How should I evaluate a patient with persistent lymphocytosis, one month of fever, moderate anemia, and a lymphocyte-predominant leukocytosis?

Evaluation of Persistent Lymphocytosis with Fever, Anemia, and Lymphocyte-Predominant Leukocytosis

Obtain a peripheral blood smear immediately to assess lymphocyte morphology, followed by flow cytometry immunophenotyping to distinguish chronic lymphocytic leukemia from reactive causes, while simultaneously evaluating for hemophagocytic lymphohistiocytosis given the constellation of fever, anemia, and lymphocytosis. 1

Initial Diagnostic Algorithm

Step 1: Peripheral Blood Smear Examination

• Examine the blood smear first to determine whether lymphocytes appear small and mature (suggesting CLL) versus atypical, activated, or pleomorphic (suggesting reactive process or other lymphoproliferative disorder). 1, 2
• Look specifically for monomorphic versus pleomorphic lymphocyte populations—a monomorphic population favors a lymphoproliferative neoplasm. 2
• Enumerate any circulating blasts, immature granulocytes, or dysplastic features that would suggest acute leukemia or myelodysplastic syndrome. 2

Step 2: Flow Cytometry Immunophenotyping

• Flow cytometry is the single most important test to distinguish neoplastic from reactive lymphocytosis and should be ordered immediately. 1
• For suspected CLL, look for the characteristic pattern: CD5+, CD23+, CD20 dim+, surface immunoglobulin dim+, FMC7-. 1
• Patients with absolute lymphocytosis have a 93% positive flow cytometry rate for detecting lymphoproliferative disorders. 3
• If CLL is confirmed (sustained lymphocytosis >5 × 10⁹/L for ≥3 months with monoclonal population), proceed to CLL-specific workup. 1

Step 3: Exclude Hemophagocytic Lymphohistiocytosis (HLH)

Given the combination of one month of fever, anemia, and lymphocytosis, HLH must be excluded as it is potentially fatal if missed:

• Check the following HLH-2004 diagnostic criteria (5 of 8 required):

  • Fever ≥38.5°C
  • Splenomegaly (perform abdominal ultrasound or CT)
  • Cytopenias affecting ≥2 lineages (hemoglobin <9 g/dL, platelets <100,000/µL, neutrophils <1,000/µL)
  • Hypertriglyceridemia (≥265 mg/dL) and/or hypofibrinogenemia (≤150 mg/dL)
  • Ferritin ≥500 ng/mL
  • Soluble CD25 (sIL-2 receptor) ≥2,400 U/mL
  • Low or absent NK cell activity
  • Hemophagocytosis on bone marrow, spleen, or lymph node biopsy 4, 5

• Measure ferritin, triglycerides, fibrinogen, and soluble CD25 immediately—hyperferritinemia is particularly sensitive for HLH. 4, 5

• HLH can be triggered by infections (Rickettsia, CMV, EBV, dengue, tuberculosis), autoimmune disorders, or malignancies including lymphoproliferative disorders. 4, 6

Step 4: Exclude Secondary Causes of Lymphocytosis

• Rule out infections that cause reactive lymphocytosis: obtain viral serologies (EBV, CMV), blood cultures if febrile, and consider atypical infections. 1, 2
• Exclude corticosteroid use, which is a common iatrogenic cause of lymphocytosis. 1
• Check for autoimmune disorders, particularly if there is evidence of autoimmune hemolytic anemia (obtain direct antiglobulin/Coombs test). 1, 7

Additional Laboratory Studies Once CLL is Confirmed

If flow cytometry confirms CLL:

• Obtain LDH, β2-microglobulin, serum protein electrophoresis, Coombs test to assess prognosis and detect autoimmune cytopenias. 1
• Perform chest X-ray and abdominal ultrasound or CT to evaluate for occult lymphadenopathy and splenomegaly. 1
• Hepatitis B virus testing should be obtained if future immunotherapy or chemotherapy is anticipated. 8

Role of Bone Marrow Biopsy

• Bone marrow biopsy is NOT required to diagnose CLL if peripheral blood shows sustained lymphocytosis >5 × 10⁹/L with characteristic immunophenotype. 1
• Bone marrow biopsy IS indicated if:
  • HLH is suspected and hemophagocytosis needs to be documented 4, 5
  • Flow cytometry shows <20% blasts but clinical suspicion for acute leukemia or lymphoma remains high 8
  • Cytopenias persist after infection resolution and marrow infiltration by CLL needs assessment 7
  • Complete remission confirmation is needed in treated lymphoproliferative disorders (requires <30% lymphocytes, normocellular morphology, absence of lymphoid nodules) 9, 1

Critical Pitfalls to Avoid

• Do not delay flow cytometry in favor of bone marrow biopsy when peripheral blood lymphocytosis is present—flow cytometry on blood is diagnostic for CLL. 1
• Do not attribute fever solely to CLL without excluding infection or HLH; CLL itself rarely causes fever unless there is transformation or infection. 1, 4
• Do not overlook HLH in patients with fever, cytopenias, and lymphocytosis—this syndrome mimics sepsis and has high mortality if untreated. 4, 5
• Do not rely solely on absolute lymphocyte count—patients with initial counts <30 × 10⁹/L may require observation to determine lymphocyte doubling time. 1
• Do not perform fine-needle aspiration of lymph nodes if lymphoma is suspected; excisional biopsy provides superior tissue architecture for diagnosis. 8

When to Initiate CLL-Directed Therapy

Watch-and-wait is appropriate if CLL is confirmed without symptoms or significant cytopenias; monitor blood counts every 3 months. 1

Initiate CLL-directed therapy only when one or more of the following are present:

• Progressive marrow failure (hemoglobin <10 g/dL or platelets <100,000/µL)
• Massive splenomegaly (≥6 cm below left costal margin)
• Massive lymphadenopathy (≥10 cm longest diameter)
• Rapid lymphocytosis (>50% increase over 2 months or doubling time <6 months)
• Autoimmune cytopenias refractory to corticosteroids
• Significant constitutional symptoms (≥10% weight loss, ECOG ≥2, fever >38°C ≥2 weeks, or night sweats >1 month) 7

Special Consideration: Treatment-Related Lymphocytosis

• If the patient is already receiving BTK inhibitors (ibrutinib, acalabrutinib) or PI3K inhibitors (idelalisib, duvelisib), transient lymphocytosis does NOT signify disease progression—these agents cause early mobilization of lymphocytes from lymph nodes into blood. 9
• Prolonged lymphocytosis after ibrutinib represents persistence of a quiescent clone and does not predict early relapse. 9
• The revised IWCLL response criteria allow for "PR with lymphocytosis" in patients on these agents who show reduction in lymph nodes and splenomegaly despite persistent lymphocytosis. 9