Non-Hodgkin’s lymphoma is diagnosed through a combination of physical examination, blood tests, imaging scans, and most critically, a biopsy of affected tissue. No single test confirms the diagnosis on its own. Instead, doctors build a picture step by step, starting with blood work and imaging to identify suspicious areas, then taking a tissue sample to confirm cancer cells under a microscope, and finally running specialized lab tests to determine the exact subtype and stage.
Initial Signs That Prompt Testing
The diagnostic process usually begins when someone notices a painlessly swollen lymph node in the neck, armpit, or groin, or when a doctor finds one during a routine exam. Other symptoms that raise suspicion include persistent fatigue, unexplained weight loss, drenching night sweats, and fevers without an obvious infection. These last three are collectively called “B symptoms,” and their presence helps doctors gauge severity later in the process.
A physical exam focuses on lymph node groups throughout the body and checks for an enlarged spleen or liver. From there, the workup moves to blood tests and imaging.
What Blood Tests Reveal
Blood tests alone can’t confirm non-Hodgkin’s lymphoma, but they provide important clues and help rule out other conditions. A complete blood count shows whether your white blood cells, red blood cells, or platelets are at abnormal levels. Doctors also measure a protein called lactate dehydrogenase (LDH), which is often elevated in people with lymphoma because rapidly dividing cancer cells release it into the bloodstream. Higher LDH levels can signal more aggressive disease.
Blood work also screens for viruses like HIV, hepatitis B, and hepatitis C. These infections don’t just increase the risk of developing lymphoma; they directly affect which treatments are safe to use. If lymphoma cells are circulating in the blood, specialized testing can sometimes detect them at this stage, though that’s more common in certain subtypes like mantle cell lymphoma.
Imaging Scans and What They Show
Imaging gives doctors a map of where the disease is in your body. The most informative tool is a PET-CT scan, which combines two technologies: a CT scan that shows detailed anatomy and a PET scan that highlights areas of unusually high metabolic activity, a hallmark of cancer cells. PET-CT can identify disease in lymph nodes, organs, and other tissues that a CT scan alone might miss. It’s particularly useful for spotting extranodal involvement, meaning lymphoma that has spread beyond the lymph nodes into places like the stomach, lungs, or bones.
MRI scans are sometimes used when doctors need a closer look at specific areas, particularly the brain or spinal cord. The imaging results guide where biopsies should be taken and are essential for determining the stage of the disease later.
Biopsy: The Test That Confirms the Diagnosis
A biopsy is the only way to definitively diagnose non-Hodgkin’s lymphoma. This involves removing all or part of a suspicious lymph node so a pathologist can examine it under a microscope. The preferred method is a surgical excision, where an entire lymph node is removed. This approach provides a definitive diagnosis in about 98% of cases.
A less invasive alternative is a core needle biopsy, which uses a hollow needle to extract a cylinder of tissue. While this reaches a definitive diagnosis in roughly 92% of cases, it carries a higher risk of inconclusive or inaccurate results. A large French study found that when pathologists reviewed core needle biopsies, the rate of disagreement between initial and expert diagnoses was notably higher than with excisional biopsies. The smaller tissue sample simply makes it harder to evaluate the architecture of the lymph node, which is critical for distinguishing between lymphoma subtypes. When a needle biopsy comes back unclear, a surgical excision is typically the next step.
If lymphoma is suspected in areas outside the lymph nodes, biopsies can be taken from other tissues, including the skin, stomach, or other organs where the imaging showed abnormalities.
How the Subtype Is Determined
There are more than 60 subtypes of non-Hodgkin’s lymphoma, and identifying the exact one matters enormously for treatment. Once the biopsy tissue reaches the lab, it goes through several rounds of specialized testing.
Immunophenotyping
This technique uses flow cytometry to identify specific proteins on the surface of the lymphoma cells. By checking for markers like CD19 and CD20 (found on B cells) or CD3 (found on T cells), pathologists can determine whether the lymphoma originates from B cells or T cells. About 85% of non-Hodgkin’s lymphomas are B-cell types. Additional markers like CD5, CD10, and CD23 help narrow it further. For example, a B-cell lymphoma that is positive for both CD5 and CD23 points toward chronic lymphocytic leukemia/small lymphocytic lymphoma, while CD10 positivity suggests follicular lymphoma.
Genetic and Chromosomal Testing
Many lymphoma subtypes carry signature genetic changes, and a test called FISH (fluorescence in situ hybridization) can detect them. FISH works by attaching fluorescent probes to specific chromosomes in the cancer cells and examining them under a specialized microscope. It’s sensitive enough to pick up low-level genetic abnormalities that standard chromosome analysis might miss.
Certain chromosomal rearrangements are strongly tied to specific subtypes. About 80% of follicular lymphomas carry a translocation between chromosomes 14 and 18, which causes overproduction of a protein that helps cancer cells resist normal cell death. Burkitt lymphoma, a fast-growing subtype, is characterized by a different rearrangement involving chromosome 8 and 14. Diffuse large B-cell lymphoma, the most common subtype overall, shows the chromosome 14/18 translocation in 20 to 30% of cases. These genetic fingerprints not only confirm the diagnosis but also influence prognosis and treatment decisions.
Staging With the Lugano Classification
Once the subtype is confirmed, doctors determine how far the disease has spread using the Lugano classification system, which has four stages:
- Stage I: Lymphoma is in one lymph node group or one area outside the lymph nodes.
- Stage II: Two or more lymph node groups are involved, but all are on the same side of the diaphragm (the muscle separating the chest from the abdomen).
- Stage III: Lymph node groups on both sides of the diaphragm are affected, or the spleen is involved.
- Stage IV: The lymphoma has spread widely into organs outside the lymphatic system, such as the liver, lungs, or bone marrow.
PET-CT scans are the primary tool for staging in subtypes that light up on PET imaging, which most aggressive lymphomas do. For subtypes that don’t show strong PET activity, CT scans alone guide the staging. The tonsils, the ring of tissue at the back of the throat (Waldeyer’s ring), and the spleen are all considered part of the lymphatic system for staging purposes, so involvement in those areas doesn’t automatically push the stage higher.
Bone Marrow Biopsy for Staging
A bone marrow biopsy helps determine whether lymphoma has reached the marrow, which would indicate stage IV disease. During the procedure, a needle is inserted into the back of the hip bone to withdraw a small amount of liquid marrow (aspiration) along with a tiny core of bone tissue. Both samples are examined for lymphoma cells.
This procedure has become less universally required in recent years. For certain subtypes that are highly PET-avid, a PET-CT scan showing no activity in the bones may be enough to rule out marrow involvement, sparing you the biopsy. For other subtypes, particularly indolent (slow-growing) lymphomas that don’t always light up reliably on PET, bone marrow biopsy remains a standard part of staging.
The entire diagnostic process, from initial blood work through subtype confirmation and staging, typically takes one to several weeks depending on how quickly biopsies can be scheduled and how complex the pathology turns out to be. Rare or ambiguous cases may be sent to specialized hematopathologists for expert review, which can add time but significantly improves diagnostic accuracy.