Monocytosis

Definition/Description

An increase in the number of monocytes circulating in the blood. Monocytosis is frequently transient.

 

Causes

  • Infections e.g. tuberculosis, brucella, malaria, syphilis, endocarditis
  • Autoimmune and inflammatory diseases, including sarcoidosis
  • Stress response e.g. post myocardial infarction
  • Hyposplenism
  • Chronic myelomonocytic leukaemia
  • Solid malignancy

Red Flag Symptoms

None provided

Guidelines on Management

History and examination

Look for signs of infection including atypical infections. Ask about a travel history. Examine for splenomegaly and hepatomegaly. Ask about weight loss, rashes and night sweats. Look at older blood counts – there may be a previous blood film review.

 

Suggested investigations

  • Blood film
  • Inflammatory markers
  • Renal and liver function, calcium

 

Management

Persistent monocytosis without obvious underlying cause, particularly with normal inflammatory markers, may represent chronic myelomonocytic leukaemia. A blood film is the first investigation. Some cases behave indolently, particularly in the very elderly, so not every patient requires haematology review.

 

Referral Criteria/Information

Suggest haematology referral or A&G (according to clinical scenario) if:

  • Persistent monocyte count over 5 × 109 /L without underlying infective/inflammatory disorder
  • Monocyte count over 1.2 × 10^9 /L with additional cytopenias, splenomegaly or abnormal features on blood film

Associated Policies

There are no associated policies.

Specialties

Haematology York

Places covered by

  • vale-of-york

Hospital Trusts

  • york-and-scarborough-teaching-hospitals
Author: Dr Annika Whittle, Consultant Haematologist
Date created: 02/07/2025, 13:10
Last modified: 02/07/2025, 13:42
Date of review: 2027/9/30