What are the causes and management of low neutrophil (absolute neutrophil count) and high lymphocyte (lymphocytosis) counts?

Causes of Low Neutrophils and High Lymphocytes

Low neutrophils (neutropenia) combined with high lymphocytes (lymphocytosis) suggests either viral infection, certain hematologic malignancies (particularly chronic lymphocytic leukemia or lymphoproliferative disorders), or primary/secondary immunodeficiency syndromes.

Primary Diagnostic Considerations

Viral Infections

• Acute viral infections are the most common cause of this pattern, characterized by transient lymphocytosis with relative or absolute neutropenia 1
• Common viral pathogens include EBV, CMV, HSV, VZV, and respiratory viruses 1
• Viral infections typically present with fever, constitutional symptoms, and self-limited course 1

Hematologic Malignancies

• Chronic lymphocytic leukemia (CLL) frequently presents with lymphocytosis and may have concurrent neutropenia from marrow infiltration 1
• B-cell lymphoproliferative disorders can cause persistent lymphocytosis with neutropenia 1
• Monoclonal gammopathy of uncertain significance (MGUS) occurs in 3.2% of individuals over age 50 and is associated with increased bacterial infections 1
• Diffuse large B-cell lymphoma (DLBCL) shows reduced lymphocyte counts overall but altered lymphocyte subsets, particularly decreased CD4+ T cells 2

Primary Immunodeficiency Syndromes

• Common variable immunodeficiency (CVID) can present with recurrent infections, lymphoproliferation, and abnormal lymphocyte counts 1
• Autoimmune lymphoproliferative syndrome (ALPS) presents with prominent lymphoproliferation and autoimmune disease 1
• X-linked lymphoproliferative syndrome (XLP) should be considered with lymphoproliferation features 1

Secondary Immunodeficiency

• Hypogammaglobulinemia secondary to B-cell lymphoproliferative disorders causes recurrent bacterial infections 1
• Patients with advanced or refractory malignancy receiving multiple chemotherapy regimens develop severe immunosuppression 1
• Nearly 90% of heavily pretreated CLL patients experience serious infectious complications requiring hospitalization 1

Management Algorithm Based on Neutrophil Severity

Severe Neutropenia (ANC <0.5 × 10⁹/L)

• Implement broad-spectrum prophylactic antimicrobial therapy immediately including fluoroquinolone with or without streptococcal coverage 3, 4
• Add antiviral prophylaxis (acyclovir or valacyclovir) against HSV and VZV 1, 4
• Consider antifungal prophylaxis (fluconazole) for prolonged neutropenia 4
• Consider G-CSF therapy at 5 mcg/kg/day subcutaneously if prolonged neutropenia is anticipated 1, 3
• Monitor CBC twice weekly during G-CSF therapy 4, 5

Moderate Neutropenia (ANC 0.5-1.0 × 10⁹/L)

• Close monitoring with weekly CBC for 4-6 weeks 3, 5
• No routine antimicrobial prophylaxis required unless additional risk factors present 5
• Evaluate for underlying causes including viral infections and hematologic disorders 5

Mild Neutropenia (ANC 1.0-1.5 × 10⁹/L)

• Regular CBC monitoring without antimicrobial prophylaxis 5
• Assess for symptoms suggesting infection, autoimmune disease, or hematologic malignancy 5

Essential Diagnostic Workup

Initial Laboratory Evaluation

• Complete blood count with differential to calculate absolute neutrophil count and absolute lymphocyte count 1
• Serum immunoglobulins (IgG, IgA, IgM) and serum protein electrophoresis to detect monoclonal proteins or hypogammaglobulinemia 1
• Lymphocyte subset analysis by flow cytometry to identify abnormal B-cell or T-cell populations 2

Immunologic Assessment

• Pneumococcal antibody levels before and 4-8 weeks after 23-valent pneumococcal vaccine to assess functional antibody response 1
• Failure to generate protective titers (>1.3 mcg/mL) to >70% serotypes indicates functional antibody deficiency 1
• Consider immunoglobulin replacement therapy if IgG <400 mg/dL or ≥2 severe recurrent infections by encapsulated bacteria 1

Viral Studies

• PCR-based viral panels for HSV, VZV, EBV, and CMV if infection suspected 1
• CMV DNA monitoring if reactivation risk suspected 1
• EBV DNA monitoring in cases of persistent fever and fatigue 1

Management of Febrile Neutropenia

If fever develops (>38.5°C for >1 hour) with ANC <0.5 × 10⁹/L, this constitutes a medical emergency requiring immediate hospitalization 1, 3, 4

• Discontinue prophylactic fluoroquinolone if being used 4
• Initiate empiric broad-spectrum antibacterial therapy with vancomycin plus antipseudomonal antibiotics (e.g., cefepime, piperacillin-tazobactam, or meropenem) 3, 4
• Obtain blood cultures, chest radiograph, and additional imaging as indicated 3
• Continue antibiotics until ANC ≥0.5 × 10⁹/L, patient afebrile for 48 hours, and blood cultures negative 4

Special Clinical Scenarios

Patients with Lymphocytosis and Recurrent Infections

• Screen for CLL with flow cytometry and peripheral blood smear 1
• Evaluate for hypogammaglobulinemia requiring immunoglobulin replacement 1
• Monthly IVIG treatment recommended until IgG levels ≥400 mg/dL 1

Patients with Autoimmune Features

• Consider ALPS, APECED, or IPEX syndrome with polyendocrine autoimmunity 1
• Evaluate for hemophagocytic lymphohistiocytosis (HLH) if fever, toxic appearance, and lymphoproliferation present 1

Patients Receiving Immunosuppressive Therapy

• Maintain acyclovir or valacyclovir prophylaxis throughout MM treatment 1
• Monitor for CMV reactivation in high-risk patients (post-transplant, alemtuzumab therapy) 1
• Withhold BsAb or chemotherapy dosing until neutrophil count returns to normal 1

Critical Pitfalls to Avoid

• Never delay evaluation of fever in neutropenic patients - even mild fever with severe neutropenia requires immediate attention 3, 4
• Do not overlook minor skin lesions in neutropenic patients as these can represent serious infections 3
• Avoid using serum IgG and IgM serology tests alone for viral infection diagnosis in patients with hypogammaglobulinemia - interpret with caution 1
• Do not use G-CSF during radiotherapy to the chest due to increased complications and death 1
• Avoid administering G-CSF immediately before or simultaneously with chemotherapy due to risk of severe thrombocytopenia 1
• Do not aim for ANC >10 × 10⁹/L during G-CSF therapy - discontinue if ANC exceeds this threshold 4, 5

Prognostic Considerations

• Higher neutrophil-to-lymphocyte ratio (NLR) predicts worse outcomes in various conditions including sepsis, COVID-19, and systemic sclerosis 6, 7, 8
• Lymphocyte count <1.26 × 10⁹/L increases susceptibility to infection 2
• Higher NK cell counts before treatment predict better therapeutic outcomes in DLBCL 2
• Patients with ANC <100 cells/μL for >7 days have highest risk for invasive fungal infections 3, 4