CS modifier is a two-character code listed in the HCPCS Level II system. Most medical billers think the modifier was introduced during the COVID-19 pandemic, but its actual usage began a decade earlier. It was initially used during a federal disaster response.
Today, although the COVID-19 Public Health Emergency (PHE) ended in May 2023, its application remains confusing for many billing professionals.
However, we will clear every doubt regarding modifier CS in this guide, discussing its official definition, the different contexts in which the modifier was or is used, and the existing rules for
its application to a Medicare claim. Let’s start.
CS Modifier – Description
According to the Centers for Medicare & Medicaid Services (CMS), the CS modifier is a HCPCS Level II modifier appended to specific qualifying services for claims processing and reimbursement.
The HCPCS Level II is the national coding system used for reporting supplies, items, and services not described by CPT codes. It includes 5-character codes as well as 2-character modifiers.
The CMS is responsible for maintaining and revising these modifiers. As per the original definition, the CS modifier is appended when:
“An illness, injury, or condition caused by or exacerbated by the effects, direct or indirect, from the 2010 oil spill in the Gulf of Mexico, requires an Item or service related, in whole or in part, but not limited to, subsequent clean-up activities.”
Simply put? The modifier was initially appended to medical service codes for conditions related, in whole or in part, to the 2010 Gulf of Mexico oil spill or its cleanup.
Note: This use is now largely historical and rarely encountered in current billing.
The Two Sides of the CS Modifier
The Gulf oil spill description of the CS modifier may seem surprising to those who first learned about this modifier during the pandemic.
Historically, the modifier has had two distinct uses, but the CMS introduced the modifier in response to the Deepwater Horizon disaster to identify related services for Medicare claims.
Meaning, it allowed the CMS to identify and process Medicare claims related to the disaster. Medical billers were first applying the modifier to Medicare fee-for-service claims on or after April 20, 2010, when the Horizon rig exploded.
Later, during the COVID-19 pandemic, the same two-character modifier flagged cost-sharing waivers under federal COVID-19 policy. In this context, CMS described the CS modifier, documented in CMS MLN Matters SE20011, as:
“Cost-sharing for COVID-19 testing-related services resulting in an order for or administration of a COVID-19 test.”
Both of these uses are applicable to the CS modifier, depending on the different billing situations, which is why accuracy is imperative.
What Changed After the COVID-19 Emergency Ended?
The changes after the COVID-19 pandemic are details that most billing teams miss. The official records of the United States Department of Health and Human Services (HHS) state the COVID-19 Public Health Emergency officially ended May 11, 2023.
According to the CMS COVID-19 PHE fact sheet, specific coverage for over-the-counter and laboratory-based COVID-19 diagnostic tests may no longer be applicable. Moreover, cost-sharing rules for COVID-19 testing-related services are now following a standard benefit structure again.
The Families First Coronavirus Response Act (FFCRA) cost-sharing waiver that drove the COVID-era use of the modifier was tied directly to the PHE and sunset with it.
What Billing Teams Should Remember?
The CS modifier is still mentioned in the HCPCS coding system, but is no longer broadly applicable after May 11, 2023, and is now limited to specific payer policies or legacy claims. On the other hand, the Gulf oil spill-related description remains in the HCPCS manual but is rarely used in current billing practice.
Therefore, before billers append the CS modifier to a Medicare claim, they must confirm its validity with the appropriate Medicare Administrative Contractor (MAC) and payer policy.
Appropriate Use Cases for CS Modifier
The CS modifier is generally no longer applicable for routine current claims after PHE, regardless of patient status.
Nonetheless, it is a necessary tool for medical coders working with legacy data or legal financial reviews, and should only be used in billing for payer-specific requirements.
Symptomatic Patient Visit Leading to COVID Test
Imagine a physician’s office visit during the COVID-19 PHE, where a 42-year-old Medicare patient presented with cough, fever, and shortness of breath.
The healthcare provider began with an evaluation and management (E/M) service (CPT code 99213) and ordered a SARS-CoV-2 nucleic acid amplification test (reported with CPT code 87635).
