The Arneth count is a hematological method used for the classification of neutrophils based on the number of lobes present in the nucleus. It is the process in which neutrophils are grouped into different classes according to nuclear segmentation and this helps in understanding the age and functional status of the cells. In this method neutrophils having fewer nuclear lobes are considered young cells while those having more lobes are considered older cells.
It is based on the principle that the nucleus of neutrophils becomes more segmented as the cell remains longer in circulation. Arneth classified neutrophils into five classes (Class I to Class V) starting from cells with a single lobe to cells having five or more lobes. This distribution is referred to as Arneth index and it is expressed in percentage.
The Arneth count is used to study changes in blood during disease conditions. An increase in cells with fewer lobes is known as shift to the left and it indicates acute infection or inflammation. An increase in highly segmented neutrophils is called shift to the right and it is seen in conditions like vitamin B12 or folic acid deficiency and bone marrow depression. Although this method is rarely used at present it has historical importance and the terms left shift and right shift are still commonly used in clinical hematology.
The five stages of neutrophil classification in Arneth’s count are as follows–
1. Stage I (Class I / N1)– These are the youngest neutrophils with a single, unsegmented nucleus. The nucleus is usually curved or horseshoe shaped and segmentation is absent. These cells are considered immature forms.
2. Stage II (Class II / N2)– In this stage the nucleus is divided into two lobes. The lobes are connected by a thin chromatin filament. These cells are slightly more mature than Stage I cells.
3. Stage III (Class III / N3)– These neutrophils show three distinct nuclear lobes connected by fine chromatin threads. This stage represents fully mature neutrophils and normally forms the major proportion of circulating neutrophils.
4. Stage IV (Class IV / N4) – The nucleus is divided into four lobes. These cells represent older neutrophils which have remained longer in circulation.
5. Stage V (Class V / N5) -These are the oldest or hypermature neutrophils with five or more nuclear lobes. They are normally present in very small numbers and increase in conditions showing a shift to the right.
Principle of Arneth Count
The Arneth count is based on the principle that the age and maturity of neutrophils can be determined by the number of lobes present in the nucleus. When neutrophils are released from bone marrow they are young cells and possess a single, unsegmented nucleus. As these cells remain in the blood circulation the nucleus gradually becomes constricted and divided into two, three, four or more lobes.
In this method a stained blood smear is examined and neutrophils are classified into five classes according to the number of nuclear segments. The proportion of each class reflects the balance between formation of neutrophils in bone marrow and their removal from circulation. An increased number of cells with fewer lobes is referred to as shift to the left and it indicates increased bone marrow activity during acute infections. On the other hand predominance of cells with many lobes is called shift to the right and it suggests prolonged survival of neutrophils in blood as seen in vitamin B12 or folic acid deficiency and bone marrow depression.
Objectives of Arneth Count Test
- To study the maturity of neutrophils by classifying them into different stages based on nuclear lobes.
- To assess the functional activity of bone marrow by estimating the rate of neutrophil production and release.
- To detect a shift to the left which indicates an increase in young immature neutrophils seen in acute infections and inflammation.
- To detect a shift to the right characterized by increased hypersegmented neutrophils as seen in vitamin B12 or folic acid deficiency and bone marrow depression.
- To monitor the progress of disease and response to treatment by observing changes in neutrophil distribution.
Requirements for Arneth Count Test
- Fresh whole blood sample collected preferably with anticoagulant like EDTA.
- Clean glass slides for preparation of thin blood smear and a spreader slide.
- Absolute methyl alcohol for fixation of the blood smear.
- Romanowsky type stain such as Leishman stain or Wright stain (Giemsa stain may also be used).
- Buffer solution or aged distilled water for dilution of stain and proper staining reaction.
- Compound light microscope for examination of stained smear.
- Oil immersion objective lens (100×) for clear observation of nuclear lobes.
- Immersion oil (cedar wood oil) for use with oil immersion lens.
- Differential counter or tally sheet for counting and classification of neutrophils.
Procedure of Arneth Count Test
- Prepare a thin peripheral blood smear on a clean glass slide by wedge method.
