How do you differentiate a bilobed (two-lobed) neutrophil from a lymphocyte?

Differentiating a Bilobed Neutrophil from a Lymphocyte

A bilobed neutrophil is distinguished from a lymphocyte primarily by its larger size (12-15 μm vs 7-10 μm), multilobed nuclear morphology with connecting chromatin bridges, coarse/clumped chromatin pattern, and abundant cytoplasm with fine granules, whereas lymphocytes have a single round nucleus with smooth contours, dense homogeneous chromatin, and scant cytoplasm.

Nuclear Morphology

Bilobed Neutrophil:

• The nucleus shows two distinct lobes connected by a thin chromatin bridge or filament 1
• Nuclear chromatin appears coarse and clumped with a characteristic "checkerboard" pattern 2
• The lobes are asymmetric and may show irregular contours 2
• This represents an intermediate maturation stage between band forms and fully segmented neutrophils (3-5 lobes) 1

Lymphocyte:

• The nucleus is single, round to slightly oval, with smooth regular contours 3
• Chromatin is dense, homogeneous, and deeply basophilic without the clumped pattern seen in neutrophils 3
• Small nucleoli may occasionally be visible but are typically inconspicuous 3

Cytoplasmic Features

Bilobed Neutrophil:

• Cytoplasm is moderately abundant and appears pale pink to colorless on Wright-Giemsa stain 1
• Contains fine azurophilic and specific granules that give a "ground glass" appearance 1
• The cytoplasm-to-nucleus ratio is higher than in lymphocytes 2

Lymphocyte:

• Cytoplasm is scant, forming only a thin rim around the nucleus 3
• Appears deeply basophilic (blue) on Wright-Giemsa stain 3
• May contain occasional azurophilic granules in activated lymphocytes, but lacks the fine granulation of neutrophils 3

Cell Size

• Bilobed neutrophils measure 12-15 μm in diameter, similar to other mature neutrophils 1
• Lymphocytes are smaller, typically 7-10 μm (small lymphocytes) or up to 12 μm (large lymphocytes) 3
• When comparing cells of similar size, nuclear and cytoplasmic features become the primary distinguishing characteristics 3

Common Pitfalls to Avoid

Do not confuse bilobed neutrophils with binucleated lymphocytes:

• Binucleated lymphocytes (seen in conditions like persistent polyclonal B-cell lymphocytosis) have two completely separate nuclei without connecting chromatin bridges 4
• Binucleated lymphocytes typically show basophilic cytoplasm and may have nucleoli, unlike neutrophils 4
• The chromatin pattern in binucleated lymphocytes remains mature and homogeneous, not clumped like neutrophils 4

Recognize that bilobed forms are immature neutrophils:

• Bilobed neutrophils represent band forms or early segmented forms in the neutrophil maturation sequence 1
• Their presence in increased numbers may indicate a "left shift" suggesting infection or inflammation 5, 6
• Functional capabilities differ from fully mature segmented neutrophils, with chemotaxis being the last function to develop 1

Clinical Context

• The neutrophil-to-lymphocyte ratio (NLR) is clinically significant, with normal values between 1-2 5
• When counting differential cells, bilobed neutrophils should be classified as neutrophils (either bands or segmented forms depending on the degree of nuclear constriction) 1, 6
• In stress states, surgery, or sepsis, marked neutrophilia with lymphopenia creates dramatically elevated NLR values, often with increased bilobed/band forms 5, 6