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CPT CODE 90999 Decoded – Dialysis Coding, Reimbursement & Expert Advice
- CPT code 90999 is a last-resort code for unlisted dialysis services.
- Always exhaust specific dialysis CPT codes before using 90999.
- Strong documentation is your best defense against denials.
- Medicare and private payers often reimburse 50–70% of comparable rates.
- Modifiers (GZ, 59) and ICD-10 codes (e.g., N18.6 – ESRD) are essential.
Accurate coding is the backbone of dialysis billing—and when no existing code fits, providers turn to CPT code 90999. This unlisted dialysis procedure code is both powerful and risky. Use it correctly, and you can secure proper reimbursement for innovative or unusual treatments. Use it incorrectly, and you risk claim denials, audits, or compliance issues.
This 2025 guide explains what CPT 90999 is, when to use it, documentation requirements, and how to avoid costly mistakes.
What is CPT 90999?
CPT 90999 is defined as:
Unlisted dialysis procedure, inpatient or outpatient.
Because it’s an unlisted procedure code, it should only be used when no specific CPT code exists for the dialysis service provided.
When CPT 90999 may apply:
- Experimental dialysis techniques not yet assigned a CPT code
- Hybrid dialysis treatments that combine multiple modalities
- Pediatric dialysis services with no direct equivalent code
- Research-based dialysis therapies under FDA clinical trials
If a standard code (e.g., 90935 hemodialysis, one evaluation or 90937 – prolonged hemodialysis) applies, you must use that instead.
When to Use CPT 90999 (Real-World Cases)
- Correct use: A provider performed laser-assisted solute clearance during dialysis. No listed CPT code covered the service. The claim used 90999 with a detailed physician narrative and supporting literature.
- Incorrect use: A clinic billed 90999 for nocturnal hemodialysis, even though CPT 90935 + 99356 (prolonged service) applied. Result: denial due to miscoding.
Documentation Requirements for CPT Code 90999
Because 90999 lacks a standard descriptor, payers require extra details:
- Procedure narrative: Describe exactly what was performed and why.
- Reason for unlisted code: Explain why no existing CPT code applies.
- Comparable service: Reference the closest related dialysis CPT code (e.g., “Similar to 90935 with added XYZ modification”).
- ICD-10 linkage: Common diagnoses include:
- N18.6 – End-stage renal disease (ESRD)
- N18.5 – Chronic kidney disease, stage 5
Supporting documents: Attach FDA approval status, research articles, or clinical trial data if applicable.
CPT Code 90999 Reimbursement in 2025
Reimbursement varies by payer, but here are common benchmarks:
- Medicare: Generally reimburses 50–70% of a comparable dialysis service. Prior authorization and GZ modifier may be required if coverage is uncertain.
- Commercial insurers: Payment policies vary. Anthem, UHC, and Aetna often pay a percentage of 90935 rates when 90999 is approved.
- Documentation is key: Claims without detailed narratives are almost always denied.
CPT 90999 Modifiers and Special Rules
- Modifier GZ – Used if you expect Medicare to deny the service for lack of medical necessity.
- Modifier 59 – Use if billing 90999 alongside other procedures to show distinct services.
- Most recent URR modifier: For claims tied to URR (urea reduction ratio) reporting, payers may request a modifier or documentation reflecting the reading. Example: If a patient’s URR is 61.4, this detail should be included in the claim documentation.
Top 3 Denial Reasons (and Fixes)
Reason: Missing narrative or documentation
Fix: Attach detailed procedure notes and a comparison to a listed CPT codeReason: No prior authorization
Fix: Request approval before billing experimental dialysis servicesReason: Bundling with E/M visits
Fix: Append modifier -59 if 90999 is separate from the E/M service
Conclusion
CPT code 90999 is a high-risk, high-reward billing tool. When used correctly, it ensures reimbursement for innovative or unique dialysis treatments. When misused, it leads to claim denials, compliance risks, and revenue loss.
At Express Medical Billing, we specialize in complex coding and dialysis billing services. Our team helps nephrology practices, dialysis centers, and hospital providers stay compliant with Medicare and commercial payer rules while maximizing reimbursements.
Contact us today for a free claims audit and see how we can help optimize your dialysis billing
Frequently Asked Questions (FAQs)
It is an unlisted dialysis procedure code, used only when no specific CPT code describes the service performed.
Reimbursement is payer-specific. Medicare generally pays 50–70% of a comparable code, while commercial payers may use different benchmarks.
Modifiers such as GZ (for Medicare non-covered services) and 59 (distinct procedure) may apply depending on the clinical situation.
CPT code 90999 is described as “Unlisted dialysis procedure, inpatient or outpatient.” It is used when no existing dialysis CPT code (such as 90935 or 90937) accurately represents the service performed.
To bill 90999, providers must submit:
- A detailed narrative describing the service
- Documentation showing why no existing CPT code applies
- ICD-10 codes such as 6 (ESRD) or N18.5 (CKD stage 5)
- Comparable service references (e.g., “Similar to 90935 but with modifications”)
Yes, but reimbursement is limited. Medicare typically pays 50–70% of a comparable dialysis code if documentation supports medical necessity. Prior authorization or medical review is often required.
The most common reasons include:
- Missing or vague documentation
- No prior authorization for experimental dialysis
- Incorrect bundling with other dialysis CPT codes
Providers can reduce denials by attaching detailed narratives and using modifiers correctly.
No, standard dialysis CPT codes (90935, 90937, 90989), 90999 has no fixed definition. It’s an “unlisted” procedure code used only when no other dialysis code applies.
