Leukemia is a type of blood cancer that begins in the bone marrow, where blood cells are made. There are several different types of leukemia, but they all involve the abnormal and uncontrolled production of immature white blood cells, called leukemic blasts or leukemia cells.
In most cases, leukemia will cause abnormalities that can be detected on routine blood work. This is because the abnormal leukemia cells disrupt normal blood cell production, leading to irregular blood cell counts. Additionally, the presence of blast cells or other abnormal cells in the blood can indicate leukemia.
Complete Blood Count
A complete blood count (CBC) is a common blood test that provides information about the different types of cells in the blood. It measures the number of red blood cells, white blood cells, and platelets. It also calculates the percentage of each type of white blood cell.
In leukemia, the CBC typically shows:
- High white blood cell count
- Low red blood cell count (anemia)
- Low platelet count (thrombocytopenia)
- Abnormal white blood cell differential with blasts or abnormal cell types
These abnormalities occur because the leukemia cells crowd out the normal blood cell development in the bone marrow. However, some types of leukemia, like chronic lymphocytic leukemia, can present with a normal or low white blood cell count initially.
White Blood Cell Count
A high white blood cell count is one of the most common signs of leukemia on a CBC. In acute leukemias, the number of white blood cells is usually very elevated. Counts over 100,000 per microliter are common.
In chronic leukemias like chronic myeloid leukemia (CML), the white count is variably elevated. CML counts may range from normal to over 100,000 per microliter.
Red Blood Cell Count
Most types of leukemia cause a decrease in the number of red blood cells, known as anemia. This occurs because the rapid growth of leukemia cells suppresses the normal production of red blood cells.
Red blood cell counts below the normal range help diagnose leukemia and indicate that a patient may experience fatigue, weakness, shortness of breath or other symptoms of anemia.
Platelet Count
Thrombocytopenia, or a low platelet count, is common in acute leukemias. Platelets are essential for normal blood clotting, so very low platelet counts (under 10,000 per microliter) can lead to serious bleeding issues.
Chronic leukemias like CML do not always affect the platelet count. But over time, the platelet count may drop as the leukemia worsens.
White Blood Cell Differential
The white blood cell differential examines the different types of white blood cells. It normally shows a percentage of neutrophils, lymphocytes, monocytes, eosinophils and basophils.
In leukemia, blast cells or abnormal cells will be visible on the differential. The presence of over 5% blast cells is diagnostic of acute leukemia.
The type of abnormal cells present helps classify the specific leukemia subtype. For example, CML shows very high neutrophils and metamyelocytes on the differential.
Peripheral Blood Smear
The peripheral blood smear is a slide made from a drop of blood and examined under the microscope. This test gives information about the shape and appearance of the blood cells.
In leukemia, the peripheral smear shows abnormal, immature blast cells. The quantity and appearance of the blasts can help diagnose the leukemia type and monitor the disease over time.
Some findings on the blood smear in leukemia include:
- Increased blast cells
- Abnormally shaped cells
- Immature blood cells
- Decreased platelets
- Abnormal white blood cell morphology
The blood smear provides a more detailed look than the CBC differential and can pick up subtle abnormalities that point to leukemia.
Flow Cytometry
Flow cytometry is a test that measures specific cell markers on the surface of blood cells. It can identify the cell type and maturity of cells based on their biomarker patterns.
In leukemia, flow cytometry is used to detect abnormal, immature cells with leukemia markers. It can help diagnose leukemia and determine the specific subtype, such as acute myeloid leukemia vs acute lymphoblastic leukemia.
Flow cytometry provides more definitive information than a visual examination of the blood smear. It is an important part of leukemia diagnosis and classification.
Bone Marrow Biopsy
While the above blood tests can suggest leukemia, examining the actual bone marrow provides the most definitive diagnosis. This is done by bone marrow biopsy and aspiration.
A sample of bone marrow is taken from the hip bone and examined under the microscope. In leukemia, the bone marrow shows infiltration with blast cells – usually over 20-30% – that have blocked normal marrow function.
The findings of the bone marrow analysis confirm the leukemia diagnosis and provide information needed to plan appropriate treatment.
Genetic Tests
Specialized genetic tests are often performed in leukemia patients to detect chromosomal abnormalities or genetic mutations related to the disease. These include:
- Cytogenetics – analyzes chromosomes of leukemia cells for translocations, deletions, extra or missing chromosomes
- FISH – fluorescent in situ hybridization detects specific genetic abnormalities
- PCR – polymerase chain reaction amplifies DNA to detect mutated genes
- Next-generation sequencing – provides complete genetic profile of leukemia cells
Identifying the genetic mutations involved in each patient’s leukemia helps determine prognosis and guide treatment using targeted therapies.
Summary of How Leukemia Shows Up on Blood Work
In summary, the common findings indicating leukemia on blood tests include:
| Blood Test | Leukemia Findings |
|---|---|
| Complete blood count | High white blood cell count, low red blood cell and platelet counts, blast cells on differential |
| Peripheral blood smear | Presence of abnormal, immature blast cells |
| Flow cytometry | Leukemic blast cells with abnormal marker patterns |
| Bone marrow biopsy | Blast cells replacing normal marrow cells |
| Genetic tests | Specific chromosomal and genetic abnormalities |
While some types of leukemia may present with subtle blood test changes at first, nearly all leukemias will demonstrate abnormalities as the disease progresses or with more advanced testing.
The blood work findings seen in leukemia are generally different from what is expected with infections or other conditions. However, the results must always be interpreted in the full clinical context for each patient.
Questions the Blood Work May Help Answer
Some key questions that doctors use blood test results to help answer include:
Does the patient have leukemia?
Findings like elevated white blood cell counts with blasts on the differential provide strong evidence for acute leukemias. Chronic leukemias can be harder to diagnose definitively from blood work alone.
What type of leukemia does the patient have?
The specific pattern of blood cell abnormalities and genetics can classify the leukemia as acute/chronic and myeloid/lymphoid leukemia subtypes.
What is the severity of the leukemia?
Higher blast percentages and blood cell count extremes usually indicate more advanced, aggressive leukemia.
How well is treatment working?
Blood counts and blast percentages improving demonstrate treatment response. Blood work is monitored regularly during leukemia treatment.
Has the leukemia relapsed?
Rising blast cells or worsening blood counts after treatment may signify relapse.
What Else Can Mimic Leukemia Blood Findings?
While certain blood test results are highly suggestive of leukemia, other conditions can sometimes mimic these findings. Examples include:
- Infection – particularly viral infections like mononucleosis (mono)
- Bone marrow suppression from chemotherapy
- Aplastic anemia – bone marrow failure from autoimmune disorders or toxins
- Myelodysplastic syndromes – marrow problems leading to low blood counts
- Autoimmune disorders
- Rare blood disorders like marginal zone lymphoma
For this reason, blood test results indicating leukemia always require correlation with the patient’s clinical scenario. Additional testing like bone marrow evaluation may be needed to reach a definitive diagnosis.
Conclusion
Leukemia will cause abnormalities on routine blood work like the complete blood count in most cases. Elevated white blood cell counts with abnormal blast cells are common findings. Anemia and low platelets also frequently occur.
While blood tests cannot make a definite leukemia diagnosis by themselves, they provide the first clues pointing toward leukemia. This prompts further testing like blood smears, bone marrow studies and genetic tests to confirm that leukemia is present.
Ongoing blood work is essential for classifying leukemia, gauging severity, and monitoring response to treatment. Doctors use blood test results in conjunction with other clinical information to guide the care of leukemia patients.