Arneth Count for Neutrophils: Principle, Procedure, and Clinical Significance

Arneth count, developed by Joseph Arneth, is a hematological method that classifies neutrophils into five stages (N1–N5) based on their nuclear lobe count. It determines the percentage of neutrophils with one (N1), two (N2), three (N3), four (N4), or five or more lobes (N5), reflecting their maturity. On the basis of nuclear lobes, neutrophils are grouped into stages N1, N2, N3, N4, and N5. A left shift (↑N1–N3) indicates infections (e.g., sepsis) or inflammation due to immature neutrophils, while a right shift (↑N4–N5) signals anemia (e.g., vitamin B12 deficiency) caused by excess mature cells.

Arneth Count for Neutrophils: Classification of Neutrophil Nuclear Lobe Stages with Diagrams and Normal Range Percentages.

Stage	Nuclear Lobes	Diagram	Normal Range
Stage I (N1)	Nucleus is unilobed, typically appearing C- or U-shaped.		2–5%
Stage II (N2)	Nucleus is bilobed, with two lobes separated by slender strands.		20–30%
Stage III (N3)	Nucleus is trilobed, featuring three lobes divided by fine strands.		40–50%
Stage IV (N4)	Nucleus is tetralobed, with four lobes separated by thin strands.		10–15%
Stage V (N5)	Nucleus is pentalobed, with five distinct lobes and delicate intervening strands.		2–5%

Principle of Arneth Count

Neutrophils mature by increasing their nuclear segmentation. Younger cells (N1–N3) have fewer lobes, while older ones (N4–N5) are multilobed. Technicians examine Leishman/Wright-stained blood smears under oil immersion (100x). At least 100 neutrophils are counted in a zigzag pattern. If lobes are ambiguous, secondary markers are used:

• Granule density: Younger cells have more granules.
• Cell size: Neutrophils shrink with age.

Procedure

1. Prepare a thin peripheral blood smear and stain with Leishman or Wright’s stain.
2. Use low-power magnification to confirm even cell distribution.
3. Under oil immersion (100x), count at least 100 neutrophils in a zigzag pattern and classify them into five stages (N1–N5) based on the number of nuclear lobes.
4. Enter the counts in a table, calculate the percentage distribution for each stage, and optionally plot a graph to visualize maturation trends.

Clinical Significance of Arneth Count

The Arneth count is a hematological test that evaluates neutrophil maturity by categorizing cells according to the number of nuclear lobes. This assessment indirectly reflects bone marrow activity by distinguishing between younger and older neutrophils in circulation.

Shift to Left (Regenerative Shift)

When over 80% of neutrophils are classified as N1, N2, or N3 (indicating fewer lobes), it signifies a left shift.

• Indicates: Increased neutrophil production bone marrow hyperactivity (young neutrophils released early).
• Causes:
  • Acute infections (e.g., pneumonia, sepsis)
  • Tuberculosis
  • Inflammation, trauma, or hemorrhage
  • Exposure to irradiation

Shift to Right (Degenerative Shift)

When more than 20% of neutrophils fall into stages N4 and N5 (indicating more lobes), it denotes a right shift.

• Indicates: Decreased neutrophil production and bone marrow hypoactivity (prolonged neutrophil maturation).
• Causes:
  • Megaloblastic anemia (B12/folate deficiency)
  • Aplastic anemia
  • Septicemia
  • Chronic kidney/liver disease
  • Uremia