Lymphocytosis (lymphocytes > 4 G/L in adults)

Laboratory tests

• FBC with blood film
• ASTif needednon-French guidelineRecent fever, sore throat, fatigue or jaundice suggesting a viral infection (mononucleosis, hepatitis): the Lothian pathway combines liver function tests and viral serology in primary care ^[2].
• ALTif needednon-French guidelineRecent fever, sore throat, fatigue or jaundice suggesting a viral infection (mononucleosis, hepatitis): the Lothian pathway combines liver function tests and viral serology in primary care ^[2].
• GGTif needednon-French guidelineRecent fever, sore throat, fatigue or jaundice suggesting a viral infection (mononucleosis, hepatitis): the Lothian pathway combines liver function tests and viral serology in primary care ^[2].
• Alkaline phosphataseif needednon-French guidelineRecent fever, sore throat, fatigue or jaundice suggesting a viral infection (mononucleosis, hepatitis): the Lothian pathway combines liver function tests and viral serology in primary care ^[2].
• Monospot test or EBV serology (if mononucleosis-like syndrome or febrile sore throat)if needednon-French guidelineSore throat, fever, cervical lymphadenopathy or mononucleosis-like syndrome reported on the blood film: look for primary EBV infection ^[2].
• CMV IgG and IgM serology (if mononucleosis-like syndrome without EBV)if neededMononucleosis-like syndrome or prolonged fever with a negative mononucleosis spot test: look for recent CMV infection ^[2] (covered by the French laboratory fee schedule (NABM) when recent infection is suspected ^[3]).
• HIV serology (if risk factor or mononucleosis-like syndrome)if needednon-French guidelineAt-risk exposure, mononucleosis-like syndrome or unexplained fever: primary HIV infection may cause lymphocytosis; the Lothian pathway includes HIV in the viral serology ^[2].
• Hepatitis B serology (HBsAg, anti-HBc)if needednon-French guidelineCytolysis on the liver function tests or at-risk exposure: the Lothian pathway includes hepatitis B and C in the viral serology ^[2].
• Hepatitis C serologyif needednon-French guidelineCytolysis on the liver function tests or at-risk exposure: the Lothian pathway includes hepatitis B and C in the viral serology ^[2].
• Pertussis PCR on nasopharyngeal sample (paroxysmal cough, infant or contact)if needednon-French guidelineParoxysmal cough or contact with a case, especially in young infants, in whom pertussis is accompanied by leucocytosis ^[4]: see also the page “Whooping cough (suspected)”.

In 3 months

• FBC with blood film (repeat)

Laboratory tests

• FBC with blood film
• Blood lymphocyte immunophenotyping (search for a monoclonal B population)
• Refer to a haematology consultation, non-urgently, to confirm the diagnosis (enclose previous FBCs).

Every 6 to 12 months (depending on progression)

• FBC with blood film
• Reticulocyte count
• Haptoglobinif neededOnset of anaemia: look for autoimmune haemolytic anaemia, a complication of CLL ^[6].
• Bilirubinif neededOnset of anaemia: look for autoimmune haemolytic anaemia, a complication of CLL ^[6].
• LDHif neededOnset of anaemia: look for autoimmune haemolytic anaemia, a complication of CLL ^[6].
• Direct Coombs testif neededOnset of anaemia: look for autoimmune haemolytic anaemia, a complication of CLL ^[6].
• Serum protein electrophoresis (if infections)if neededInfectious complication: look for hypogammaglobulinaemia ^[6].

• Hyperlymphocytosis with general symptoms, lymphadenopathy or splenomegaly (adult); unexplained petechiae or hepatosplenomegaly (child); infant with whooping cough and hyperleucocytosis: urgent specialist opinion.