Family Medicine Board Review · Hematology · Source: AAFP 12/2025
Neutropenia: High-Yield Board Summary
ANC thresholds, the four classic pediatric/idiopathic causes side-by-side, management principles, G-CSF indications, and pediatric vaccination rules.
Definition
- ANC <1.5 × 10⁹/L in adults and children >1 year old
- ANC <1 × 10⁹/L in children <1 year old
Board trap: the ANC cutoff for neutropenia is lower in infants <1 year (ANC <1) than in older children/adults (ANC <1.5) — don't apply the adult threshold to a young infant.
Classification
Causes — Four Key Entities
1. Benign Ethnic Neutropenia
Incidental Chronic Mild Neutropenia
- Incidental finding of chronic mild neutropenia, in the absence of a secondary cause
- Common in the Middle East (and other populations of African descent)
- Associated with the Duffy null phenotype
- Usually causes persistent mild neutropenia
- Does NOT increase risk of infection
- Examination normal; extensive evaluation is not needed
Board trap: the Duffy null phenotype association is the single most testable fact here — a Middle Eastern or African-descent patient with incidental mild neutropenia, normal exam, and no infections needs no extensive workup.
2. Autoimmune Neutropenia
- Mostly occurs in children
- Typically resolves by age 2 years
- Characterized by antineutrophil antibodies acting against neutrophils
- Usually causes mild to moderate neutropenia
- Most of the time not associated with severe infection
- If antibodies are negative but autoimmune neutropenia is still suspected → consider bone marrow evaluation
3. Chronic Idiopathic Neutropenia
- Similar to autoimmune neutropenia, but with persistent neutropenia >3 months
- Negative antineutrophil antibodies
4. Cyclic Neutropenia
- Cyclical pattern — recurs approximately every 21 days
- Appears in the 1st year of life
- Repeated episodes of fever, malaise, oral ulcers, and skin infections
- Caused by apoptosis of myeloid precursors
- Diagnosis: serial CBCs twice weekly for at least 6 weeks, documenting two nadirs with return-to-normal ANC in between, to establish the cyclic pattern
- Severe infection is rare but requires urgent treatment when it occurs
- Treatment: daily G-CSF
Board trap: the diagnostic protocol — CBC twice weekly × 6 weeks, documenting 2 nadirs — is a specific, testable numeric detail. Don't confuse this entity's ~21-day periodicity and infancy onset with chronic idiopathic neutropenia (no cyclic pattern, more variable onset).
Age-Based Epidemiology
- Infants and children: neutropenia is often incidental, with benign etiologies such as primary autoimmune neutropenia
- Adults and older individuals: common causes are idiopathic, drug exposures, autoimmune conditions, infectious diseases, and malignancies
Exam pearl: the differential shifts meaningfully by age — a benign, self-limited process is the default assumption in a young child, while an adult with new neutropenia warrants a broader workup including drug causes and malignancy.
Medication Causes (General Knowledge)
Common Drug Classes Linked to Neutropenia
Antithyroid drugs (methimazole, propylthiouracil) · Antipsychotics (clozapine) · Antibiotics (trimethoprim-sulfamethoxazole, penicillins, cephalosporins) · Antiepileptics (carbamazepine, phenytoin) · NSAIDs · Chemotherapy agents · Sulfasalazine
Key Point
Comprehensive
medication reconciliation is a core part of the initial evaluation and management of any new neutropenia.
Note: this section's specific drug table wasn't extractable from your source file's image; the list above reflects standard clinical knowledge on drug-induced neutropenia, supplementing your document.
Physical Examination — Findings/Complications (General Knowledge)
- Fever
- Oral ulcers, gingivitis, periodontal disease
- Skin/soft tissue infections
- Lymphadenopathy
- Hepatosplenomegaly (raises concern for infiltrative/malignant process)
- Signs of underlying systemic or autoimmune disease
Note: this section's specific content wasn't extractable from your source file's image; the list above reflects standard clinical knowledge, supplementing your document.
Investigations (General Knowledge)
- CBC with differential (confirm and classify severity) + peripheral smear
- Repeat ANC to confirm persistence
- Antineutrophil antibodies (if autoimmune neutropenia suspected)
- Vitamin B12, folate, copper levels
- ANA and other autoimmune markers if systemic autoimmune disease suspected
- Viral serologies (HIV, EBV, CMV, parvovirus)
- TSH
- Bone marrow biopsy — reserved for atypical presentations, suspected marrow failure/infiltrative process, or antibody-negative suspected autoimmune neutropenia
Note: this section's specific content wasn't extractable from your source file's image; the list above reflects standard clinical knowledge, supplementing your document.
Management
- 1) Nutritional deficiencies should be addressed
- 2) Management of systemic illnesses should be optimized
- 3) Comprehensive medication reconciliation
4) Granulocyte Colony-Stimulating Factor (G-CSF)
- Used as primary prophylaxis in patients with a solid tumor or lymphoma who are starting chemotherapy
- Can be given in inherited neutropenia
Exam pearl: G-CSF's role spans both oncology (chemo-associated primary prophylaxis in solid tumor/lymphoma patients) and inherited neutropenic syndromes (e.g., cyclic neutropenia) — know both indications, not just the oncology one.
Immunization in Children
- For children with neutropenia <1.0 × 10⁹/L, live immunizations should be avoided
- All inactivated/attenuated vaccines can still be given — but be aware immunizations given while immunocompromised may be less effective at protecting
- If a child must avoid live vaccines, it's important to ensure those living in close contact with the child are fully immunized to protect them (cocooning strategy)
Board trap: the live-vaccine-avoidance threshold is specifically ANC <1.0 × 10⁹/L — a child with mild neutropenia (ANC 1.0–1.5) does not automatically require live vaccine deferral by this rule. Also remember: even inactivated vaccines given during neutropenia may generate a blunted immune response.