In an immunocompromised patient with an invasive systemic fungal infection, what complete blood count abnormalities are typically observed?

CBC Picture of Fungal Infection in Immunocompromised Patients

In immunocompromised patients with invasive systemic fungal infections, profound thrombocytopenia (platelet count 30–50 × 10³/µL) accompanied by pancytopenia is the most characteristic CBC finding, particularly in neutropenic hosts with hematologic malignancies. 1

Hematologic Abnormalities

Thrombocytopenia (Most Common Finding)

• Profound thrombocytopenia with platelet counts typically ranging from 30–50 × 10³/µL occurs far more frequently than any other CBC abnormality in systemic fungal infections among immunocompromised patients 1

• Thrombocytopenia often accompanies pancytopenia caused by underlying chemotherapy, bone marrow transplantation, or hematologic disease rather than the fungal infection itself 1

• Platelet counts <100,000 cells/mm³ were documented in 41% of patients with disseminated histoplasmosis in a large institutional review 2

• The mechanism involves multiple pathways: platelet sequestration via phagocytosis and hypersplenism (particularly in hepatosplenic candidiasis), cytokine-mediated myelosuppression, direct fungal effects on megakaryocyte development, and consumptive coagulopathy from angioinvasive fungi 1

Neutropenia

• Severe neutropenia (<500 cells/µL) lasting longer than 7 days is the most critical risk factor for developing systemic fungal infections, not merely a consequence of the infection 3

• Profound neutropenia (<100 cells/mm³) persisting for 10–15 days places patients at highest risk for fungemia 4

• Neutropenia is typically pre-existing due to chemotherapy or underlying disease, creating the immunocompromised state that permits fungal invasion 5, 3

Anemia

• Hemoglobin <10 g/dL was present in 29% of patients with disseminated histoplasmosis 2

• Anemia develops as part of the pancytopenia picture in patients receiving myelosuppressive therapy 1

Leukocytosis (Less Common)

• Peripheral white blood cell count <3,000 cells/mm³ occurred in 28% of disseminated histoplasmosis cases, indicating leukopenia is more typical than leukocytosis 2

• Marked leukocytosis may suggest leukocyte adhesion defect rather than typical fungal infection presentation 5

Associated Laboratory Abnormalities

While not part of the CBC, these findings frequently accompany the hematologic picture:

• Elevated liver enzymes: ALT >60 U/L in 39%, AST >60 U/L in 27%, alkaline phosphatase >200 U/L in 55% of disseminated histoplasmosis patients 2

• Hypoalbuminemia (<3.5 g/dL) in 70% of cases 2

• Elevated C-reactive protein commonly accompanies the clinical picture of possible fungemia 5

Clinical Context and Pitfalls

Critical Diagnostic Considerations

• Do not attribute thrombocytopenia solely to chemotherapy or underlying malignancy without evaluating for invasive fungal infection, particularly when fever persists despite broad-spectrum antibiotics 1

• The CBC abnormalities are highly nonspecific and cannot distinguish fungal from bacterial bloodstream infections clinically 4, 6

• Daily complete blood counts are recommended for neutropenic patients with suspected or confirmed invasive fungal infection to track platelet trends and inform transfusion decisions 1

Organism-Specific Patterns

• Disseminated fusariosis presents with features similar to disseminated aspergillosis in neutropenic patients with acute myeloid leukemia, with the same pancytopenic picture 5

• Candidemia and disseminated candidiasis show the typical thrombocytopenia pattern, with up to 13% developing hemorrhagic cutaneous lesions when platelet counts become critically low 1

• Mucormycosis requires surgical debridement even with severe thrombocytopenia (platelet count <20–50 × 10³/µL), necessitating aggressive platelet support 1

Diagnostic Approach Beyond CBC

• Blood cultures have limited sensitivity (30–50% for candidemia, rarely positive for aspergillosis) and should not be relied upon exclusively 5, 4

• Tissue biopsy, galactomannan, and β-D-glucan assays are required for accurate detection, as reliance on blood cultures alone is insufficient 1

• Bronchoalveolar lavage, transthoracic needle aspiration, or video-assisted thoracoscopic biopsy are standard procedures for establishing diagnosis of invasive pulmonary aspergillosis 5