KX is a line-level attestation that the clinical coverage criteria specified in a Medicare Local Coverage Determination (LCD) are documented in the patient's chart. It is most commonly invoked on durable medical equipment claims, but several MAC LCDs for Part B drugs — intravenous iron for non-CKD anemia, IVIG for covered indications, hyaluronic acid joint injections, and some off-label bevacizumab use — also require KX. Append KX only when the governing LCD names it; never as a generic “I have documentation” modifier.
KX is defined in the HCPCS Level II long descriptors as “Requirements specified in the medical policy have been met.” The operational authority is CMS Internet-Only Manual Publication 100-04 (Medicare Claims Processing Manual), Chapter 20, §50.6, and the modifier is invoked on a service-by-service basis by individual MAC Local Coverage Determinations and their companion Local Coverage Articles. Unlike JW or JZ — which CMS mandates nationally on every single-dose-vial claim — KX is only required where a specific LCD names it.
The modifier dates to the early 2000s and was originally a DME / orthotics tool. Over the past decade, MACs have expanded its use into Part B drug coverage as a way to require provider attestation to LCD criteria without requiring a separate prior authorization or attached documentation. The compromise is that KX shifts the documentation burden to post-payment audit: the MAC pays the claim if KX is present, then samples charts later to verify the attestation. That makes KX a high-leverage modifier for both the practice (it unlocks payment) and the auditor (it identifies the claims worth probing).
The most common Part B drug categories where MAC LCDs require KX are: intravenous iron (Feraheme / J1439, Injectafer / J1437, Venofer / J1756, ferumoxytol / J1439) under LCDs for non-CKD iron deficiency anemia, attesting to TSAT < 20% and ferritin < 100 ng/mL plus oral-iron failure or contraindication; intravenous immunoglobulin (Privigen / J1459, Gammagard / J1569, Gamunex / J1561) under LCDs for primary immunodeficiency, CIDP, ITP, and other covered indications, attesting to the covered diagnosis plus required clinical markers; hyaluronic acid intra-articular injections for osteoarthritis of the knee; and certain MAC policies covering off-label bevacizumab uses. The exact list is in motion as MACs publish, retire, and revise LCDs; always verify the live LCD for your specific MAC and effective date.
The top KX failure mode is reflexive use: a practice configures the billing system to auto-append KX on every iron or IVIG claim because “the LCD requires it,” without per-chart verification. When the audit comes, every claim is exposed. KX is per-patient, per-encounter, attesting to chart-level facts — not a flag on the drug.
KX is overwhelmingly a Medicare Part B modifier with heavy variation by MAC. Commercial payers rarely require it; some accept it silently as a no-op, others ignore it entirely. The table below summarizes the typical posture; individual policies override.
| Payer | KX required on Part B drugs? | Notes |
|---|---|---|
| Medicare (Part B) — MAC LCDs | Yes, where LCD names it | Heavy variation by MAC and by drug. IV iron LCDs in several MAC jurisdictions require KX for non-CKD iron deficiency anemia attestation. IVIG LCDs frequently require KX. Hyaluronic acid LCDs frequently require KX. Always pull the live LCD for the MAC and date of service before billing. |
| UnitedHealthcare | No (with exceptions) | UnitedHealthcare medical policies generally do not require KX. UHC's Medicare Advantage plans inherit LCD criteria from the underlying MAC and may require KX on those claims; UHC commercial plans typically do not. |
| Aetna (CVS Health) | No (with exceptions) | Aetna medical-policy bulletins rarely name KX. Aetna Medicare Advantage follows the relevant MAC LCD where applicable. CVS Specialty does not impose KX on dispense reports. |
| Cigna / Express Scripts | No | Cigna commercial policies do not require KX. Cigna Medicare Advantage follows the MAC LCD. Accredo dispense workflow does not generate KX. |
| Humana | Conditional | Humana's MA-heavy book inherits MAC LCD requirements; KX applies on those claims. Humana commercial PPO and HMO policies typically do not require KX. |
| Denial pattern | What it means | Fix / appeal language |
|---|---|---|
| KX appended without supporting chart documentation | Post-payment review pulls the chart for a KX-attested claim and finds the LCD criteria are not all documented. Recoupment plus extrapolated repayment exposure across the look-back sample. | Voluntarily refund and remediate. Internal-controls fix: require a checklist tied to the LCD criteria before any KX is appended. Appeal language only works when the documentation actually exists and the reviewer missed it: “The chart documents [criterion 1] on [date], [criterion 2] on [date], and [criterion 3] on [date], satisfying the [LCD ID] coverage criteria attested to by modifier KX. Records attached.” |
| KX missing on a service the LCD requires it for | Claim submitted for a covered service under an LCD that mandates KX, but the modifier is absent. The MAC denies as not meeting coverage criteria because the required attestation is not present. | Resubmit a corrected claim with KX appended. Appeal language: “The submitted claim for [J-code] meets the coverage criteria specified in [LCD ID]. The corrected claim appends modifier KX to attest that [specific criteria from the LCD] are documented in the medical record for date of service [DOS]. The relevant chart pages are attached for confirmation.” |
