Lymphocytopenia: Causes, Symptoms, and Diagnosis of Low Lymphocyte Count

Lymphocytopenia (lymphopenia) is an absolute lymphocyte count (ALC) <1,000/µL in adults (<3,000/µL in children). Lymphocytes (T, B, NK cells) are central to adaptive immunity.

Causes

• Infections: HIV (CD4+ depletion), TB, viral (measles, hepatitis), sepsis
• Malignancy: Leukemia, lymphoma, metastatic cancer (bone marrow infiltration)
• Autoimmune: SLE, RA, Sjögren's, myasthenia gravis
• Iatrogenic: Corticosteroids (redistribution), chemotherapy, radiation, biologics (rituximab, alemtuzumab), transplant immunosuppression
• Nutritional: Protein-energy malnutrition, zinc deficiency
• Splenectomy: Loss of splenic reservoir
• Congenital: SCID, DiGeorge, ataxia-telangiectasia

Symptoms

• Recurrent/unusual infections (viral, fungal, intracellular bacteria)
• Fatigue, weight loss, fever, night sweats
• Poor wound healing

Diagnosis & Management

• CBC with differential → flow cytometry (T/B/NK subsets)
• HIV test, immunoglobulin levels, vaccine titers
• Treat underlying cause; prophylactic antibiotics (TMP-SMX) if CD4 <200
• IVIG for humoral deficiency; growth factors (G-CSF) not for lymphopenia

Lymphocytopenia is a sign, not a diagnosis. Identify and address the root cause.