Monday, November 20, 2006

Medical Stuff - Part 1: Haematology

Ok, I'll take the plunge and try to explain a bit about what Acute Lymphoblastic Leukaemia is and how Kezia is being treated. If I get anything wrong, and any of our readers are in the medical profession, please correct me through the Comments or by email.

First we need to take a look at blood. The study of blood is haematology. Haematologists are doctors who know a lot about blood. If you don't understand a bit about blood, you won't understand much about leukaemia.

Blood cells can be divided into three types: red (RBC), white (WBC and also known as leucocytes) and platelets (PLT). You'll see these abbreviations on lab reports so I'll start using them now.

When you whizz blood around at very high speed in a centrifuge, it separates out into these three types: white cells are white, red cells are red and platelets are a kind of bilious yellow.

Red cells are important for carrying oxygen and other nutritious things round your body. White cells defend your body against all the millions of things that would like to attack and eat you. Platelets are there to clot your blood if you cut yourself – those nasty scabs form because of platelets – if you didn't have them, you'd bleed until there was no blood left at all - which means you're dead.

The important ones as far as leukaemia goes are the white cells, and, sod's law, there's a bunch of different types which we need to get to grips with.

  • Neutrophils (MNEUT): these constitute around 65% of the WBCs. They defend you against bacterial infections and are the first ones to respond to an attack. Kind of like suicide bombers in that they die during the attack and turn into pus.
  • Eosinophils (MEOS): these constitute around 4% of the WBCs and defend against parasitic infections.
  • Basophils (MBASO): less than 1% of the WBCs. These are responsible for responses to allergies and release histamines causing inflammation.
  • Lymphocytes (MLYMPH): around 25% of WBCs. Divided into further sub-types.
    • B-cells - these make antibodies that bind to the attackers enabling their destruction. The arms factories.
    • T-cells - CD4+ (helper) cells coordinate the immune response – the generals telling the different troops where to go. CD8+ (cytotoxic) cells are the SAS of WBCs that kill virus infected cells. Natural Killers are the MI6 of WBCs. They can kill infected cells that are displaying a signal to the other troops not to kill them (hello I'm friendly! e.g. cancer cells).
  • Monocytes (MMONO): 6% of WBCs. These are similar to our MNEUTs but get to live a bit longer.

All of these are produced in the bone marrow. And they all derive from Hemopoietic Stem Cells (HSCs), also known as Hemocytoblasts. These cells split and form precursors of all of the above as well as the precursors of RBCs and platelets. The immediate precursors are known as blasts which then develop into the -cytes above before being thrown out into the blood to do their work.

In Acute Lymphoblastic Leukaemia something goes wrong with the HSCs. They start producing more and more lymphoblasts which never grow up into lymphocytes. The lymphoblasts take over all the space in the bone marrow allocated to the the other types of blasts – red, white and platelets. This gives rise to low RBC levels (anaemia) and low platelet counts (danger of bleeding).

They also head out into the blood. As they have not matured into lymphocytes, they can't fight the attackers as they should. Hence people with ALL are prone to infections.

Initial diagnosis is by a blood test - positive results show a large number of lymphoblasts. This is then confirmed by a bone marrow sample which, if positive, will also show a large number of lymphoblasts.

Other clinical signs are an enlarged spleen (WBCs accumulate here), anaemia (lack of RBCs) and a reduced platelet count.

No comments: