In ICD-10, acute lymphoblastic leukemia (ALL) is coded under C91.0, which sits in the C91 block for lymphoid leukemia. In the US clinical version (ICD-10-CM), that code is extended with a fifth character that records disease status: C91.00 for ALL not having achieved remission, C91.01 for ALL in remission, and C91.02 for ALL in relapse. This overview explains what those codes mean, how they connect to the disease itself, and why the right code matters to patients as well as to coders.
ALL is one of the hematologic malignancies, meaning a cancer of the blood-forming system. To code it well, you need to understand it well, so we will start with the disease and then work through the coding logic.
What Is Acute Lymphoblastic Leukemia?
ALL is a fast-growing cancer in which the bone marrow produces large numbers of immature lymphocytes called lymphoblasts. These blasts do not mature into working immune cells. Instead, they multiply and crowd out the normal cells that the marrow should be making.
The result is a shortage of healthy erythrocytes (red blood cells), platelets, and neutrophils. That shortage explains most early symptoms: anemia, infections, and a tendency toward bruising and bleeding problems.
ALL is divided by the type of lymphocyte involved. B-cell ALL is the more common form, while T-cell ALL is less common and more often presents with a mass in the chest. ALL is the most common childhood cancer, with a peak in early childhood, but it also occurs in adults, where it tends to be harder to cure.
The ICD-10 Codes for ALL Explained
The ICD-10 (International Classification of Diseases, 10th revision) is the World Health Organization’s system for classifying diagnoses. Many countries use the WHO version, which stops at C91.0. The US uses ICD-10-CM, which adds detail about remission status.
| Code | Description | Typical use |
|---|---|---|
| C91.0 | Acute lymphoblastic leukemia (WHO ICD-10 category) | International coding and mortality statistics |
| C91.00 | ALL not having achieved remission | New diagnosis, or disease still active during induction |
| C91.01 | ALL in remission | Patient in remission, including during maintenance therapy |
| C91.02 | ALL in relapse | Disease that has returned after a remission |
| Z85.6 | Personal history of leukemia | Treatment completed, no current disease or therapy |
The distinction between “in remission” and “personal history” trips up many coders. A patient who is still receiving treatment or surveillance for active disease control usually keeps a C91 code. Once treatment is finished and there is no evidence of disease, the history code generally applies. The treating hematologist’s documentation should make the status clear.
Why the code matters
Accurate coding feeds cancer registries, research databases, and insurance billing. A wrong remission status can distort outcome data and, for patients, can cause claim denials for expensive drugs or transfusions. In my practice, I ask that notes state the remission status in plain words so the code follows directly from the record.
Causes and Risk Factors
Most cases of ALL have no identifiable cause. The disease arises when a developing lymphocyte acquires genetic changes that let it grow without control and stop maturing. Known risk factors include:
- Inherited conditions such as Down syndrome, which carries a clearly increased risk
- High-dose radiation exposure
- Previous chemotherapy for another cancer
- Certain rare inherited syndromes affecting DNA repair
Having a risk factor does not mean a person will develop ALL, and most children and adults diagnosed with it have none of these factors.
Genetic changes inside the leukemia cells
ALL cells often carry chromosomal translocations, where pieces of two chromosomes swap places. The best known is the Philadelphia chromosome, t(9;22), which creates the BCR-ABL1 fusion gene. It is classically linked with chronic myeloid leukemia, but it is also found in ALL, especially in adults. Philadelphia-positive ALL is treated with tyrosine kinase inhibitors added to chemotherapy. These genetic findings do not change the ICD-10 code, but they strongly shape treatment and prognosis.
Symptoms and Diagnosis
ALL usually develops over days to weeks. Common symptoms include:
- Tiredness, pallor, and breathlessness from anemia
- Fevers and repeated infections
- Easy bruising, nosebleeds, or tiny red spots called petechiae
- Bone or joint pain, which in children can cause limping or refusal to walk
- Swollen lymph nodes, liver, or spleen
The first test is a complete blood count (CBC). It may show a high, normal, or low white cell count, often with anemia and low platelets. Blasts may be visible on the blood film.
The diagnosis is confirmed by bone marrow aspiration and biopsy. Under the WHO classification, a diagnosis of acute leukemia generally requires at least 20% blasts in the marrow. Flow cytometry identifies whether the blasts are B or T lineage, and cytogenetic and molecular tests look for changes such as the Philadelphia chromosome. A lumbar puncture checks whether leukemia has reached the fluid around the brain and spinal cord.
Treatment Phases and How Coding Follows Them
ALL treatment is long, often two to three years in total, and follows distinct phases. Each phase maps naturally onto a remission status in the code.
| Phase | Goal | Usual ICD-10-CM status |
|---|---|---|
| Induction | Clear blasts from the marrow and achieve remission | C91.00 until remission is documented |
| Consolidation / intensification | Destroy remaining leukemia cells | C91.01 once in remission |
| Maintenance | Lower-intensity therapy to prevent relapse | C91.01 |
| Relapse treatment | Regain remission after disease returns | C91.02 |
Treatment includes combination chemotherapy, therapy directed at the central nervous system, and targeted drugs for specific genetic subtypes. Supportive care, such as transfusions and antibiotics, is a large part of daily management.
Newer immunotherapies
For relapsed or refractory ALL, immunotherapy has changed the outlook. Options include antibody-based drugs that direct the patient’s T cells toward the leukemia and CAR T-cell therapy, in which a patient’s own T cells are engineered to recognize a marker on B-cell ALL. Stem cell transplant remains an option for higher-risk disease.
Key Takeaways
- ALL is coded under C91.0 in ICD-10; ICD-10-CM adds C91.00, C91.01, and C91.02 for active disease, remission, and relapse.
- Z85.6 applies once treatment is complete and there is no evidence of leukemia.
- ALL is a fast-growing cancer of immature lymphocytes that crowds out normal blood cells.
- Diagnosis rests on the blood count, bone marrow examination, flow cytometry, and genetic testing.
- Clear documentation of remission status is the key to correct coding.
For a broader view of leukemia types and treatment, see our leukemia guide.
Frequently Asked Questions
What is the ICD-10 code for acute lymphoblastic leukemia?
The WHO ICD-10 code is C91.0. In ICD-10-CM, used in the US, you choose C91.00 if the patient has not achieved remission, C91.01 if in remission, or C91.02 if in relapse.
Is B-cell ALL coded differently from T-cell ALL?
No. Both B-cell and T-cell ALL fall under the same C91.0 codes. The lineage is recorded in the pathology report and matters greatly for treatment, but it does not change the ICD-10 code.
When should C91.01 be changed to Z85.6?
C91.01 is used while the patient is in remission and still under active treatment or disease control. Once all treatment is complete and there is no evidence of leukemia, the personal history code Z85.6 is usually more appropriate. The treating physician’s documentation should guide the choice.
How is ALL different from acute myeloid leukemia in coding?
Acute myeloid leukemia sits in the myeloid leukemia block, most often coded as C92.0 (acute myeloblastic leukemia), because it arises from myeloid rather than lymphoid cells. The two diseases are treated differently, so correct lineage from the bone marrow report is essential for choosing the right code.
Can adults get acute lymphoblastic leukemia?
Yes. Although ALL is most common in young children, it also occurs in adults, and the risk rises again in older age. Adults are more likely to have the Philadelphia chromosome and generally have a harder course than children.
