Is Total Neutrophil Count (TNC) the same as Absolute Neutrophil Count (ANC)?

Total Neutrophil Count vs. Absolute Neutrophil Count

Total Neutrophil Count (TNC) and Absolute Neutrophil Count (ANC) are the same measurement, referring to the total number of neutrophils per unit volume of blood.

Understanding Neutrophil Counts

Neutrophils are a type of white blood cell that serve as the body's primary defense against bacterial infections. The neutrophil count is a critical parameter used in clinical medicine for several purposes:

• Monitoring risk of infection during neutropenia
• Guiding decisions about chemotherapy dosing
• Determining eligibility for certain treatments
• Monitoring response to growth factor therapy

Terminology Clarification

Both terms (TNC and ANC) refer to the same laboratory value and are used interchangeably in clinical practice. This is evident in multiple clinical guidelines:

• The ESMO guidelines define febrile neutropenia using ANC: "Febrile neutropenia is defined as a rise in axillary temperature to >38.5°C for a duration of >1 h while having an absolute neutrophil count (ANC) of <0.5 · 109/l" 1

• Similarly, other guidelines consistently use ANC when referring to the total number of neutrophils 1

Calculation of Neutrophil Count

The ANC/TNC is calculated by multiplying the total white blood cell count by the percentage of neutrophils (including both mature neutrophils/segmented neutrophils and immature neutrophils/bands):

ANC = WBC count × (% segmented neutrophils + % band neutrophils) ÷ 100

Clinical Applications

Defining Neutropenia Severity

The ANC is used to define the severity of neutropenia:

• Grade 0: ANC ≥ 2000/μL
• Grade 1: ANC 1500-2000/μL
• Grade 2: ANC 1000-1500/μL
• Grade 3: ANC 500-1000/μL
• Grade 4: ANC < 500/μL 1

Treatment Decisions

The ANC is crucial for clinical decision-making:

• Primary prophylaxis with growth factors is recommended when the risk of febrile neutropenia exceeds 20% 1
• Neutropenic patients with ANC < 500/μL and fever require prompt antibiotic therapy 1
• Chemotherapy dosing adjustments are often based on ANC values 1

Laboratory Considerations

Modern hematology analyzers can provide accurate and precise neutrophil counts even at very low levels (>0.1 × 10^9/L) 2. In some clinical settings, particularly hematology/oncology clinics, the ANC may be ordered as a standalone test rather than as part of a complete blood count with differential, as it provides focused information with shorter turnaround time 3.

Common Pitfalls

1. Confusing terminology: Some clinicians may use "total neutrophil count" to emphasize that both mature and immature neutrophils are included in the calculation.

2. Relying solely on percentages: The percentage of neutrophils can be misleading without considering the total white blood cell count. Always use the absolute count for clinical decisions.

3. Timing considerations: Neutrophil counts can fluctuate throughout the day and in response to stress, exercise, and medications. Consistent timing of blood draws can improve reliability.

4. Age variations: Normal neutrophil counts vary by age, with higher counts typically seen in newborns and lower counts in older adults 1.

In summary, TNC and ANC are identical measurements representing the total number of neutrophils in a given volume of blood, and either term may be used in clinical practice.