Introduction: Who Should Undergo Diagnostics and When

Hairy cell leukaemia is an uncommon type of blood cancer that develops gradually over time. Because the disease progresses slowly, many people don’t experience symptoms in the early stages. Sometimes, a healthcare provider discovers it accidentally during a routine blood test performed for a completely different reason.^[1] This makes understanding when to seek diagnostic testing particularly important.

You should consider seeing your doctor if you experience persistent tiredness that doesn’t improve with rest, or if you notice you’re getting infections more frequently than usual. Other warning signs include easy bruising or bleeding, shortness of breath during everyday activities, or unexplained weight loss.^[3] Some people also feel pain or fullness below their ribs, particularly on the left side, which may indicate an enlarged spleen pressing against the stomach.^[4]

If you develop any combination of these symptoms, it’s advisable to schedule an appointment with your general practitioner. They will ask about your medical history and perform a physical examination. During this exam, your doctor may gently press on your abdomen to check if your spleen or liver feels larger than normal. An enlarged spleen is found in more than ninety percent of patients with hairy cell leukaemia, though this finding has become less common in recent years as blood tests now catch the disease earlier.^[2]

Your age and gender may also influence when diagnostics are recommended. This condition typically affects people between the ages of forty and seventy, with the average age at diagnosis being around fifty-five to fifty-eight years old. Men are affected about four times more often than women.^[6] However, anyone experiencing concerning symptoms should seek medical advice regardless of their demographic profile.

Classic Diagnostic Methods

Diagnosing hairy cell leukaemia involves several steps, starting with simple tests and progressing to more specialized procedures when needed. The diagnostic journey typically begins with a careful physical examination and medical history review, followed by blood tests that provide the first clues about what might be happening in your body.

Physical Examination

Your healthcare provider will conduct a thorough physical examination, paying special attention to certain areas of your body. They will gently feel your abdomen, checking for signs of an enlarged spleen or liver. The spleen is located on the left side of your upper abdomen, and when it swells, you might feel fullness in your belly or discomfort when eating.^[11] Your doctor will also check your lymph nodes in the neck, underarms, and groin area, though swollen lymph nodes are less common in hairy cell leukaemia compared to other types of cancer.^[2]

Complete Blood Count (CBC) with Differential

A complete blood count is usually the first laboratory test your doctor will order. This test measures the levels of different types of cells in your blood, including red blood cells, white blood cells, and platelets (small cells that help your blood clot).^[3] In hairy cell leukaemia, this test typically shows low numbers of all three types of blood cells, a condition called pancytopenia. The test may also reveal a reduction or complete absence of a specific type of white blood cell called monocytes, which is a particularly telling sign.^[2]

Low red blood cell counts explain why you might feel tired all the time, a condition called anemia. Low white blood cell counts make you more susceptible to infections. Low platelet counts lead to easy bruising and bleeding problems, such as frequent nosebleeds or bleeding gums.^[4] These blood abnormalities develop because the leukaemia cells crowd the bone marrow, leaving less room for healthy blood cells to grow.

Peripheral Blood Smear

When blood test results raise concerns, the next step is often a peripheral blood smear. In this test, laboratory specialists place a drop of your blood on a glass slide and examine it under a microscope. They look for abnormal cells that have a distinctive appearance.^[2] The leukaemia cells in hairy cell leukaemia have a pale center and tiny projections extending from their surface, making them look “hairy” under magnification. This is where the disease gets its name.

However, these hairy cells might not always be visible in the blood sample, especially in early stages of the disease. Sometimes the abnormal cells remain primarily in the bone marrow and haven’t yet spilled over into the bloodstream in large numbers. If hairy cells aren’t seen in the blood, this doesn’t rule out the diagnosis—further testing is needed.^[2]

Bone Marrow Biopsy

A bone marrow biopsy is considered the most reliable method for diagnosing hairy cell leukaemia. During this procedure, your doctor uses a thin, hollow needle to remove small samples of bone marrow, usually from the back of your hip bone.^[11] The bone marrow is the soft, spongy tissue inside bones where blood cells are made. This test allows specialists to see if hairy cells have infiltrated the bone marrow.

