Autoimmune Diseases

»Neutropenia is seen in 5%–10% of healthy people
Based on absolute neutrophil count, neutropenia is commonly defined as
mild (1.0–1.5 × 109
/L), moderate (0.5–0.9 × 109
/L) or severe (< 0.5 × 109
/L).1
However, the reference interval is specific to the population. Mild asymptomatic neutropenia per the above definition is common in people of subSaharan African, Arab or West Indian ancestry,2
and is strongly associated
with the Duffy-null phenotype of red blood cells that protects against
Plasmodium vivax malaria.
2 Common causes include medications, infection, nutritional
deficiency, malignant disease and autoimmune disease
Causes include underproduction (e.g., myelodysplastic syndrome),
immune-mediated destruction or redistribution of neutrophils to the
endothelium and reticuloendothelial system. Antithyroid, anti-infective
and psychotropic drugs, as well as chemotherapy, are causes of druginduced neutropenia.3,4 Transient neutropenia may occur after acute
viral infection and typically resolves within 2 weeks. Joint swelling, rash,
bony pain, splenomegaly or lymphadenopathy may suggest malignant or
autoimmune disease.
3Investigation should begin with a repeat complete blood count
and peripheral blood film
Neutropenia is often identified incidentally. Persistent and unexplained
neutropenia requires further work-up for a range of causes, including
chronic viral infection (e.g., hepatitis, HIV) and nutritional deficiency (e.g.,
vitamin B12) (Appendix 1, available at www.cmaj.ca/lookup/doi/10.1503/
cmaj.220499/tab-related-content).
4 Treatment of mild neutropenia should be directed at the
underlying cause
Patients with mild neutropenia are not at substantially increased risk of
infection.5
The neutrophil count should be checked every 3–6 months for
at least 1 year to rule out progression to more severe neutropenia.
5 Patients with moderate-to-severe neutropenia for more than
6 months should be referred to a specialist
Patients with recurrent or severe bacterial infections (e.g., requiring hospital admission or intravenous antibiotics), abnormalities on peripheral blood
films (e.g., circulating blasts, hairy cells, large granular lymphocytes, dysplastic granulocytes) or pancytopenia also warrant referral to a specialist
(e.g., hematologist, internist, pediatrician).1
Febrile neutropenia (absolute
neutrophil count < 0.5 × 109
/L and an oral temperature > 38.0°C sustained
over 1 h) requires immediate treatment with broad-spectrum antibiotics.