Diagnosis Codes on NEMT Claims: Which ICD-10 Code Goes in Box 21

What the diagnosis code does on a ride claim

Box 21 of the CMS-1500, “Diagnosis or Nature of Illness or Injury,” holds the reason a service was given. HIPAA’s code set rule, 45 CFR 162.1002, has made ICD-10-CM the standard for diagnoses since October 1, 2015, and lists transportation among the services billed with HCPCS codes. The code set changes every October 1. The FY 2027 version runs from October 1, 2026 to September 30, 2027.

A ride company often does not know why the member is seeing the provider, so programs that want a code usually name one to use. Each is a real code with its own meaning in the FY 2027 code set:

• R69: “Illness, unspecified.”
• R68.89: “Other general symptoms and signs.”
• F99: “Mental disorder, not otherwise specified,” which Arizona names for a behavioral health ride.
• Z75.3: “Unavailability and inaccessibility of health-care facilities.”
• Z59.5: “Extreme poverty.”

Bill the one your payer names. The code also ties each service line to a reason: box 24E on every line holds the letter of the box 21 code it relates to. See the CMS-1500 for NEMT for the rest of the form.

Which diagnosis code each program wants

The form is the same everywhere, but the rule for box 21 is not. These are the fee-for-service rules, plus one Medicaid expansion plan, with the date of each source:

Program	Code to use	Rule
Indiana (module version 6.1, August 19, 2025)	R69 when the diagnosis is not known	Required on all claims. A claim without a valid code denies.
Texas Medical Transportation Program (handbook, September 2026)	Z753	Listed among the codes all MTP claims must use
Arizona (Chapter 14, revised July 31, 2026)	R68.89, or F99 for behavioral health, when unknown	At least one code. A blank ICD indicator gets the claim sent back.
Kansas (NEMT manual, updated March 2026)	R6889	Field 21, for dates of service from October 1, 2015
Nebraska (DHHS billing guidance, as of October 2026)	R69, with ICD indicator 0	Diagnosis pointer A on each line
New York (billing guidelines, version 2026-02, August 5, 2026)	R69 when nothing more specific is available	Required on electronic claims. Leave it blank on paper Form A.
North Dakota Medicaid Expansion (BCBSND, as of October 2026)	Z59.5	Named on its NEMT provider page for the diagnosis field
South Dakota (CMS-1500 instructions, updated January 2026)	No default named	Block 21 is mandatory, up to 12 codes
Medi-Cal (CMS-1500 completion, page updated August 2020)	None needed	Exempt when medical transportation is the only service on the claim

Idaho’s waiver non-medical transportation, a separate benefit for rides to everyday activities, uses R69 as the primary diagnosis in field 21 (handbook, March 30, 2026). Brokers and health plans follow their own claim instructions, so get them in writing before your first claim. For how a denial shows up on your remittance and how to fix it, see NEMT claim denials.

How to enter the code in box 21

The NUCC instruction manual (version 13, July 2025) sets the format, and state manuals repeat it:

1. Enter the ICD indicator. Put 0 for ICD-10-CM between the dotted lines in the upper right of box 21. Arizona returns a claim with this left blank.
2. Enter the code on line A. Left justified, with no decimal point, because the decimal is implied: R69, R6889, Z753.
3. Stop at 12 codes. Lines A to L hold up to 12. Medi-Cal accepts only two, and NUCC says no narrative description goes in the box.
4. Point each line to it. In box 24E of each service line, enter the letter, such as A, never the code itself.

In Texas, two parts of the Medicaid manual read differently. The Medical Transportation Program handbook (September 2026) lists Z753 in its row for box 24E as well as box 21. The general claims filing section (September 2026) says diagnosis codes go in box 21 only, never in 24E. So a Texas ride claim carries Z753 on line A of box 21 and the letter A in 24E.

On an electronic claim the same code travels in loop 2300 of the 837P, the HI segment, which New York names as 2300 HI01-2. The place of service code is a separate box with its own rule. See place of service codes.

Z75.3 and Z59.82: what the transportation codes mean

Z75.3 sits in category Z75, “Problems related to medical facilities and other health care.” Its title covers health care facilities that are unavailable or out of the patient’s reach, and Texas uses it on every ride claim.

Z59.82, “Transportation insecurity,” is newer. It is not in the code set for the year that ended September 30, 2022, and it appears from October 1, 2022, in category Z59, “Problems related to housing and economic circumstances.” Since the April 1, 2023 update, the code book notes Z75.3 under it as a separate condition, not part of Z59.82. North Dakota’s expansion plan names Z59.5, “Extreme poverty,” from the same category.

The FY 2027 coding guidelines place category Z59 among the social determinants of health codes: codes for social problems, conditions, or risk factors that influence a patient’s health. They are assigned from documentation in the patient’s medical record, which can include notes from social workers, case managers, or nurses, and from information the patient reports once a clinician signs off on it. When a clinic codes Z59.82, it records that the patient lacks reliable transportation. The code describes the patient’s situation, not a service, and it does not make a ride covered or raise its pay. Coverage comes from the state’s NEMT rules under the Medicaid assurance of transportation and the trip’s authorization. Put Z59.82 on a claim only if your payer names it.

Diagnoses on authorizations, and keeping them private

Some programs care more about the diagnosis before the ride than on the claim:

• Arizona. A prior authorization request for NEMT must contain a valid diagnosis code if known, with R68.89 or F99 when it is not (Chapter 14, revised July 31, 2026).
• Medi-Cal. A wheelchair or litter van ride needs a treatment authorization request with a prescription that gives the purpose, the frequency or dates, and the condition that makes ordinary transportation inadvisable. For ongoing rides, a diagnosis alone, such as “multiple sclerosis” or “stroke,” is not enough without the chronic nature of the condition and a treatment plan (pages updated August 2020). See NEMT medical necessity forms.

A real diagnosis is sensitive. Federal rule 42 CFR 431.305 lists medical data, including diagnosis, among the information every state Medicaid agency must safeguard. For a NEMT company covered by HIPAA it is protected health information, and HIPAA’s minimum necessary standard, 45 CFR 164.502(b), asks you to limit what you use, share, or request to what the task needs. Use your program’s default code when you do not know the diagnosis, share a real one only with the staff who need it to bill, and never ask a rider for one just to fill box 21.