Lymphocyte percentage: high and low results explained

Lymphocytes are white blood cells that sit at the heart of adaptive immunity. According to Lab Tests Online UK, they are more specifically acting killers of infection that regulate the immune response, and some of them produce antibodies that remember previous infections and guard against re-infection with the same organism. They are active against bacteria, fungi, parasites and viruses.

On a blood count, the lymphocyte percentage is the proportion of all white cells that are lymphocytes. In healthy adults, neutrophils make up the largest share and lymphocytes come second, so the lymphocyte figure is a sizeable slice of the differential and tends to move noticeably when the balance shifts.

Percentages are linked to one another, because they must add up to one hundred. If the neutrophil count falls, the lymphocyte percentage rises even if the number of lymphocytes is unchanged. This is the main reason that reports include an absolute lymphocyte count, and why that absolute number is the one clinicians use.

The differential is produced automatically with every full blood count. The lymphocyte figure draws attention when someone has a long-lasting sore throat, swollen glands, persistent fatigue, repeated infections, a suspected immune problem, or when a blood condition is being investigated or monitored.

Treatments also bring it into focus. People receiving chemotherapy, steroid courses or immune-suppressing drugs have their counts followed so that clinicians know how well their defences are holding up.

No fasting or special preparation is required. A nurse or phlebotomist takes blood from a vein in the arm, or from the heel in infants. Lab Tests Online UK points out that age, eating, physical activity and stress may alter differential values.

Children normally have a higher lymphocyte proportion than adults, so the same percentage can be ordinary in a child and unusual in an older person. Reference intervals printed on the report reflect the age group, and results should be compared against those intervals rather than against general figures.

Lab Tests Online UK says lymphocytes can increase in cases of bacterial or especially viral infection, leukaemia, lymphoma and in people with underactive or absent spleens. In its full blood count guide it adds that a high count can occur with viral infections or with chronic lymphocytic leukaemia.

Glandular fever is a classic example. The NHS describes it as a viral infection that mostly affects teenagers and young adults, with symptoms such as high temperature, swollen glands, sore throat and tiredness, and notes that a blood test may be ordered to confirm it. Blood counts during glandular fever often show a lymphocyte-predominant picture, and the haematology laboratory may comment on unusual-looking lymphocytes on a film.

A persistently raised absolute lymphocyte count in an older adult who feels well is sometimes the first clue to a slowly progressing blood condition. That is uncommon, but it is the reason that sustained rises are followed up with a blood film and sometimes flow cytometry rather than being ignored.

Lab Tests Online UK states that decreased lymphocyte levels are common in later life but can also be due to steroid medication, stress, lupus, and HIV infection. Chemotherapy, radiotherapy and some severe illnesses also lower lymphocyte numbers, often temporarily.

A low percentage, as opposed to a low absolute count, can occur simply because neutrophils are high during a bacterial infection. If your neutrophils are raised and the lymphocyte percentage is low but the absolute number is within range, nothing is wrong with your lymphocytes.

After an infection, counts commonly settle within weeks without any treatment, and a repeat full blood count confirms this. If the absolute count stays outside the range, the laboratory may examine a film, the doctor may check for viral causes such as Epstein-Barr virus, cytomegalovirus or HIV, and your medicines will be reviewed.

Where a blood condition is suspected, referral to haematology is the next step. Urgent advice applies if a low white cell count comes with a fever, since infection can progress quickly in people whose defences are reduced; the NHS advises seeing a GP if you know you are at risk and develop an infection.