In the clinical laboratory, there are few tests that clearly indicate the presence of lymphoma. The full blood count (FBC) may be used to exclude diseases other than lymphoma (such as leukaemia) or to see if anaemia or low platelet and/or white blood cell counts are present, which may indicate that lymphoma is present in the bone marrow. There is only one true diagnostic test for lymphoid neoplasms and that is for a pathologist to examine lymph tissue (usually from a lymph node) obtained by biopsy or fine needle aspiration.
Additional lymphoid tissue can be examined by further techniques.
Flow cytometry is another technique that can categorise cells by testing for the presence or absence of cell markers. These markers are called clusters of differentiation (CD) and each antigen is allocated a number. The pattern of CDs present on the cells helps to classify the lymphoma. For example, follicular lymphoma characteristically expresses CD20 and CD10 but not CD5 or CD23.
Immunohistochemistry is the technique of demonstrating antigens on cells in histological tissue sections.
Chromosome studies may show abnormalities specific for a type of lymphoma, for example, follicular lymphoma shows a translocation between two different chromosomes, 14 and 18, denoted t(14;18). Studies using a technique called Fluorescent In-Situ Hybridisation (FISH) uses chromosome 'paints' to mark when specific genes are missing, have extra copies or are joined together in the wrong way.
Other studies using the Polymerase Chain Reaction (PCR) which replicates strands of DNA, bring greater sensitivity and can look for specific genes joined together in the wrong way, or for those with subtle defects in their DNA.
Once a diagnosis of a lymphoid neoplasm is made, the stage of the disease is determined with the use of either computed tomography (CT) or Positron emission tomography (PET) scans. A bone marrow biopsy is also done to check if the lymphoma has spread to the bone marrow.