In hairy cell leukaemia, the bone marrow often becomes fibrotic, meaning it develops excess fibrous tissue that makes it harder to draw out a sample. This is why the procedure sometimes requires more effort from the healthcare provider.^[6] You can ask your doctor to order pain relief medication and anti-anxiety medication before the procedure if you feel nervous or uncomfortable about having it done.

The bone marrow sample is examined under a microscope to look for the characteristic hairy cells and to assess how much of the marrow has been affected by leukaemia. Pathologists also check for fibrosis and other changes in the bone marrow structure that help confirm the diagnosis.

Immunophenotyping and Flow Cytometry

Immunophenotyping is a sophisticated test that identifies cells based on specific markers, called clusters of differentiation or CD markers, found on their surface. These markers are like identification badges that tell us what type of cell we’re looking at.^[2] In hairy cell leukaemia, the abnormal cells display a unique pattern of markers that helps distinguish them from other types of leukaemia or lymphoma.

The test uses special antibodies that attach to specific markers on the cell surface. In classic hairy cell leukaemia, the cells test positive for several markers including CD19, CD20 (at very high levels), CD11c, CD25, CD103, CD123, and CD200.^[2] This particular combination of markers is characteristic of hairy cell leukaemia and helps doctors differentiate it from other blood cancers that might look similar under a microscope.

Flow cytometry is the technique used to perform immunophenotyping. It allows laboratory specialists to analyze thousands of cells quickly and accurately. Although a bone marrow biopsy might be required to enroll in a clinical trial, the diagnosis of hairy cell leukaemia can usually be made through flow cytometry alone, without necessarily needing a bone marrow sample.^[17]

Genetic Testing: BRAF Mutation

Most people with hairy cell leukaemia—approximately ninety to ninety-five percent—have a specific change in their genetic material called the V600E BRAF mutation.^[4] The BRAF gene normally helps control cell growth, but when this mutation occurs, cells divide and survive without proper control, leading to cancer. This genetic change happens after you’re born; it’s not inherited from your parents.

Testing for the BRAF mutation can help confirm the diagnosis of hairy cell leukaemia and distinguish it from other similar conditions. This test has become an important diagnostic tool because it’s highly specific to hairy cell leukaemia. The mutation can be detected through blood samples or bone marrow samples, providing a genetic fingerprint that aids in accurate diagnosis.^[17]

Imaging Tests

Imaging studies help doctors see inside your body without surgery. A computed tomography scan (CT scan) or abdominal ultrasound may be ordered to evaluate the size of your spleen, liver, and lymph nodes.^[4] These tests create detailed pictures that show whether organs are enlarged or if there are tumors present. While imaging doesn’t diagnose hairy cell leukaemia on its own, it provides important information about how the disease has affected different parts of your body and helps with treatment planning.

Distinguishing Hairy Cell Leukaemia from Other Conditions

Several other blood disorders can resemble hairy cell leukaemia, so doctors must carefully rule out these alternatives. One important condition to distinguish is hairy cell leukaemia variant (HCL-V), which is actually a separate disease despite having a similar name. This variant behaves more aggressively and responds differently to treatment.^[1]

Hairy cell leukaemia variant can be identified through immunophenotyping because the cells lack certain markers (CD25 and CD123) that are present in classic hairy cell leukaemia. Additionally, people with the variant form typically have a high white blood cell count, while those with classic hairy cell leukaemia usually have low counts.^[17] The variant form also doesn’t have the BRAF mutation that is characteristic of classic hairy cell leukaemia.

Other conditions that need to be distinguished include splenic marginal zone lymphoma and other B-cell lymphoproliferative disorders. These are different types of blood cancers that affect similar cells but require different treatments.^[6] Your healthcare team will use the combination of physical findings, blood tests, bone marrow examination, immunophenotyping, and genetic testing to accurately identify which condition you have.

Diagnostics for Clinical Trial Qualification

Clinical trials are research studies that test new ways to prevent, diagnose, or treat diseases. If you’re considering participating in a clinical trial for hairy cell leukaemia, you’ll need to undergo specific diagnostic tests to determine if you’re eligible. These tests serve two purposes: they confirm your diagnosis with certainty, and they establish baseline measurements that researchers will use to track how well the experimental treatment works.

