How do you diagnose lymphoma using blood tests?

How to Diagnose Lymphoma Using Blood Tests

Blood tests alone cannot definitively diagnose lymphoma—tissue biopsy remains mandatory for diagnosis—but specific blood work is essential for initial evaluation, staging, and risk assessment. 1, 2

Blood Tests Cannot Replace Tissue Diagnosis

The fundamental principle is that lymphoma diagnosis must be made on the basis of a surgical specimen/excisional lymph node or extranodal tissue biopsy, not blood tests. 1 Core biopsies may only be appropriate as the sole diagnostic test in rare patients requiring emergency treatment. 1 This is because immunohistochemistry (CD45, CD20, CD3) on tissue is mandatory for proper classification according to WHO criteria. 1

Required Blood Tests for Lymphoma Evaluation

While blood tests don't diagnose lymphoma, they are required components of the diagnostic workup:

Essential Laboratory Studies

• Complete blood count (CBC) with differential to assess for cytopenias or abnormal cell populations 2, 3, 4

  • Anemia is present in 42% of NHL patients at diagnosis 5
  • Leukopenia occurs in 6%, thrombocytopenia in 13% 5
  • These findings may suggest bone marrow involvement but don't confirm lymphoma 5

• Lactate dehydrogenase (LDH) as a marker of tumor burden and for prognostic purposes 1, 2, 3

• Uric acid to assess tumor burden and risk of tumor lysis syndrome 1

• Comprehensive metabolic panel including liver and renal function tests 2, 3

• Protein electrophoresis is recommended for B-cell lymphomas 1, 2

Mandatory Infectious Disease Screening

• Hepatitis B, C, and HIV screening is mandatory before initiating rituximab therapy 1, 2, 3

Prognostic Value of Blood Abnormalities

Blood test abnormalities provide prognostic information but not diagnostic confirmation:

• Anemia is associated with shorter survival regardless of bone marrow involvement 5
• Thrombocytopenia correlates with shorter survival only when bone marrow is involved 5
• Multiple cytopenias (present in 8% of patients) indicate poor prognosis 5
• Circulating lymphoma cells appear in peripheral blood in 9.5% of cases but don't alter survival compared to other bone marrow-involved patients 5

Special Circumstances: When Blood Findings Suggest Lymphoma

In low-grade lymphomas and chronic lymphocytic leukemia, malignant lymphocytes may appear in peripheral blood and can be differentiated microscopically from normal lymphocytes. 6 Three morphologic types may be recognized: mature lymphocytic type, lymphoplasmocytic type, and lymphocytic type with prominent nuclear alterations. 6 However, even when suspected morphologically, diagnosis must be verified by flow cytometry for B-cell lymphomas or T-cell receptor gene rearrangement for T-cell disorders. 6

Critical Pitfall to Avoid

Never attempt to diagnose lymphoma based solely on blood tests. Even when circulating lymphoma cells are visible or CBC abnormalities are present, tissue biopsy with immunohistochemistry remains the gold standard. 1, 4 Blood tests serve to stage disease, assess prognosis, screen for contraindications to therapy, and monitor for complications—not to establish the diagnosis.