The test was performed to rule out or confirm COVID-19. Thus, according to the FFCRA and CARES Act rules, the visit was eligible for the cost-sharing waiver because the E/M led to a COVID-19 test.
Hence, following the CMS MLN Matters SE20011 guidance, the medical billing team appended the CS modifier to the E/M service’s claim line (but not the lab code).
Telehealth Visit Appeal
Consider another case that occurred during the pandemic, where a 32-year-old patient had a real-time audio-video telehealth visit because of a confirmed exposure to COVID-19. The reports stated sore throat and headache as the symptoms experienced by the patient.
Therefore, the healthcare provider performed an E/M service (e.g., CPT code 99214), leading to an order for COVID-19 testing.
Here, the billing team reported CPT code 99214-95-CS on the claim.
Why? Since the telehealth session for the E/M service led to a COVID-19 test, it qualified the procedure for the CS modifier (depending on payer requirements).
However, the claim was processed with patient coinsurance (e.g., 20%) instead of a full cost-sharing waiver. So, the billing team filed an appeal to recover the waived patient cost-sharing amount.
Note: Modifier CS waives patient cost-sharing (coinsurance/deductible), but it does not alter the reimbursement rate. Additionally, in the present day, several payers have discontinued or restricted the use of this modifier, so always review the current policy.
Preventing Previous Payment Take Back
Consider the case of a Medicare beneficiary who received coverage for services during the COVID-19 era.
The practice noticed that a service offered by the healthcare provider was covered 100%, but he did not provide the required documents to support the COVID-related procedure.
In such cases, the payer may issue a recoupment or take-back request to reclaim the reimbursement provided. However, the practice has the right to appeal this decision by providing ample documentation justifying the use of the CS modifier.
Conversely, if the modifier was not appended to a valid visit, auditing will help prevent financial loss and prove compliance.
Accurate Usage Guidelines for CS Modifier
Using the CS modifier without proper context can often result in denials and even trigger audits. Therefore, billing professionals should practice the following usage guidelines.
Append CS only to the E/M line
CMS guidance and AAPC state that the CS modifier applies to a qualifying E/M visit but not for the COVID-19 lab code or other non-related radiology services.
Justify Usage with Medical Record
If a claim is for COVID-19 testing, it must be justified with medical records. The medical record must clearly support that the E/M service was performed to evaluate the need for COVID-19 testing and resulted in an order for or performance of the test.
Do Not Charge for Cost-sharing
The FFCRA-era rules clearly instructed providers to avoid deductible collections, or coinsurance payments from Medicare beneficiaries for eligible services. However, this rule is valid if the CS modifier is properly applied.
Check the Payer’s Code List
Did you know that the CMS maintained specific code lists during the PHE? This included dedicated lists for:
- RHCs/FQHCs
- Physicians
- Hospital outpatient departments
Moreover, this code list also instructed that if any service code was appended with the modifier CS but was not on the list, its claim would be rejected or returned.
Quick Insight: These lists were primarily applicable during the PHE.
Ensure E/M Service Led to COVID-19 Test Order
As per the previous requirements, documentation must support the E/M service resulting in an order for or performance of a COVID-19 test. This supports the medical necessity and proper use of the CS modifier.
Final Thoughts on CS Modifier
The CS modifier has a unique dual history. It was originally introduced in the context of the 2010 Gulf oil spill and later repurposed during the COVID-19 Public Health Emergency to indicate cost-sharing waivers for testing-related services.
Following the end of the PHE in May 2023, routine use of modifier CS has largely been discontinued for Medicare claims and is now limited to:
- Legacy claims
- Audits
- Payer-specific policies
Therefore, billing teams must verify payer guidelines, ensure proper documentation, and confirm whether the modifier is still applicable before submitting claims.
For any doubts, reach out to the payer before submitting the claim or consider a specialized partner.
If you would rather not track every CMS update independently, NeuraBill’s medical billing and coding services keep the modifier application compliant and ready for audits.