Standard Diagnostic Criteria

Most clinical trials require participants to have a confirmed diagnosis of hairy cell leukaemia through multiple methods. This typically includes having a bone marrow biopsy that shows the presence of hairy cells, even though the diagnosis might be possible without it in regular clinical practice.^[17] The bone marrow biopsy provides detailed information about the extent of disease in your marrow and serves as a baseline for comparison during and after treatment.

Immunophenotyping through flow cytometry is essential for clinical trial enrollment. Researchers need to document that your leukaemia cells display the characteristic pattern of surface markers (such as being positive for CD19, CD20, CD11c, CD25, CD103, and CD123) that define classic hairy cell leukaemia.^[2] This ensures that all participants in the trial have the same type of disease, which makes the research results more reliable and meaningful.

Measurable Residual Disease Testing

Measurable residual disease (MRD) testing looks for very small numbers of leukaemia cells that might remain in your body even when all visible signs of disease have disappeared. This sophisticated testing can detect one leukaemia cell among thousands or even millions of normal cells. For clinical trials, MRD testing is increasingly important because it helps researchers understand how deeply a treatment works.^[17]

MRD testing can be done by looking for the BRAF mutation that’s present in most hairy cell leukaemia cases, or by searching for a unique genetic signature called immunoglobulin heavy chain gene rearrangement that’s specific to each person’s leukaemia cells. These tests are typically performed on bone marrow samples. While MRD testing provides valuable information for research purposes, it’s still unclear whether doctors should change treatment decisions based on MRD results, so this remains an active area of investigation.^[17]

Blood Count Requirements

Clinical trials often have specific requirements about your blood cell counts before you can enroll. For example, trials might require that you have low numbers of certain blood cells (such as hemoglobin less than ten grams per deciliter, or platelets less than one hundred thousand per microliter) to demonstrate that you need treatment.^[6] Alternatively, some trials might require that your blood counts be within certain ranges to ensure you can safely tolerate the experimental treatment.

These blood count criteria help ensure that everyone in the trial is at a similar stage of disease. This makes it easier for researchers to determine whether differences in outcomes are due to the treatment being tested rather than differences in how advanced each person’s disease was at the start of the study.

Assessment of Disease Burden

Clinical trials need to measure how much disease is present in your body at the beginning of the study. This is called assessing your disease burden. Doctors evaluate this through several measurements: the percentage of hairy cells in your bone marrow, the size of your spleen (measured by physical examination or imaging), and sometimes the presence of enlarged lymph nodes in your abdomen detected by CT scans.^[2]

Some clinical trials specifically look at certain features that might predict how well a treatment will work. These prognostic features can include your age, your hemoglobin level, your platelet count, your neutrophil count (a type of white blood cell), whether you have enlarged lymph nodes, and whether your spleen is massively enlarged.^[6] Understanding these factors helps researchers determine which patients might benefit most from a particular treatment approach.

Additional Laboratory Tests

Beyond tests that directly examine leukaemia cells, clinical trials typically require various laboratory tests to assess your overall health. These include kidney function tests, liver function tests, and tests for viral infections such as hepatitis B, hepatitis C, or HIV. Some experimental treatments can’t be used safely in people with certain underlying health conditions, so these tests help protect your safety.^[2]

You might also undergo additional genetic or molecular tests that aren’t part of standard clinical care but are needed for research purposes. For example, researchers might want to analyze multiple genes beyond just BRAF to understand more about how hairy cell leukaemia develops and responds to treatment. These extra tests don’t usually change your treatment but contribute to scientific knowledge that could help future patients.

Imaging Requirements

Some clinical trials require baseline CT scans or other imaging studies even if you haven’t had symptoms that would normally prompt these tests in regular clinical practice. The images provide objective measurements of organ sizes and the presence of any masses, which can be compared to images taken later to see if the treatment is working. While imaging isn’t always necessary for diagnosis in routine care, it provides standardized information that’s valuable for research studies.