Monocytes migrate into the tissues where they become macrophages, with specific characteristics depending on their tissue localization.
Monocytopenia can increase the risk of infection, and it can indicate poor prognosis in patients with acetaminophen-induced hepatic damage and thermal injuries. Peripheral blood monocytopenia does not usually indicate a decrease in tissue macrophages; in some cases it can be associated with impaired granuloma formation in response to infections.
Monocytopenia can result from
Chemotherapy-induced myelosuppression (along with other cytopenias)
Hematopoietic cell mutation involving GATA2
Neoplastic disorders (eg, hairy cell leukemia, acute lymphoblastic leukemia Acute Lymphoblastic Leukemia (ALL) Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer; it also strikes adults of all ages. Malignant transformation and uncontrolled proliferation of an abnormally differentiated... read more
, Hodgkin lymphoma Hodgkin Lymphoma Hodgkin lymphoma is a localized or disseminated malignant proliferation of cells of the lymphoreticular system, primarily involving lymph node tissue, spleen, liver, and bone marrow. Symptoms... read more 
)Infections (eg, HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more
, Epstein-Barr virus infection Infectious Mononucleosis Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy. Fatigue may persist weeks or... read more 
, adenovirus infection Adenovirus Infections Infection with one of the many adenoviruses may be asymptomatic or result in specific syndromes, including mild respiratory infections, keratoconjunctivitis, gastroenteritis, cystitis, and primary... read more , miliary tuberculosis Miliary TB Tuberculosis outside the lung usually results from hematogenous dissemination. Sometimes infection directly extends from an adjacent organ. Symptoms vary by site but generally include fever... read more 
)Corticosteroid or immunoglobulin therapy
Gastric or intestinal resection
Transient monocytopenia can occur with endotoxemia, hemodialysis, or cyclic neutropenia.
Monocytopenia due to GATA2 mutation
A severe deficiency or absence of monocytes can occur in patients with mutations of the hematopoietic transcription factor gene, GATA2. Dendritic cells are decreased, and there may also be lymphocytopenia Lymphocytopenia Lymphocytopenia is a total lymphocyte count of 1000/mcL ( 1 × 109/L) in adults or 3000/mcL ( 3 × 109/L) in children 2 years. Sequelae include opportunistic infections... read more (mainly natural killer and B cells), or pancytopenia.
Despite near-absence of circulating monocytes, tissue macrophages are usually preserved. Also, immunoglobulin levels are usually normal even when circulating B cells are depressed. Bone marrow is hypocellular and can show fibrosis and multilineage dysplasia. Karyotypic abnormalities, including monosomy 7 and trisomy 8, may be present.
Infections with Mycobacterium avium complex (MAC) or other nontuberculous mycobacterial infections are common (MonoMAC syndrome). Fungal infections (ie, histoplasmosis Histoplasmosis Histoplasmosis is a pulmonary and hematogenous disease caused by Histoplasma capsulatum; it is often chronic and usually follows an asymptomatic primary infection. Symptoms are those... read more 
, aspergillosis Aspergillosis Aspergillosis is an opportunistic infection that usually affects the lower respiratory tract and is caused by inhaling spores of the filamentous fungus Aspergillus, commonly present in... read more 
) also are typical. Infections with human papillomavirus Human Papillomavirus (HPV) Infection Human papillomavirus (HPV) causes warts. Some types cause skin warts, and other types cause raised or flat genital warts (lesions of the skin or mucous membranes of the genitals). Infection... read more 
(HPV) may occur with subsequent risk of progression to secondary cancers. There is a high risk of progression to hematologic disorders (myelodysplasia Myelodysplastic Syndrome (MDS) The myelodysplastic syndrome (MDS) is group of disorders typified by peripheral cytopenia, dysplastic hematopoietic progenitors, a hypercellular or hypocellular bone marrow, and a high risk... read more , acute myeloid leukemia Acute Myeloid Leukemia (AML) In acute myeloid leukemia (AML), malignant transformation and uncontrolled proliferation of an abnormally differentiated, long-lived myeloid progenitor cell results in high circulating numbers... read more 
, chronic myelomonocytic leukemia, lymphomas Overview of Lymphoma Lymphomas are a heterogeneous group of tumors arising in the reticuloendothelial and lymphatic systems. The major types are Hodgkin lymphoma and non-Hodgkin lymphoma (see table Comparison of... read more ) with a resulting poor prognosis.
Unvaccinated patients should be given HPV vaccination Human Papillomavirus (HPV) Vaccine Human papillomavirus (HPV) infection is the most common sexually transmitted disease. HPV can cause skin warts, genital warts, or certain cancers, depending on the type of HPV. Vaccines are... read more . Any infections are treated with appropriate antimicrobials. Allogeneic hematopoietic stem cell transplantation Hematopoietic Stem Cell Transplantation Hematopoietic stem cell (HSC) transplantation is a rapidly evolving technique that offers a potential cure for hematologic cancers (leukemias, lymphomas, myeloma) and other hematologic disorders... read more is the treatment of choice and should be considered for patients who get frequent infections or with refractory cytopenias.