- Allow the smear to air dry and fix it with absolute methyl alcohol for two to three minutes.
- Stain the fixed smear with Romanowsky stain such as Leishman or Wright stain using buffer solution.
- Wash the slide gently with buffer or distilled water and allow it to dry.
- Place a drop of immersion oil on the stained smear and examine under oil immersion objective.
- Scan the smear in a zig-zag manner to avoid repeated counting of same cells.
- Count at least 100 neutrophils and classify them into Class I to Class V based on nuclear lobes.
- Record the number and calculate the percentage of each class to detect shift to left or right.
Result of Arneth Count Test
The result of Arneth count test is expressed in terms of percentage distribution of neutrophils classified into five stages based on the number of nuclear lobes. After counting at least 100 neutrophils the percentage of each class is calculated and interpreted.
Normal Arneth Count
In normal healthy individuals neutrophils show a balanced distribution.
- Stage I (one lobe) – about 2 to 10%.
- Stage II (two lobes) – about 20 to 30%.
- Stage III (three lobes) – about 40 to 50% and this forms the major group.
- Stage IV (four lobes) – about 10 to 15%.
- Stage V (five or more lobes) – about 2 to 5%.
Shift to the Left
When there is an increased percentage of neutrophils with fewer nuclear lobes mainly Class I II and III it is called shift to the left. This condition indicates acute infection inflammation hemorrhage or increased bone marrow activity.
Shift to the Right
When there is an increased percentage of neutrophils with four or more nuclear lobes mainly Class IV and V it is known as shift to the right. This finding is commonly seen in vitamin B12 or folic acid deficiency bone marrow depression uremia and liver diseases.
Clinical Significance of Arneth Count
- It helps in assessing the functional activity of bone marrow by studying the maturity pattern of neutrophils.
- It is useful in detecting shift to the left which indicates increased number of immature neutrophils seen in acute pyogenic infections hemorrhage trauma and active inflammation.
- It helps in detecting shift to the right characterized by increased hypersegmented neutrophils as seen in vitamin B12 or folic acid deficiency bone marrow depression liver disease and uremia.
- It is useful in monitoring the course of bacterial infections and recovery by observing changes in neutrophil distribution.
- It helps in differentiating allergic asthma from bacterial or bronchial asthma based on neutrophil pattern and eosinophil count.
- It may be used as a supportive test in screening vitamin B12 deficiency especially in patients under long term drug therapy.
Uses of Arneth Count
- It is used to evaluate the maturity of neutrophils by classifying them into five stages based on nuclear lobes.
- It helps in assessing the functional activity of bone marrow and the rate of neutrophil production.
- It is useful in diagnosing acute infections by detecting a shift to the left as seen in pyogenic infections sepsis pneumonia and tuberculosis.
- It is used in diagnosing megaloblastic anemia by detecting shift to the right due to hypersegmented neutrophils caused by vitamin B12 or folic acid deficiency.
- It helps in monitoring the progress of disease and response to treatment by observing changes in neutrophil pattern.
- It is used to differentiate allergic asthma from bacterial or bronchial asthma based on neutrophil distribution.
- It may be used for monitoring drug therapy especially in patients receiving long term medications causing vitamin B12 deficiency.
- It is helpful in the study of tropical diseases such as malaria and yellow fever which show marked shift to the left.
- It aids in differentiating infectious and non infectious arthritis by modified neutrophil counts.
- It helps in detecting conditions like bone marrow depression chronic liver disease and uremia associated with shift to the right.
Advantages of Arneth Count
- It provides a simple method for assessing the maturity pattern of neutrophils based on nuclear segmentation.
- It helps in evaluating the functional activity of bone marrow and the rate of neutrophil production.
- It allows early detection of megaloblastic anemia by identifying hypersegmented neutrophils before other blood changes appear.
- It is useful in monitoring the course of acute bacterial infections by observing shift to the left.
- It has prognostic value as repeated counts help in assessing response to treatment and recovery.
- It can show significant pathological changes even when total white blood cell count remains normal.
- It is helpful as a screening test for vitamin B12 deficiency in patients on long term drug therapy.
