Introduction: When to Seek Diagnostic Testing
People who notice certain worrying changes in their body should consider seeking medical evaluation for possible diffuse large B-cell lymphoma. The most common reason to visit a doctor is discovering a painless lump that doesn’t go away and seems to be growing larger. These lumps typically appear in the neck, armpits, or groin area, where lymph nodes are located just beneath the skin.[1]
You should especially contact a healthcare provider if you experience what doctors call “B symptoms” — a specific group of warning signs that include fever above 103 degrees Fahrenheit that lasts longer than two days or comes and goes without obvious cause, unexplained weight loss involving more than 10 percent of your body weight over six months, and heavy night sweats so intense they drench your sheets. About 30 percent of people with this type of lymphoma experience these B symptoms.[1][9]
Diffuse large B-cell lymphoma is considered a fast-growing cancer, which means symptoms can start or get worse in just a few weeks.[3] This rapid progression makes it important not to delay seeking medical attention when you notice persistent changes in your body that last for several weeks. Early diagnosis and treatment significantly improve outcomes, as this aggressive lymphoma is often treatable and curable, especially when caught early.[1]
Some people may develop lymphoma in areas outside the lymph nodes, which doctors call extranodal involvement. When this happens, symptoms depend on which organ or body part is affected. For example, lymphoma growing in the abdomen or bowel might cause pain, diarrhea, or bleeding. If it develops in the chest, you might experience breathlessness or a persistent cough.[3] Any combination of these symptoms warrants a visit to your general practitioner, who can then refer you for specialized testing if needed.
Diagnostic Methods for Identifying DLBCL
Physical Examination
The diagnostic process typically begins with a thorough physical examination. Your doctor will check for swollen lymph nodes in your neck, underarms, and groin by gently feeling these areas. They will also examine whether your spleen or liver is enlarged, as these organs can be affected by lymphoma.[8] During this examination, your healthcare provider will ask detailed questions about your symptoms, including when they started, how they’ve changed over time, and whether you’ve experienced fever, night sweats, or unintended weight loss.
The physical exam helps determine which areas of your body need further investigation. If your doctor finds enlarged lymph nodes or other concerning signs, they will order additional tests to determine whether lymphoma is present and, if so, what type it is.[6]
Blood Tests
Blood tests play multiple important roles in diagnosing diffuse large B-cell lymphoma. While they cannot definitively diagnose lymphoma on their own, they provide valuable information about your overall health and can sometimes show whether lymphoma cells are present in your bloodstream.[8]
A complete blood count evaluates involvement of the bone marrow, which may result in anemia (low red blood cells), thrombocytopenia (low platelets), or leukopenia (low white blood cells).[6] Your doctor will also check serum electrolyte levels because electrolyte abnormalities may occur when lymphoma affects the kidneys.
Lactate dehydrogenase (LDH) and uric acid levels are commonly measured because elevated levels correspond with the tumor burden — essentially, how much cancer is present in your body. Higher LDH levels often indicate more extensive disease.[6][8] Healthcare providers also test for viruses including Epstein-Barr virus, HIV, hepatitis B, and hepatitis C, as some types of lymphoma are associated with viral infections. Additionally, hepatitis B testing is performed in patients who will undergo combination treatment with rituximab, because this treatment carries a risk of viral reactivation.[6][8]
Lymph Node Biopsy
The main test to diagnose lymphoma is a lymph node biopsy, which involves removing part or all of a swollen lymph node so a specialist can examine it under a microscope.[3][8] This is the most definitive way to confirm whether you have diffuse large B-cell lymphoma and to distinguish it from other types of lymphoma or different diseases entirely.
