What does an absolute neutrophil count (ANC) of 13 indicate?

An Absolute Neutrophil Count of 13 cells/µL Indicates Profound, Life-Threatening Neutropenia

An ANC of 13 cells/µL (0.013 × 10⁹/L) represents profound severe neutropenia requiring immediate hospitalization, empiric broad-spectrum antimicrobial therapy, and consideration of granulocyte colony-stimulating factor (G-CSF). This value is far below the threshold for severe neutropenia and places the patient at extreme risk for life-threatening bacterial, fungal, and opportunistic infections 1, 2.

Classification and Severity

• Severe neutropenia is defined as ANC <0.5 × 10⁹/L (500 cells/µL) 1, 2
• An ANC of 13 cells/µL is approximately 40 times lower than the severe neutropenia threshold, representing profound immunosuppression 3
• This level falls into the most critical category where infection risk is maximal and mortality is substantially elevated 2

Immediate Management Algorithm

Step 1: Assess for Fever and Clinical Instability

• If fever >38.5°C for >1 hour is present, this constitutes febrile neutropenia—a medical emergency requiring immediate hospitalization 1, 2
• Evaluate for hemodynamic instability, altered mental status, or organ dysfunction suggesting sepsis 4
• Even without fever, patients with ANC this low require urgent evaluation as they may not mount typical inflammatory responses 2

Step 2: Initiate Empiric Antimicrobial Therapy

• Immediately start broad-spectrum antibiotics directed at gram-negative bacteria, particularly Pseudomonas aeruginosa 2
• Add antifungal prophylaxis (fluconazole) given the profound neutropenia 2
• Consider antiviral therapy (acyclovir or congeners) for herpes simplex virus prophylaxis 2
• Do not wait for culture results or fever development before initiating therapy at this ANC level 2

Step 3: Implement G-CSF Therapy

• Administer G-CSF at 5 mcg/kg/day subcutaneously 2
• Continue until ANC recovers to ≥0.5 × 10⁹/L with stable counts 2
• Monitor CBC twice weekly during G-CSF therapy 2
• Discontinue if ANC exceeds 10 × 10⁹/L to avoid excessive leukocytosis 2

Step 4: Identify and Address Underlying Cause

• Review recent chemotherapy, radiation, or immunosuppressive medications 5, 6
• Consider bone marrow examination with cytogenetics if etiology unclear 6
• Evaluate for hematologic malignancies (leukemia, myelodysplastic syndrome) 3
• Assess for autoimmune neutropenia with neutrophil antibody testing in appropriate clinical context 6, 7

Critical Monitoring Parameters

• Continue antimicrobial prophylaxis until ANC recovers to ≥0.5 × 10⁹/L 2
• Monitor for breakthrough infections despite prophylaxis 2
• If fever develops, discontinue prophylactic fluoroquinolone and escalate to empiric therapy per febrile neutropenia protocols 2
• Discontinue antibiotics only when: ANC ≥0.5 × 10⁹/L, patient asymptomatic, afebrile for 48 hours, and blood cultures negative 2

Special Considerations and Pitfalls

Common Pitfalls to Avoid

• Do not delay antimicrobial therapy waiting for fever or positive cultures—at ANC 13 cells/µL, patients lack sufficient neutrophils to mount typical inflammatory responses 2
• Avoid gut decontamination with antibiotics unless specifically indicated, as altering gut flora may worsen outcomes 2
• Do not aim for ANC >10 × 10⁹/L with G-CSF therapy, as this provides no additional benefit and increases risk 2

Context-Specific Management

• In hairy cell leukemia patients with ANC <1.0 × 10⁹/L, therapy initiation is typically indicated before counts decline further 3
• Patients with chronic granulomatous disease may have negative galactomannan assays despite invasive aspergillosis 2
• Those receiving mold-active antifungal prophylaxis may have poor predictive value of serum galactomannan screening 2

Long-Term Risks

• Patients with severe chronic neutropenia, particularly those responding poorly to G-CSF, have increased risk of developing myelodysplastic syndrome or acute myeloid leukemia and require ongoing monitoring 6
• Long-term G-CSF use carries a small increased risk of myelodysplastic syndrome or acute myeloid leukemia 2

Prognosis and Recovery Expectations

• Treatment should be delayed until ANC reaches >1.0 × 10⁹/L if chemotherapy-related, with dose reductions necessary if severe neutropenia persists 5
• Recovery timeline varies by etiology: chemotherapy-induced neutropenia typically recovers within 1-2 weeks with G-CSF support 5
• Patients with congenital neutropenia responding poorly to G-CSF may require hematopoietic stem cell transplantation 6