Medicare pays for a CBC with differential only when the claim carries an ICD-10 diagnosis code that appears on the approved list under National Coverage Determination 190.15. The procedure code is almost always CPT 85025, but the diagnosis code is what decides whether the claim is paid or denied. Codes tied to a documented blood disorder, a related medical condition, or a sign or symptom that justifies the workup will generally support coverage. Codes that describe a routine exam or an unrelated condition will not.
Covered Diagnosis Categories Under NCD 190.15
NCD 190.15 is the national policy that governs blood count coverage. It doesn’t publish a single flat list of every acceptable ICD-10 code. It defines the clinical categories in which a blood count is considered reasonable and necessary, and the covered codes flow from those categories.
The NCD recognizes blood counts for evaluating and diagnosing diseases involving abnormalities of the blood or bone marrow. The primary disorders it names are anemia, leukemia, polycythemia, thrombocytosis, and thrombocytopenia. It also covers conditions that secondarily affect the blood, including infections, inflammation, coagulopathies, neoplasms, and toxic substance exposure. Blood counts ordered to monitor the effects of treatment on the blood or bone marrow are covered as well.1Centers for Medicare & Medicaid Services. NCD – Blood Counts (190.15)
In practice, the ICD-10 codes that commonly support a CBC claim fall into several groups.
- Blood disorders: Iron deficiency anemia (D50.9), unspecified anemia (D64.9), thrombocytopenia (D69.6), and other diagnoses in the D50–D89 range.
- Neoplasms: Any active cancer diagnosis, especially when the patient is receiving chemotherapy or radiation that suppresses bone marrow function.
- Infections and inflammation: Sepsis, pneumonia, urinary tract infections, and similar conditions where white blood cell counts guide diagnosis and treatment.
- Chronic disease monitoring: Chronic kidney disease (N18 codes), liver disease, and other conditions where long-term drug therapy requires periodic blood counts to track medication effects.
- Signs and symptoms before a definitive diagnosis: Fatigue (R53.83), fever of unknown origin (R50.9), unexplained weight loss (R63.4), and abdominal pain (R10 codes), among other symptoms that justify an initial diagnostic workup.
Local Coverage Determinations issued by regional Medicare Administrative Contractors can add or narrow these rules for a specific jurisdiction, so a diagnosis accepted in one state may be scrutinized differently in another. You can look up the LCD that applies to your area by searching the CMS Medicare Coverage Database by CPT code and selecting your state.2Centers for Medicare & Medicaid Services. MCD Search
ICD-10 Codes That Will Get the Claim Denied
Certain ICD-10 codes are flagged as non-covered for all laboratory NCDs, including blood counts. These represent routine encounters or administrative purposes rather than the diagnosis or treatment of a medical condition. The CMS NCD Coding Policy Manual identifies them.3Centers for Medicare & Medicaid Services. Medicare National Coverage Determinations (NCD) Coding Policy Manual and Change Report (ICD-10-CM)
- Z00.00 and Z00.01: general adult medical examination, with or without abnormal findings
- Z00.110 and Z00.111: newborn health examinations
- Z00.129: routine child health examination without abnormal findings
- Z02.1: pre-employment examination
Beyond those universal exclusions, NCD 190.15 maintains its own list of codes that don’t support medical necessity for a blood count specifically. These include conditions with no clinical connection to blood cell parameters, such as plantar warts (B07.0) and anogenital warts (A63.0). The full list runs to hundreds of codes. When a diagnosis isn’t clearly on the covered side, check the NCD Coding Policy Manual or the applicable LCD billing article for your region before the claim goes out.
Specificity Matters as Much as the Code Category
The guiding principle in coding a CBC is specificity. Always use the most precise ICD-10 code the patient’s chart supports. Coding D64.9 (unspecified anemia) when the record documents iron deficiency anemia invites scrutiny and can trigger a denial, because Medicare expects the code on the claim to match the documentation in the note.
The diagnosis should appear in the note for the encounter that triggered the order, not merely on the patient’s general problem list. An ICD-10 code sitting on a claim form with nothing in the progress note to back it up is the scenario that generates audit recoveries in Medicare’s Comprehensive Error Rate Testing program.4CMS. Complying with Documentation Requirements for Lab Services
The Annual Physical Trap
One of the most common billing mistakes is coding a CBC as part of a routine physical or wellness visit without a supporting diagnosis. Federal regulations exclude routine checkups and examinations performed for purposes other than diagnosing or treating a specific illness, symptom, or injury. The regulation carves out exceptions for specific preventive services like mammography, colorectal cancer screening, and diabetes screening, but a CBC is not on that list.5eCFR. 42 CFR 411.15 – Particular Services Excluded From Coverage
A physician can still order a CBC during a wellness visit if the patient has a documented sign or symptom that justifies it. The difference is in the coding. A patient who mentions persistent fatigue during an annual wellness visit can have a CBC billed under R53.83 (fatigue), and that claim has a real chance. The same CBC billed under Z00.00 (routine exam) will be denied. The diagnosis code has to point to a medical problem, not the visit type.
Frequency Limits Can Deny a Covered Code
Even when the diagnosis code is on the approved list, testing too often for that condition can still result in a denial. NCD 190.15 states that repeat testing may not be indicated unless abnormal results are found or the patient’s clinical condition changes. The exception is patients with conditions that carry an ongoing risk of developing blood abnormalities, where periodic monitoring is justified even when prior results were normal.1Centers for Medicare & Medicaid Services. NCD – Blood Counts (190.15)
LCDs often add more specific frequency expectations. A patient on stable chemotherapy might have a CBC covered weekly, while a patient with well-controlled anemia might justify testing only every few months. When a claim exceeds the frequency the policy contemplates, it can be denied as not reasonable and necessary unless the provider submits documentation showing why more frequent testing was warranted.
Documentation That Backs the Code Up
The most common reason lab claims are flagged as improper is insufficient documentation, not the wrong code. The chart needs to support two things: that the physician intended to order the test, and that there was a medical reason to order it.
Intent to order means a signed progress note, signed office visit note, or signed physician order in the record. An unsigned requisition by itself does not count, and CMS will not accept an after-the-fact attestation statement to fix a missing signature on a requisition or physician order. If the test was ordered by phone, both the ordering provider’s office and the testing facility need to document the call in the patient’s record.
Medical necessity documentation means the chart contains the clinical findings, symptoms, or condition that connect to the ICD-10 code on the claim. If the code says iron deficiency anemia, the note needs to reflect the workup or the established diagnosis behind that code.
What to Do When a Claim Is Denied
A denied CBC claim isn’t necessarily the end of the road. The first level of appeal is a redetermination, a review by MAC personnel who were not involved in the original decision. Either the provider or the beneficiary can request one by submitting a written request within 120 days of receiving the denial notice. The MAC generally issues a decision within 60 days.6Centers for Medicare & Medicaid Services. First Level of Appeal: Redetermination by a Medicare Contractor
The request should include the beneficiary’s name and Medicare number, the specific dates and services at issue, and an explanation of why the denial was wrong. If the chart clearly supports medical necessity and the ICD-10 code is on the covered list, the denial may have been a processing error or a missing piece of paperwork that can be corrected on redetermination. If the coding was the problem, that is where a more specific or better-supported diagnosis code, drawn from the clinical documentation that already exists in the record, can turn the denial around.