Abnormal lymphocyte count can have various causes, ranging in severity from 'minor' to 'generally fatal'. Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.
Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms. In order to diagnose abnormal lymphocyte count, we could:
|Whooping Cough||2%||Ruled out|
|Infectious Mononucleosis||0%||Ruled out|
|Guillain-Barre Syndrome||0%||Ruled out|
|Herpes Simplex Type I||0%||Ruled out|
White Blood Cells - Lymphocyte Percentage [fraction]
Possible responses:→ Don't know
→ Under 20% [0.20] (low)
→ 20 to 45% [0.20-0.45] (normal)
→ 46 to 55% [0.46-0.55] (elevated)
→ Over 55% [0.55] (high)
Certain drugs, such as mephenytoin, dilantin and para-aminosalicylic acid, can cause an increased lymphocyte count. Certain drugs, such as steroids and chemotherapy drugs, can cause a decreased lymphocyte count. Levels should return to normal after stopping treatment.
Lymphocytes are made in the bone marrow, so when the bone marrow isn't functioning properly, lymphocyte counts can drop.
A study investigated the transformation of peripheral blood lymphocytes from patients with Myasthenia Gravis. The researchers found a decreased mitogen responsiveness of lymphocytes, suggesting that part of the lymphocyte function is subnormal in Myasthenia Gravis. [J Neurol Neurosurg Psychiatry. 1979 Aug; 42(8): pp.734-40]
Autoimmune problems such as rheumatoid arthritis can cause reduced lymphocyte counts.
A complete blood count may show large numbers of lymphocytes in a pertussis patient.