Audience

• Highland HSCP 

The reference range depends on age but in adults is generally 1 to 5 to 4 × 10⁹/L. In younger patients lymphocytosis is often reactive but this is less common in the elderly where a clonal (malignant) disorder is more likely. Please note that a normal full blood count does not rule out lymphoma.

Causes

• Viral infection
• Bacterial infection especially tuberculosis, pertussis
• Hyposplenism
• Smoking
• Stress response g. post myocardial infarction
• A lymphoproliferative disorder g. chronic lymphocytic leukaemia

History and examination

Review older blood tests. Ask about recent viral infections. Ask about weight loss, B symptoms, recurrent infections and smoking. Examine for lymphadenopathy and hepatosplenomegaly.

Suggested investigations

• Blood film
• Monospot if EBV suspected

Management

Repeat the full blood count in four to six weeks to look for resolution

• If there are recurrent infections, B symptoms, palpable lymphadenopathy, hepatosplenomegaly or associated cytopenia and lymphocytosis is persistent then refer to haematology
• If there are concerning blood film features reported by a haematologist please refer to haematology
• In older patients a persistent lymphocytosis most likely represents a haematological malignancy (e. non Hodgkin lymphoma). The most common malignancy is chronic lymphocytic leukaemia. There is no advantage of early treatment in these patients and therefore, depending on age and comorbidities, there is frequently no rush to make definitive diagnoses in patients with mild persistent lymphocytosis who are asymptomatic. Making a diagnosis of malignancy which may not influence life expectancy in asymptomatic patients may cause anxiety and affect insurance coverage.
• If the lymphocyte count is persistently above 10 × 10⁹/L suggest discussion via Clinical Dialogue to determine the best management strategy. 

If your patient is found to have chronic lymphocytic leukaemia based on a blood count and immunophenotyping they may not necessarily require referral to haematology. Please discuss via Clinical Dialogue. In general patients can be monitored in primary care if:

• No B symptoms
• No (or only minor) lymphadenopathy
• Normal haemoglobin, platelet and neutrophil count
• Stable lymphocyte count.

Reasons for re-referral to our department would be

• Doubling of the lymphocyte count in under a year (this is only relevant once the lymphocyte count is above 20)
• Please be aware the lymphocyte count can jump up temporarily as part of an intercurrent viral infection or if patients are on steroids. A rising lymphocyte count in isolation in the absence of any other concerning clinical or laboratory abnormalities is not a cause for concern.
• Anaemia with a haemoglobin of <100 (consider other causes of anaemia)
• Thrombocytopenia with a platelet count of <100
• B symptoms such as drenching night sweats or weight loss of more than 10% of body weight in six months
• Significant progressive lymphadenopathy: as part of early stage CLL or SLL it would not be surprising to have 1 to 2cms lymph nodes dotted throughout the nodal areas
• Single, rapidly enlarging lymph node mass: patients with CLL can occasionally develop transformation to a type of high grade lymphoma. Patients with high grade transformation usually present with a rapidly enlarging lymph node mass, significant B symptoms and a very high LDH.