Hi, does anyone have any knowledge about Red blood cell distribution width (RDW) in blood tests. Are they standard in NHS blood tests. How useful are they in diagnosis of b12, folate and iron deficiencies?
If MCV isn't always reliable when you have iron and b12 and/or folate deficiency. Could RDW be a better option.
Thanks.
The RDW tells you how similar your red blood cells are in size. On its own it's pretty useless.
Where it can be useful is when a mixture of macrocytic and microcytic anaemias might be present. Macrocytic anaemia can be caused by a lack of B12 or folate and results in large blood cells. Microcytic anaemia can be caused by a lack of iron and results in small blood cells.
If you have both types of anaemia (as is often the case with Pernicious Anaemia) you can have a mix of large and small red cells. When the average is measured (the Mean Cell Volume, or MCV) it can look normal.
That's when the RDW comes into play, because it will be higher than normal if there's a wide range of red cell sizes.
RDW can also be raised with iron deficiency anaemia on its own, but then MCV sill be low.
Hi. Scientist, not medic, but I was there when the RDW came into being! Here's a few of the dull bits if you can bear it.
The RDW is in effect the coefficient of variation of the width of the red cell size distribution [with a bit of a fiddle factor included.] Typically, when your blood is stable, the RDW will be somewhere between 12 and 15 [depending on the analyser design and technology].
When you start running out of something [iron, for example] you start making smaller [and smaller] red cells. Red cells last about 115 days, so each day you replace about 1% of them. If you're churning out smaller ones each day, then the RDW will rise, because the distribution has widened. That goes on until around day 60 for example, when you've got equal shares of big & little ones, and then as the small ones become the majority, the RDW trends down again. It may max out at over 30, before going down again. Sometimes the analyser can be confused. If you have two peaks then it may only give the width of one of them, because it found a valley in the middle of the distribution. Once you start treating the deficiency, the number rises again, the MCV rises, and eventually settles a few weeks later. If we're talking about B12 or folate deficiency, the explanation's the same but the distribution goes the other way as the cells are bigger. Along with all the other numbers in an FBC, it can be quite useful, but only if someone takes notice of it... A rising RDW on treatment is a good thing; it shows you're responding.
I almost understood that. It's fascinating. My MCV was 98fl last year and now 92fl after taking iron supplements all year because my gp told me I was borderline anemic. I've got the vampire look. I always have low iron results but can my blood results tell me why. Is it just iron deficiency, or iron deficiency because of low b12 or folate. Can you tell that without RDW. As I don't have this. Or do you need to do you need to do something like an iron panel to understand why you're low.
There are many possible causes of iron deficiency anaemia, but a lack of B12 or folate is not one of them. Trying to figure out which cause is responsible for yours is something that will require a lot of information, apart from blood tests.
The most common causes are not putting enough iron into the body (through not eating enough of it, or not absorbing enough of it) and too much iron leaving the body (heavy periods or intestinal bleeding being the most common.
[Scientist's recollection of lecture].
My lecturer summed up Iron Metabolism with a mnemonic. 'NATURE'.
Nutrition; Absorption; Transport; Utilisation; Reproduction; Exsanguination. Then it's easy to ramble on about each stage [which, thankfully, I won't today.]
It's such a fine balance that it's easy to tip over into negative iron balance. One millilitre of red cells lost equates to one milligram of iron lost. I remember that one particular surgical unit used to send us so much blood for analysis, so regularly, that patients developed iron deficiency in addition to their other problems. At least nowadays, we use far smaller sample volumes.
Do I need to stop giving my blood away.
Providing it's for a good reason then giving it away is fine, so long as you're not giving too much of it.
Working in a Pathology lab years ago, it was fairly common practice to be used as a guinea pig for various tests. It's something that is probably highly unlikely nowadays. I still have the scars.
It's important to remember that Iron Deficiency Anaemia isn't a condition in its own right; it's a symptom of something else.
I remember a junior medic who took aspirin daily, and regularly suffered GI blood loss. He knew what was causing it and accepted it, until it became rather more florid, and he was admitted with anaemia. When he stopped taking aspirin, the bleeding stopped and he recovered. [No, I don't know why he was taking it.]
It's worth considering that if you are anaemic due to lack of iron, replacing the iron will increase your use of folate and B12 in the short term because they're required to make more red cells.
As for the numbers reported from an analyser, laboratories try to keep it simple for the user and don't report every value that comes out of the machine. The RDW might, in your case, be one of those.
Trying to find enough space on a paper report to include all the relevant data has become more and more difficult.
I have ulcerative colitis but this hasn't been active for a few years now. I feel really unfit but I'm only 39, not overweight. I can hear my heart beat in my ears, get out of breath just talking. Constant palpitations. I may just be unfit.
Sorry for this, but the print's just too small for me, and if I enlarge it, it doesn't help!
Much better. I can read them. I would guess that somewhere, a decision has been taken to limit the actual amount of data that gets into your record, but I would be very surprised if there wasn't a great deal more of it. It's either the lab reducing the amount of data, or the surgery trimming it back.
Back in the late 60s, a full blood count consisted of 7 values. As the years went by, every 'next generation' of analyser generated more and more numbers, many of which were simply looking for something to do. Needless to say, some of the stuff is occasionally very interesting.
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