Your healthcare provider may suggest removing lymph node tissue from other parts of the body depending on your symptoms and what imaging tests reveal. The sample collected during the biopsy is sent to a laboratory, where pathologists perform detailed examinations. They look at the appearance of the cells, their size and shape, and how they are spread out. The name “diffuse large B-cell lymphoma” actually comes from what pathologists see under the microscope: abnormal B cells that are larger than normal healthy B cells, spread out in a diffuse pattern rather than grouped together.[2]
In the laboratory, specialists also perform flow cytometry, which helps determine whether there is a clonal cell population present and helps differentiate between B-cell and T-cell origins.[6] Additional genetic studies identify specific genetic changes in the lymphoma cells, which are the most important identifiers of the exact subtype of DLBCL. Understanding your specific subtype helps your healthcare team predict how the cancer will likely progress and respond to treatment.[1]
Bone Marrow Testing
Bone marrow aspiration and biopsy are procedures used to collect cells from your bone marrow for testing. Bone marrow is the soft matter inside bones where blood cells are made. It has both a solid part and a liquid part. During bone marrow aspiration, a needle draws a sample of the fluid. During a bone marrow biopsy, a needle collects a small amount of the solid tissue.[8]
These samples are typically taken from the hip bone and sent to a laboratory for testing. The purpose is to check whether lymphoma cells have spread to your bone marrow. This information is important for determining the stage of your disease and planning appropriate treatment.[8]
Imaging Studies
Various imaging tests create pictures of the inside of your body, helping doctors see where lymphoma is located and how extensive it is. These tests are painless and non-invasive, though some require you to lie still for a period of time.
A PET-CT scan combines two imaging techniques. The PET (positron emission tomography) part uses a small amount of radioactive material to highlight areas where cells are very active, which often indicates cancer. The CT (computed tomography) part creates detailed cross-sectional images of your body. Together, these scans show both the location and the metabolic activity of lymphoma cells.[3]
PET-CT scans have greatly improved the accuracy of both staging (determining how far the cancer has spread) and restaging (checking whether treatment is working). In fact, findings on a PET scan at the end of therapy are considered the best predictors of a good treatment outcome.[17]
An MRI scan (magnetic resonance imaging) may be performed to look at your head or spine, particularly if there is concern that lymphoma might have affected your central nervous system.[3] MRI uses magnets, radio waves, and a computer to create detailed images of your body’s soft tissues without using radiation.[8]
For patients with gastrointestinal symptoms, upper and lower gastrointestinal imaging may be indicated, though these studies are not routinely required in staging DLBCL. Similarly, bone scans are performed for patients with bone pain or elevated alkaline phosphatase levels, which might indicate bone involvement.[6]
Lumbar Puncture
A lumbar puncture, also called a spinal tap, may be performed to check for lymphoma cells in the fluid that surrounds your brain and spinal cord. This test is particularly important for certain high-risk situations where the lymphoma might have spread to the central nervous system.[3]
During this procedure, a doctor inserts a thin needle between the bones of your lower spine to collect a small sample of cerebrospinal fluid. The sample is then examined in a laboratory to see if it contains any lymphoma cells. While the procedure might sound uncomfortable, it is generally well-tolerated and provides crucial information for treatment planning.
Diagnostics for Clinical Trial Qualification
Clinical trials are research studies that test new treatments or combinations of treatments for diffuse large B-cell lymphoma. To participate in a clinical trial, patients must meet specific criteria established by the researchers conducting the study. These criteria ensure patient safety and help researchers obtain meaningful results.
The standard tests used for clinical trial qualification are largely the same as those used for general diagnosis and staging of DLBCL. Most trials require confirmation of the diagnosis through tissue biopsy with pathological review. This means specialists must examine your biopsy sample and confirm that you have the specific type and subtype of lymphoma that the trial is studying.[8]
Clinical trials typically require recent imaging studies, particularly PET-CT scans, to document the extent of disease before treatment begins. These baseline scans are essential because they provide a starting point for measuring how well the experimental treatment works. Researchers compare scans taken during and after treatment to these baseline images to evaluate the treatment’s effectiveness.
Blood tests are standard requirements for clinical trial enrollment. Complete blood counts assess whether your bone marrow is functioning adequately and whether you have enough healthy blood cells to tolerate the proposed treatment. Tests of liver and kidney function are also essential because many cancer treatments are processed through these organs. If your liver or kidneys aren’t working well, you might not be able to safely participate in certain trials.[6]
Performance status evaluation is another critical component of clinical trial qualification. Researchers need to document how well you can perform daily activities and how much the lymphoma is affecting your life. This assessment helps determine whether you’re healthy enough for the experimental treatment and allows researchers to track changes in your quality of life throughout the study.[6]
Some clinical trials, particularly those testing treatments targeted at specific genetic abnormalities, require additional specialized testing. For example, trials investigating treatments for specific molecular subtypes of DLBCL may require genetic profiling of your lymphoma cells. This testing identifies particular genetic changes or markers that make your lymphoma more likely to respond to the experimental treatment being studied.



