White blood cells (WBCs) in our body help fight infections. There are various types of WBCs and each has its own way of fighting microbial infections. The most important WBC is called the neutrophil.
The number of neutrophils in the blood is expressed as absolute neutrophil count (ANC) and it measures the percentage of neutrophils in the differential WBC count. The ANC of a healthy individual falls in the range of 2,500 to 6,000 per microliter.
A total blood count gives the levels of the three types of blood cells - white blood cells, red blood cells, and platelets. Neutrophils are present in two forms – polys and bands. Polys are also known as segmented neutrophils and are the most abundant of the WBCs. Bands are also called stabs and are immature polys. Both polys and bands destroy invaders (i.e. microbes) in the body.
The ANC is calculated by multiplying the number of WBCs in blood by the percentage of total neutrophils. For example, for a WBC count of 7000 per microliter, if neutrophils constitute 40% of the WBCs, the ANC in this case will be 7000 × 0.40 = 2800 per microliter.
An ANC below 1,000 per microliter is called neutropenia. ANCs less than 500 per microliter significantly increase the risk of infection. In cancer patients, frequent blood tests are performed to assess WBC count and ANC to monitor the body’s response to cancer treatment.
Chemotherapy, aimed at treating cancer, is one of the most common causes of neutropenia or abnormally low neutrophil count. Chemotherapy-driven neutropenia can make patients prone to infections and hence needs to be monitored and managed effectively.
Neutrophils are produced in the bone marrow, a spongy tissue present inside large bones in our body. Any factor that hinders the production of neutrophils can cause neutropenia. In addition to leukemia and/ or chemotherapy, factors such as some congenital disorders, myelodysplastic syndromes, chronic idiopathic neutropenia, and vitamin deficiencies can cause neutropenia. Infections such as HIV, Malaria, Hepatitis A, B, and C, Lyme disease, and Salmonella infection can also be a cause of neutropenia. Some autoimmune disorders like rheumatoid arthritis, and some antibiotics destroy neutrophils and thus may lead to neutropenia.
Neutropenia is usually diagnosed as part of a blood test ordered by the doctor for an existing condition. Once neutropenia is discovered, other tests might be ordered which might reveal the cause of illness. Doctors usually advise some precautions, such as washing hands frequently and wearing a face mask in patients with neutropenia, because they are vulnerable to microbial infections.
Neutrophils constitute nearly 55 to 70% of the total WBC count. Acute infections or trauma are the main triggers for production of neutrophils leading to elevated WBC count also known as neutrophilia or neutrophil leukocytosis.
In cancer patients, ANC is a reflection of the immunologic status of the patient in response to chemotherapy. This therapy suppresses production of WBC and hence neutrophils, thus increasing infection risks. Hence, a low ANC or neutropenia can be an indication of the need for reducing chemotherapy dosage or delaying the next sessions of chemotherapy. ANC also allows prediction of neutropenia-related events including fever after chemotherapy sessions. It thus offers a clear picture of the patient’s immunologic status.
ANC helps determine the need for antibiotics or other measures along with therapy to decrease complications related to neutropenia. While for an in-patient, a low ANC may be an indicator of the need to isolate the patient so as to protect him or her from exposure to infectious agents, in case of an out-patient, it can highlight the need to keep away from crowds or people having flu or colds. ANC is thus a powerful monitoring tool in cancer patients who are prone to bone marrow suppression due to radiation, chemotherapy, or bone marrow transplant.