We often talk in the MS clinic about white blood cells, about leukocytes, lymphocytes, granulocytes and what they’re all called. But I always find that the background knowledge about these important cells is often incomplete, which can lead to considerable confusion. Since the control of white blood cells is of great importance in relation to many MS therapies, half-knowledge and the resulting confusion are often the source of great uncertainty. But to be fair, this uncertainty sometimes also exists on the part of the attending (primary care) physicians, which not infrequently leads to effective and sensible drugs for the treatment of MS being suspended – often out of fear of unpredictable side effects.
Therefore, a short digression about white blood cells might be quite useful at this point. I have noticed myself that much more confidence and serenity comes into MS therapy when I explain to my patients what can be deduced from the blood count and explain to them the significance of changes in the blood count.
In routine diagnostics, the “blood count” is one of the most frequently performed laboratory tests. In routine diagnostics, a small blood count is usually made, meaning the number of white blood cells (leukocytes), red blood cells (erythrocytes) and platelets (thrombocytes) are determined from venous blood. In addition, haemoglobin, the red blood pigment that binds oxygen, is determined. But that’s about it in terms of the information provided by the small blood count.
The entirety of white blood cells, i.e. the above-mentioned leukocytes, consists of various subgroups of white blood cells, namely the so-called granulocytes, lymphocytes and monocytes (they are named after the shape of their cell nuclei). These subgroups can be differentiated and counted in the laboratory – we then speak of the so-called differential blood count, in jargon also called “large blood count”.
These subgroups have different tasks in immune defence. The largest subgroup, the granulocytes, which make up about 70% of the white blood cells, are the first line of defence against germs and pathogens – they form, for example, the pus in infected wounds and their defensive effect is relatively unspecific. Granulocytes are not affected by most MS drugs and are therefore of lesser importance for monitoring during MS therapy.
MS drugs mainly affect the so-called lymphocytes, whose share of the total leukocyte count is approximately 25%. Lymphocytes are immune cells that have learned to react to specific pathogen components (we speak of antigens) during their life. Lymphocytes are thus essential components of acquired immunity and they are also responsible for autoimmune reactions. In MS, we assume that autoreactive lymphocytes trigger and maintain multiple sclerosis. Therefore, MS therapies often aim at reducing these cells. However, since these cells are also important for a normal immune response against various pathogens, they must not be attacked too severely with drugs – and therefore the counting of lymphocytes is important for therapy monitoring of MS patients. In the differential blood count, absolute numbers are usually not given, but only the proportional shares of the total leukocyte count, but with this you can calculate the absolute number.
A small example: Let’s assume that a total of 4000 leukocytes/µl are counted in a small blood count, of which 23 % are lymphocytes in the large blood count, then the absolute lymphocyte count is 4000 x 0.23 = 920 lymphocytes/µl. For this value, the absolute lymphocyte count, there are limit values for many MS drugs that should not be undercut (for Tecfidera e.g. 500 lymphocytes/µl). Therefore, we always look at this value during the checks (and are annoyed when no “large blood count was made – because with the small BB – as you now know – nothing can be done for the question).
With special techniques, the group of lymphocytes can be further differentiated, e.g. into T-lymphocytes and B-lymphocytes, and many other subgroups, but this differentiation is often reserved for special questions and is not considered in routine monitoring.
In the future I will – based on this – describe in more detail in further texts what to expect and consider with individual medications in terms of absolute lymphocyte counts. Until then, have fun calculating your lymphocytes….
