Step 1. Calculate the absolute neutrophil count (ANC)
The ANC is not simply the total white blood cell (WBC) count. It represents the circulating mature and immature neutrophils that are actually available to fight bacterial infection. The formula is:
ANC = WBC × (% segmented neutrophils + % bands) ÷ 100
For this patient:
2,000 × (
18 +
4) ÷ 100 =
2,000 ×
22 ÷ 100 =
440/mm³.
This value is below the critical threshold of
500/mm³, which defines severe neutropenia. The platelet count of
110,000/mm³ is mildly reduced but does not change the ANC interpretation.
Step 2. Apply the febrile neutropenia criteria
Febrile neutropenia is diagnosed when a patient with an ANC below
500/mm³ (or expected to fall below that level within 48 hours) develops a fever. The temperature criterion is met by either:
- A single oral temperature of
38.3 °C or higher, or
- A temperature of
38.0 °C or higher sustained for at least
1 hour.
This patient’s temperature has remained between
38.1 °C and
38.2 °C from
14:00 to
16:20, which is more than
2 hours. Therefore, the sustained-fever criterion is satisfied even though she never reached
38.3 °C.
Step 3. Clinical interpretation
The patient has febrile neutropenia: ANC of 440/mm³ plus a sustained temperature of 38.0 °C or higher for over 1 hour. This is an oncologic emergency because the near-absence of neutrophils means the usual signs of localized infection—erythema, purulence, fluctuance, or infiltrate on chest radiograph—may be minimal or absent. The fever itself is often the only early signal of bacteremia.
Key point! In neutropenic patients, a low-grade fever that persists is just as significant as a single high spike. Do not wait for
38.3 °C if the temperature has been
38.0 °C or higher for over an hour.
Step 4. Immediate nursing and medical priorities
Febrile neutropenia carries a high risk of rapid progression to septic shock. The standard approach includes obtaining blood cultures from a peripheral site and from each lumen of any central venous catheter, urine culture, and any other clinically indicated cultures, then starting broad-spectrum intravenous antibiotics promptly—ideally within
1 hour of presentation. Empiric regimens typically target
Pseudomonas aeruginosa and other gram-negative organisms, with gram-positive coverage added based on institutional protocols and patient risk factors. The choice of a carbapenem-sparing regimen may be considered in stable patients, but the priority is timely initiation of an appropriate agent rather than a specific drug class.
Why the other options are incorrect
Option 1 (
360/mm³) miscalculates the ANC by using only segmented neutrophils and omitting bands. Option 3 (
1,560/mm³) appears to use the lymphocyte or total granulocyte percentage incorrectly. Option 4 (
440/mm³) calculates the ANC correctly but misapplies the fever criterion by failing to recognize that a temperature of
38.0 °C or higher sustained over
1 hour qualifies as fever in the neutropenic setting.
| Component | This patient | Febrile neutropenia threshold | Interpretation |
|---|
| ANC | 440/mm³ | Below 500/mm³ | Neutropenia present |
| Temperature | 38.1–38.2 °C for over 2 hours | 38.0 °C or higher sustained over 1 hour | Fever criterion met |
| Diagnosis | Febrile neutropenia | Requires cultures and IV antibiotics promptly | Oncologic emergency |
Pathophysiology link
Doxorubicin and cyclophosphamide are myelosuppressive agents that damage rapidly dividing hematopoietic precursors in the bone marrow. The neutrophil nadir typically occurs around day
10–14 after chemotherapy, which is exactly when this patient presents. With an ANC below
500/mm³, the innate immune system cannot contain even normal flora that translocate across the gastrointestinal mucosa. Fever in this context reflects systemic inflammatory activation without the usual neutrophil-mediated localizing signs, which is why empiric antibiotics must be started before culture results return.