| KX used on a service no LCD requires it for | KX appended to a claim where no LCD names the modifier. The claim usually adjudicates and pays (KX is generally harmless on non-LCD-governed services), but the pattern is a soft audit-triage flag, and KX on non-LCD claims provides no protective value. | No fix needed for the specific claim. System-level fix: tighten the billing rule so KX is appended only when the governing LCD invokes it. Reflexive KX use across all claims for a drug undermines the modifier's signal value and increases audit attention without improving coverage outcomes. |
| KX on retired or superseded LCD | Claim cites an LCD that was retired or superseded prior to the date of service. The KX attestation is technically pointing to a policy that no longer governs, and the MAC may deny or recoup on review. | Identify the active LCD for the date of service and resubmit with KX where the active LCD still requires it. If the new LCD does not require KX, resubmit without it. Appeal language: “The corrected claim references the active LCD [new LCD ID] for date of service [DOS]; modifier KX is [appended / not appended] per the criteria of the live LCD.” |
| KX without the underlying frequency or quantity criteria met | KX appended but a frequency edit (e.g., one hyaluronan course per knee per 6 months) is independently violated. KX attests to clinical criteria; it does not override frequency or units-per-day edits. | Verify the LCD's quantity/frequency limits and resubmit within them. If a clinically warranted exception applies, document the medical necessity narrative and pursue an LCD-specific exception path; KX alone will not unlock a frequency override. Appeal language: “The corrected claim falls within the [LCD ID] frequency limit of [N per interval]; KX attests to the clinical criteria, and the quantity billed conforms to the LCD edit.” |
Use KX when a Medicare Local Coverage Determination (LCD) or related Local Coverage Article instructs you to append it to attest that the LCD's clinical coverage criteria are documented in the medical record. The triggering language is typically “append modifier KX to indicate documentation of [criterion] is on file.” KX is LCD-specific, so the requirement varies by MAC and by service.
Common Part B drug categories where MAC LCDs invoke KX include intravenous iron products for non-CKD iron deficiency anemia (e.g., Feraheme, Injectafer, Venofer), intravenous immunoglobulin for specific covered indications (e.g., Privigen, Gammagard), hyaluronic acid intra-articular injections, and certain off-label uses of bevacizumab. The exact list changes as MACs publish, retire, and revise LCDs; verify the live LCD for your MAC before billing.
KX is defined by CMS and used primarily on Medicare Part B claims to attest LCD criteria are met. A handful of commercial payers and state Medicaid programs accept or require KX in their own medical policies, but the modifier originates from the LCD framework and has limited applicability outside Medicare. Verify each commercial payer's policy before appending KX to a non-Medicare claim.
No. KX is an attestation that the LCD criteria are met and documented; it is not a substitute for the documentation itself. The MAC may pay the claim on submission and then request the records during a post-payment review. If the chart does not support the KX attestation, the payment is recouped and the practice faces audit exposure proportional to the volume of KX-attested claims in the look-back period.
KX attests to whatever the specific LCD names as its coverage criteria. For IV iron under several MAC LCDs, the chart must show iron-deficiency labs (TSAT, ferritin) meeting LCD thresholds plus failed or contraindicated oral iron. For IVIG, the chart must show the covered diagnosis, the immunoglobulin level (if required), and recurrent-infection documentation appropriate to the indication. Read the LCD's coverage criteria section and the related billing-and-coding article verbatim — the KX attestation must match those criteria, not a paraphrase.
KX is a high-leverage attestation, which means it is also a high-leverage audit target. RAC, SMRC, UPIC, and MAC medical-review contractors all probe KX claims. The standard audit pattern is a record request for a sample of KX-attested claims; if the chart does not support the attestation, the auditor extrapolates the error rate across the population for a recoupment demand. Practices that bill KX reflexively on every claim for a given drug, without chart-level criteria verification, are the highest-risk profile.
GA, GZ, and GY are Advance Beneficiary Notice (ABN) modifiers tied to liability shifting when a service is or may be denied. KX is a coverage-criteria attestation tied to LCD compliance. They serve different functions: KX says “this service should be covered because the LCD criteria are met”; GA/GZ/GY address the scenario where coverage is uncertain or denied and the question is who pays. They can coexist on a claim where the LCD criteria are met but the patient was also given an ABN, but they are not interchangeable.
Only when the commercial payer's medical policy explicitly accepts or requires KX. Many commercials ignore KX silently (it neither helps nor hurts adjudication); a few align with the Medicare LCD framework and accept KX as an attestation; very few require it. Append KX on a commercial claim only when the payer's policy bulletin names it. Otherwise, document the clinical criteria in the chart and on the prior authorization, not via KX.
All sources are publicly available federal publications or paraphrased from trade-association educational materials. The methodology by which we resolve source disagreements is described in the Methodology.