
Because you can’t push a needle up the vein in the elbow pit aka antecubital fossa yourself. You’d end up twisting the needle or doing it at a bad angle. At least in the forearm, wrist or the leg, you’d have a better chance at getting the needle in without doing too much damage to the vein or veins surrounding it. Also with all due respect, doctors don’t usually do the blood tests themselves. The elbow pit gets the best amount of blood fastest and it’s the easiest place for a nurse or phlebotomist to draw blood from. But if you’d try to do it yourself, you wouldn’t be able to do a good blood draw. Heroin users might have a better chance but they usually inject in rather than suck out. I’m a pretty curious person (hence forensics) and ask my nurses all the time when I get a blood test (like every month or twice a month at this point) about certain things to do with the process. The wrist or forearm is an ideal place as IV is put in there. My mum had blood transfusions and also had a stem cell transplant directly to her heart for cancer treatment and the tube went into the forearm. When I asked why, they said it was easier there to keep the needle and tube in place when you aren’t being monitored by the nurse every second of the transaction. I can attest to it being easier because I moved slightly when I coughed during a blood draw and after the procedure, I had a bruise about 2 inches squared or so that lasted 2 months maybe 2 and a half months. If you’re doing blood draws often, that’s bad. You won’t be able to see the veins you’re poking at. I don’t recommend anyone doing it themselves but for the sake of the story going that way, they are teaching the guy to do it all wrong, probably because the phlebotomist wants to do it himself to save everyone the hassle.

I appreciate the interesting discourse! I would like to say, however, that it is not impossible to obtain blood from the antecubital fossa, and in fact the most significant group of self-phlebotomists I'm aware of are in the anabolic steroid community, and they do this practice (inadvisably) when their hematocrit is elevated from the steroids. Also if you are a non-expert phlebotomist, I would say it is equally as challenging to even try and get the needle in your wrist or forearm due to the veins being more mobile and substantially smaller. In fact, I see a lot of severe bruising from forearm draws regardless of whether the individual coughs or not during the draw. It also takes a longer time to draw substantial amounts of blood from these areas due to flow. Additionally, it is not typically common to get blood draws from the legs due to risk of DVT, which can become serious and lead to pulmonary embolism and potentially death. In terms of placement of IV catheters, that is almost a separate discussion but they are placed in both the wrist and the antecubital fossa, and it should not be an issue to place it in the elbow because the IV catheter is flexible. Also, blood transfusions are different from blood draws in that the time needed for these span the order of hours rather than the shorter amount of time to obtain blood. Also, who do you think nurses turn to when they can't get a needle stick for a blood draw? --> a more experienced nurse --> doctor (with or without their handy dandy ultrasound machine)--> anesthesiology
But of course, this is all just a theoretical discussion in the name of good fun while we binge yaoi manga and by no means should you necessarily trust information from some rando on the Internet who claims to be a doctor

Yeah. I’m basing it off of my own knowledge of the human anatomy, forensics cases in the past, my own nurses and phlebotomists recounts and my own experiences. I’ve also had to inject myself a few times with depo shot which is stomach or thigh. I say thigh purely for the ease of location and it’s less chance of you messing up the angle if it’s right in front of you. As far as I’m aware, doctors aren’t advised to do blood draws as they aren’t practicing it often. Although they have knowledge of it and have done it before, they don’t do it on a daily basis and some of my own doctors have stated that they would rather attempt major surgery than a blood draw from how many years/decades it’s been since they last did one. This has been a very interesting discussion though!

That’s what I meant by “impossible”. I’ve struggled to do depo shots on myself and I know how to do them from being shown how to do it properly. To do a blood draw without being able to see the site in a mirror properly or see the veins properly, it would be too risky. Out of all of his options, it’s best just to be bit on the wrist and be done with it. Unless he’s used drugs via needles before, he’s just going to mess up and damage himself in the process.
You can’t get blood from your own elbow… it’s impossible to put the needle in properly yourself without absolutely destroying some veins going in and going out. I don’t know why the guy didn’t teach him how to safely draw blood HIMSELF cause all he did was do a standard blood draw as any nurse or phlebotomist would do.
This is by no means me telling anyone to do this or that it’s safe or that anyone should try this so keep that in mind!
But if you’re gonna do it yourself like this guy wants, do it in the leg or in the wrist. Wrist is easier, tourniquet under elbow and do is so tight that your arm goes very slightly numb. You need to properly cut off the blood circulation for a little while otherwise bad things can happen inside the vein. It’s better to do it up the arm than down is since the thicker “veins” called arteries take the blood to the appendages and the thinner ones (actually called “veins”) take the blood back to the heart. If you see a thin line that’s less than 1mm wide, it’s probably a capillary and you can’t draw blood from those. You can use butterfly needles which are thinner and have a higher chance of actually getting into the vein without any rupturing. While doing a blood draw, have sugar for the love of all that is holy and unholy in this universe. The last thing anyone needs is someone passed out while blood is still flowing out of them and into a blood bag or vials. Anyways I don’t think he will be able to handle using a needle to do blood draws. He’s actually better off cutting his wrist lightly since it’s actually not the best method to bleed out since there aren’t any major arteries in the wrist to bleed out quickly enough. It’s why vampires bite wrists when they just want a quick drink as opposed to draining a victim dry via carotid artery in the neck.
BTW, I’m not a serial killer or a doctor or anything. I want to be a forensic scientist so I know a lot of pretty weird and kinda morbid details about the human anatomy and a lot of things doctors know too. I just found this one part of the story to be extra nonsensical.