It’s alright, ma, I’m only bleeding

The Biotutors discussion forum was getting hot and bothered last week over blood. Someone had wondered whether it would be OK to allow a student to test for blood glucose levels. The advice offered was almost unanimous – NO! Absolutely not! Do not touch with a barge pole! Too dangerous! So many ethical issues! No, no, no, no, NO.

All of which fills me with despair. After all, what could be more interesting, what could be more motivating or exciting, than looking at your own blood? Allowing and enabling students to do this should probably be a requirement of the A-level course. It’s very easy, it’s completely safe and it is utterly fascinating. Risk assessment? Yes, it needs to be sterile (easy). It’s advisable to get parental permission in advance (try this letter template blood typing letter for blog). It obviously has to be an “opt in” activity (in 15 years, I’ve never had a student opt out). Sometimes a student faints (be aware of this, watch out for it, ask them to alert you if they start feeling faint, and deal with appropriately if it happens). But there is absolutely no reason why you shouldn’t do it. Still not sure? Well, the ASE and CLEAPPS are both perfectly happy with it and have published procedures for taking blood samples safely. You can do it!

Now, if you’ve never done this, I can see why it might seem a bit intimidating, so it obviously makes sense to trial it on yourself/other teachers before rolling it out for a class. You also need to think about the class. I’m happy to do it with my Year 10s – you might prefer to keep it for the 6th form.

I also demo it on myself in the lesson, partly to show that I’m not asking them to do something I can’t or won’t do myself, but also to run through the protocol for them all to see. You can make this reasonably dramatic and play it for laughs (if you’re like me).

So I tell them about the bad old days when you literally had to summon up the nerve to jab yourself with a lancet. It wasn’t easy! Pushing the button on a plastic spring-loaded pre-set single use disposable captive lancet ( is a doddle by comparison.

I say they need to choose a “sacrificial” finger. I reassure them that sensation will return in a year or two. Probably. The disposable lancets have 3 depth settings, so you can determine the length of the steel blade that will plunge into your flesh – …. I ask my class to select the appropriate length for their teacher. They take great delight in always choosing the longest one.

Use the side of your finger. The pad of the finger has far too many nerve endings and will be quite sore afterwards. The top of the finger, just behind the nail, just seems too close to the bone! The side of the finger, about half way along the last phalange, is nice and fleshy, has lots of capillaries, but is relatively un-sensitive.

It’s good to shake your arm thoroughly before stabbing yourself, to encourage blood flow. Sterilise the side of your finger with the sterile cleansing wipe ( Place the lancet firmly against the stab site on the sacrificial finger…

… and then….

… press the button. It’s instantaneous. You might feel a little jab, you might feel nothing at all, but it’s actually a huge anti-climax after all that build up. But! You should have blood. If it seems a tad slow emerging, then squeezing, or “milking” your finger can encourage the flow; after all, you’re not going to need very much. Or you might be a bleeder – take what you need and then stop the flow (pressure followed by a plaster).

So, you’ve got blood. What are you going to do with it?

The obvious thing is to look at it. I do this in year 10, when they just look at the red blood cells. All they need, apart from their blood, is a slide, a drop of saline, a coverslip and a microscope. And simply watching the little biconcave discs spinning in the plasma (you actually see the cells in 3D, which you don’t get from a prepared slide) is pretty compelling, even soulful. It also gives an immediate impression of the tiny-ness and numerous-ness of cells – there are at least 4 million cells per micro-litre, but even at x400, they are very, very small.

I do this again in Year 12, when they learn to stain with Leishmans’ to show up the white blood cells. What are the relative numbers, red vs white? How many different types of white blood cell can they identify? Using haemocytometers is a good option here, too. The motivation levels are sky high.

So looking at blood is very cool. But there’s more.

Why not measure blood glucose? It couldn’t be easier – after all, it’s something diabetics routinely do several times a day. When I’ve had a diabetic student in the class, they’re usually only too delighted to talk about their condition, demonstrate what they do and explain how it affects their lives. A simple electronic blood-glucose monitor, which you can pick up in Boots, does the job admirably (though you need to check every year that the disposable test strips haven’t expired).

This is what I do.

I like to use a volunteer who measures their blood glucose and then drinks a Coke/eats a Mars bar. We record the time and the mmol/litre reading on the board. Then it’s time to review digestion/absorption. What do they think the next reading will be and why?  When we’ve finished this discussion, about ten minutes later, we test the same student again. Whoosh! Look at that sugar spike! I always make this very dramatic. Oh no! If we exceed 11 mmol/litre then it’s hyperglycaemic coma and death!!! Aarrghhhh!!!! This prompts lots of good questions and discussion about why high glucose levels are dangerous. Hmmm, time to check again. Oh. It’s falling. Hurray! They’ll live!

But what’s going on?

Again, record the data, time and concentration and start talking about what is happening inside that student at that very moment. With 4 or 5 more measurements before the end of the lesson, all the students have the data plot a suitable graph for homework, adding annotations to explain/describe what’s actually going on in the volunteer’s body along the line. I also ask them to extrapolate the line to show how they think it will change over the next 6 hours. It’s a brilliant way of testing their understanding, forcing them to think about data gathered in real time. What’s not to love?

And then there’s blood groups. I use this as the taster lesson for Year 11s thinking about A-level Biology. The blood typing kits from Blades ( are very easy to use and interpret. And what a brilliantly synoptic topic! We’re talking about membranes and membrane-proteins and genetics and inheritance and multiple alleles and antibodies and resistance to cholera and Charlie Chaplin and allele frequency and selection pressures and Anne Boleyn and the utterly brilliant blood typing game… ( Difficult, challenging, fascinating. Biology, in other words.

Next week, pregnancy!


2 thoughts on “It’s alright, ma, I’m only bleeding

  1. paulweeks2014 Post author

    So the suggestion is that Anne Boleyn might have been Rhesus negative – if Henry was Rhesus positive, as he almost certainly was, then the first child (Elizabeth) will also be Rhesus positive. She’s fine, but if her blood contacts Anne’s blood (i.e. at birth), then Anne’s immune system makes antibodies against the Rhesus positive protein. Future fetuses are attacked by these antibodies – result, lots of miscarriages and a decapitated queen.



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