Limitations of Arneth Count
- It is a subjective test and the result depends on individual observer judgment while identifying nuclear lobes.
- It is difficult to distinguish thin chromatin filaments from thick nuclear bands leading to personal error.
- It is a time consuming and laborious manual procedure requiring skilled personnel.
- Overlapping of nuclear lobes in a two dimensional blood smear may cause difficulty in proper classification.
- Normal values vary with age race and physiological conditions which may lead to misinterpretation.
- The number of nuclear lobes does not always correlate with functional efficiency of neutrophils.
- The test has limited use in modern laboratories as it is largely replaced by automated hematology analyzers.
Neutrophil Classification Systems and Maturation Stages
| Classification System | Stage or Class | Nuclear Morphology | Maturity Level | Normal Range Percentage | Clinical Significance |
| Arneth Count | Stage I (N1) | Unsegmented nucleus; typically C-, U-, or horseshoe-shaped (band or stab form). | Immature | 5%−10% (up to 8%) | Increase indicates Left Shift (Regenerative or Degenerative); indicative of acute infection, inflammation, or bone marrow hyperactivity/stimulation. |
| Arneth Count | Stage II (N2) | Two distinct segments or nuclear lobes connected by a thin filament. | Mature | 20%−30% | Increase contributes to Left Shift; associated with acute bacterial infections, toxaemia, or early response to infection. |
| Arneth Count | Stage III (N3) | Three distinct nuclear lobes connected by filaments. | Fully mature | 40%−50% | Represents the “mature middle” of the population; functionally most efficient. Normal predominance in healthy adults. |
| Arneth Count | Stage IV (N4) | Four distinct nuclear lobes. | Mature | 10%−15% | Increase indicates Right Shift; suggestive of slowed production, megaloblastic anemia, or normal mature form. |
| Arneth Count | Stage V (N5) | Five or more distinct lobes; hypermature. | Hypermature | 2%−5% (less than 3%) | Increase indicates Right Shift (Degenerative Shift); signals B12/folate deficiency, chronic disease, or hypersegmentation. |
| Schilling Classification | Myelocyte | Round nucleus. | Immature | 0% | Absent from normal blood; presence indicates a regenerative shift to the left. |
| Schilling Classification | Juvenile (Metamyelocyte) | Indented nucleus, kidney-bean shaped. | Immature | 0%−1% | Increase indicates acute infection or regenerative left shift. |
| Schilling Classification | Stab Cell (Band) | T, V, or U-shaped nucleus; non-segmented. | Younger form | 3%−5% | Increase defines a left shift; indicates inflammatory response. |
| Schilling Classification | Segmented | Multilobed nucleus (2−5 lobes). | Mature | 51%−67% | Decrease relative to immature forms indicates shift to the left. |
| Cooke-Arneth Count | Class I | Nucleus with no true lobulation; lobes joined by more than a thread are counted as one. | Immature | 10% | Left shift (increase in Class I and II) indicates toxemia. |
| Filament-Nonfilament Count | Nonfilamented | Nuclei connected by broad bands rather than thin filaments. | Immature | 8%−16% | Percentages over 50% carry a guarded prognosis, often terminating fatally in septic cases. |
| Filament-Nonfilament Count | Filamented | Two or more nuclear masses connected by a thin filament of chromatin. | Mature | 84%−92% | Predominant type in healthy individuals. |
| Hypersegmentation Criteria | Hypersegmented | Six or more lobes (or >3% with five lobes). | Hypermature | 0% | Right shift; indicates Megaloblastic anemia (B12/folate deficiency), MDS, or Myeloproliferative disorders. |
| Traditional Laboratory Terminology | Left Shift | Increased bands, metamyelocytes, and myelocytes. | Immature | Not in source | Acute bacterial infection, severe inflammation, or tissue damage. |
| Traditional Laboratory Terminology | Right Shift | Predominantly mature neutrophils with hypersegmented nuclei. | Hypermature | Not in source | Vitamin B12 or folate deficiencies, chronic inflammation, or hydroxycarbamide use. |
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