab performs an electrolyte panel to evaluate acidosis and the physician later orders a follow-up bicarbonate test, report both 80051 (Electrolyte panel) and 82374 (Carbon dioxide [bicarbonate]). Append modifier 91 to 82374 to specify that you repeated the bicarbonate.

The laboratory may bill the physician directly for the tests it did, and then the physician’s office will use modifier 90 to indicate which of the tests an outside laboratory performed.

Tip: Here’s an easy way to remember the difference between modifiers 90 and 91, coined by Hauptman. Modifier 91 ends with the number 1, meaning the one practice did the test twice, whereas modifier 90 ends with the number 0, meaning the practice didn’t do the test again but the test was done again by another outside facility, she explains. To read more about modifiers 90 and 91, take a look at

Avoid Modifier 91 When Equipment Fails

When your physician re-runs tests to confirm initial results due to testing problems with specimens or equipment or for any other reason when a normal one-time reportable result is all that is required, you would not use modifier 91. Modifier 91 is only used for lab tests performed more than once on the same day, on the same patient, when deemed medically necessary in consideration of the procedure.

Warning: Don’t use this modifier when other code(s) describe a series of test results, for instance glucose tolerance tests, or evocative/suppression testing. 

CPT® guidelines state that if a physician requests multiple tests to be run, but a single code describes the tests, you should only report one code, and attaching modifier 91 would not apply. 

Example: Code 82951 (Glucose; tolerance test [GTT], 3 specimens [includes glucose]) includes three specimens so if three specimens were obtained during the encounter, you only report 82951 and do not attach a modifier.