Low lymphocytes (lymphopenia): what the result means and what happens next

Lymphocytes are a type of white blood cell. They are part of the immune system, helping the body recognise and fight infections and remember them for next time. They are measured as part of a full blood count with a differential, which splits the white cell total into its different types.

A low count is called lymphopenia (or lymphocytopenia). It simply means the number is below the reference range used by the laboratory that ran the test. Ranges differ between laboratories, so the range printed next to your result is the one that matters. As an example, an NHS Dumfries and Galloway guide gives 1.5 to 3.5 x10 to the 9th per litre as normal for adults and classes 1.0 to 1.5 as mild and below 0.5 as severe.

The most reassuring point from UK pathways is how often it is harmless. The Dumfries and Galloway guide calls it a common non-specific finding that increases with advanced age and other health conditions, and says that in most cases it is a transient condition that does not require specialist input.

The causes listed in the NHS pathways used for this guide are broad. Where one of them is already known to be present, the York pathway says no further investigation is required.

• Recent or ongoing infection, including viral and bacterial infections, hepatitis, TB and HIV.

• Reactive causes such as trauma, surgery, and stress or intense exercise.

• Medicines, including steroids (also inhaled steroids), chemotherapy, rituximab and other immune-suppressing or monoclonal antibody drugs.

• Autoimmune conditions, sarcoidosis and inflammatory bowel conditions.

• Kidney, heart or liver failure and some cancers, including lymphoproliferative disorders.

• Alcohol excess, malnutrition and radiotherapy.

• Older age. The York pathway lists elderly patients (over 70 years with a count above 0.5) as a group where no further investigation is needed.

• Rare congenital immune disorders, which usually show up in childhood.

A mildly low count usually has no symptoms of its own. Any symptoms tend to come from the underlying cause, such as an infection. The Blood Project, a US educational resource, says that many people with mild lymphocytopenia feel completely well, and that symptoms when they occur usually reflect infection, such as fever or chills, cough, sore throat, skin infections or pain on passing urine. Because it is a US source, its numbers are quoted in different units and are not used on this page.

Severely low counts, or counts that are low in someone having chemotherapy or taking immune-suppressing medicines, matter more because the risk of infection is higher. Anyone in that situation should follow the advice given by their treating team about when to call.

The Dumfries and Galloway guide lists the usual assessment: history and examination looking for oral thrush, enlarged glands or an enlarged spleen or liver, and features of systemic disease; inflammatory markers such as ESR and CRP; HIV and viral hepatitis tests; and an autoimmune screen. Not everyone needs all of these.

For an isolated low lymphocyte count in an otherwise well person with a normal examination and negative tests, that guide says referral is not indicated and recommends repeating the full blood count in 6 months, with no further monitoring if there is no change. The York pathway similarly advises FBC monitoring only when the count is mild (0.5 to 1.5) in a well patient, for example 6-monthly at first, extending to annually if stable.

Review of medicines is also an important step, since several common drugs can lower lymphocyte counts. Do not stop any prescribed medicine without advice from the prescriber.

The pathways reserve haematology referral for cases where something else raises concern for a blood disorder. The York pathway lists unintentional weight loss, fevers in the absence of infection, drenching night sweats, recurrent infections with no other underlying cause, enlarged lymph glands or an enlarged liver and spleen, and other low blood counts. The Dumfries and Galloway guide refers for the presence of B symptoms, glands over 1 cm or an enlarged spleen.

If you notice any of these features, tell your GP rather than waiting for the routine repeat test. A GP can examine you and arrange further tests where needed.

If you are well and the count is mildly low, the general approach is simple follow-up. Good hygiene and prompt attention to symptoms of infection are sensible, as with any time of year. Keep a record of results so trends can be compared.

A full blood count is done routinely on the NHS when a GP requests it. Private health check packages also include it, but a result outside the range still needs interpreting alongside symptoms, medicines and any previous results, usually by a GP. If you have had a private test with an unexpected result, take the report to your GP so it can be put into context.