Absolute Lymphocyte Count

White blood cells (WBCs or leukocytes) are immune cells that fight infections and protect your body. This test measures WBC count in synovial fluid (fluid surrounding joints). Elevated WBC in joint fluid suggests infection, inflammation, or autoimmune disease affecting that joint. Very high counts may indicate septic arthritis (bacterial infection), while moderate elevation could indicate rheumatoid arthritis or other inflammatory joint conditions. This specialized test helps diagnose the cause of joint pain or swelling.

Lymphocytes are a type of white blood cell crucial for the adaptive immune response, including B cells (which produce antibodies), T cells (which coordinate and carry out cell-mediated immunity), and NK cells (natural killer cells). This blood test counts lymphocytes as part of the complete blood count with differential. Elevated lymphocyte counts (lymphocytosis) may suggest viral infections, certain leukemias, or autoimmune conditions. Low lymphocyte counts (lymphopenia) can indicate immunodeficiency, bone marrow disorders, or the effects of immunosuppressive therapies.

CLSI (formerly NCCLS) document "Reference Leukocyte Differential Count (Proportional) and Evaluation of Instrumental Methods", 1992, recommend the use of variant lymphocytes rather than atypical or reactive lymphocytes.