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Aquaporin-4 (AQP4) antibodies serve as a highly specific and sensitive serological marker for neuromyelitis optica (NMO), which is an autoimmune, inflammatory, demyelinating disease affecting the central nervous system (CNS). NMO is recognized as a spectrum disorder that primarily impacts the optic nerves and spinal cord, but it can also involve the brain. The presence of these antibodies is critical as they can lead to severe clinical manifestations, including blindness, weakness or paralysis in the limbs, uncontrollable vomiting or hiccups, painful spasms, and dysfunction of the bladder or bowel. In pediatric patients, NMO may present with seizures or even coma. Flare-ups of the disease can result in irreversible vision loss and mobility issues. The antibodies, often referred to as NMO-IgG or AQP4, represent the first biomarker identified for any form of CNS inflammatory demyelinating disease. Their detection is essential for distinguishing NMO from multiple sclerosis (MS), as AQP4 antibodies are typically present in NMO but absent in classical MS. The testing process involves obtaining a venous blood sample from the patient, which is then analyzed using flow cytometry, specifically fluorescence-activated cell sorting (FACS). This advanced technique allows for the sorting of individual cells based on their characteristics. In the laboratory, human embryonic kidney (HEK) cells are modified to express green fluorescent protein (GFP)-tagged AQP4 and are mixed with untransfected HEK cells. The patient's serum sample is introduced, followed by the addition of a secondary anti-human antibody that is conjugated with fluorescein isothiocyanate, which binds to the human antibodies present in the serum. As the cells pass through a laser beam, their fluorescence is measured, and they are sorted based on whether they carry the fluorescently tagged human antibody. Additional titration studies may be conducted to determine the dilution factor at which specific fluorescence remains detectable, providing a semi-quantitative result for the presence of AQP4 antibodies.
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The testing for aquaporin-4 (AQP4) antibodies is indicated for the following conditions:
The procedure for testing AQP4 antibodies involves several detailed steps:
After the procedure, the patient may not require any specific post-procedure care, as the blood sample collection is minimally invasive. However, it is essential to monitor the patient for any immediate adverse reactions to the blood draw. The results of the AQP4 antibody test will be analyzed and reported, which can take several days. Clinicians will use these results to inform diagnosis and treatment decisions for conditions such as neuromyelitis optica. Patients should be advised to follow up with their healthcare provider to discuss the results and any necessary next steps in their care.
| Short Descr | AQAPRN-4 ANTB FLO CYTMTRY EA | Medium Descr | AQUAPORIN-4 ANTIBODY FLOW CYTOMETRY EACH | Long Descr | Aquaporin-4 (neuromyelitis optica [NMO]) antibody; flow cytometry (ie, fluorescence-activated cell sorting [FACS]), each | Status Code | Statutory Exclusion (from MPFS, may be paid under other methodologies) | Global Days | XXX - Global Concept Does Not Apply | PC/TC Indicator (26, TC) | 9 - Not Applicable | Multiple Procedures (51) | 9 - Concept does not apply. | Bilateral Surgery (50) | 9 - Concept does not apply. | Physician Supervisions | 09 - Concept does not apply. | Assistant Surgeon (80, 82) | 9 - Concept does not apply. | Co-Surgeons (62) | 9 - Concept does not apply. | Team Surgery (66) | 9 - Concept does not apply. | Diagnostic Imaging Family | 99 - Concept Does Not Apply | CLIA Waived (QW) | No | APC Status Indicator | Conditionally packaged laboratory tests | Type of Service (TOS) | 5 - Diagnostic Laboratory | Berenson-Eggers TOS (BETOS) | none | MUE | 1 |
| 90 | Reference (outside) laboratory: when laboratory procedures are performed by a party other than the treating or reporting physician or other qualified health care professional, the procedure may be identified by adding modifier 90 to the usual procedure number. | 59 | Distinct procedural service: under certain circumstances, it may be necessary to indicate that a procedure or service was distinct or independent from other non-e/m services performed on the same day. modifier 59 is used to identify procedures/services, other than e/m services, that are not normally reported together, but are appropriate under the circumstances. documentation must support a different session, different procedure or surgery, different site or organ system, separate incision/excision, separate lesion, or separate injury (or area of injury in extensive injuries) not ordinarily encountered or performed on the same day by the same individual. however, when another already established modifier is appropriate it should be used rather than modifier 59. only if no more descriptive modifier is available, and the use of modifier 59 best explains the circumstances, should modifier 59 be used. note: modifier 59 should not be appended to an e/m service. to report a separate and distinct e/m service with a non-e/m service performed on the same date, see modifier 25. | 91 | Repeat clinical diagnostic laboratory test: in the course of treatment of the patient, it may be necessary to repeat the same laboratory test on the same day to obtain subsequent (multiple) test results. under these circumstances, the laboratory test performed can be identified by its usual procedure number and the addition of modifier 91. note: this modifier may not be used when tests are rerun 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. this modifier may not be used when other code(s) describe a series of test results (eg, glucose tolerance tests, evocative/suppression testing). this modifier may only be used for laboratory test(s) performed more than once on the same day on the same patient. | GA | Waiver of liability statement issued as required by payer policy, individual case | GZ | Item or service expected to be denied as not reasonable and necessary |
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| 2022-01-01 | Added | Code added |
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