Why do lupus patients have low white cell counts, and what is the significance of this?
In SLE, antibodies directed against white cells are very common. A lower than normal lymphocyte count is found on the full blood count in about 95% of lupus patients. This is due to the presence of antibodies to lymphocytes which results in the destruction of the antibody-coated lymphocytes. Fortunately this rarely causes a clinical problem because more lymphocytes are released from the bone marrow where they are made. This means that there are enough lymphocytes to fight infection, especially those due to viruses like influenza ('flu'). However, high doses of certain drugs can also cause destruction of lymphocytes and, because the bone marrow where these cells are made is also attacked by such drugs, there may not be enough lymphocytes to light infection. So in this case there is an increased risk of infections, especially viral infections. Cyclophosphamide, which is sometimes used to treat more severe forms of lupus such as kidney disease, can have this effect. Consequently the white cell count is regularly checked in people receiving this drug so that the drug dose can be adjusted if necessary.
Low neutrophil counts are less common than low lymphocytes counts as a result of lupus and is more common in people of Afro-Caribbean origin (even in the absence of lupus). Low neutrophil counts can also be the result of drugs such as cyclophosphamide and azathioprine and if severe can be associated with bacterial infections such as pneumococcal pneumonia. Again, regular blood monitoring tests will usually prevent this complication by allowing the drug dose to be adjusted before a problem occurs.
