ELI5: How can you run out of blood during a blood test?

r/

Hey just curious cos I’m completely stumped about this.
I went to get blood drawn and ran out after 1.25 vials??

The needle was wiggled around but the nurse couldn’t get more and I promptly felt like I was going to past out.

I saw online that it can be from lack of water + other factors but this still confuses me

How is this possible in the first place, are bodies just not continuously pumping more ?

Comments

  1. zorba1 Avatar

    Your body didn’t run out of blood. Your body was reacting negatively to being poked and prodded, the initial poke wasn’t quite right so blood wasn’t flowing well, and the tech or nurse didn’t want to try again and risk you passing out or worse.

  2. Ok-Vacation-8109 Avatar

    You didn’t run out of blood. There could have been an issue with the positioning of the needle, the vein could have collapsed, etc. there was just a problem with blood flow. The human body has over a gallon of blood in it.

  3. Choobot Avatar

    Sometimes the tip of the needle pulls out of the vein or pokes through the other side. (It sounds awful, but it’s less damaging than you think; your vein isn’t going to get torn in half or anything, they’re extremely strong, stretchy mf’ers that patch themselves up fairly quick).

  4. steelcryo Avatar

    Not a doctor, so might be wrong, but from what I know there’s lots of reason for the blood to stop flowing.

    Things like dehydration or low blood pressure can affect how fast your blood flows and depending on the size of the vein, hydration, blood pressure etc. The vein can sometimes collapse which is more likely if you’ve got weak or small veins too.

    Your blood also clots around the hole in the needle and can block anymore from flowing. Sometimes wiggling it around can help dislodge the blockage. Or if the needles not quite in the right place, wiggling can free the tip if its against the vein wall.

    I’ve had it before where they just swapped to a new needle and it was fine, but if you started feeling dizzy, they probably decided they’d got enough and didn’t want to make you feel worse.

  5. FriedBreakfast Avatar

    Well, you can’t run out of blood, otherwise you die.

    The needle didn’t pull any more blood from that spot. A number of reasons could be possible. It’s possible the needle moved to a spot where blood wasn’t flowing. The blood vessel could have closed off ( happens when people bleed out ) . Blood could have clotted around the needle opening. It’s hard to say exactly what happened

  6. superduperzz Avatar

    Most likely this is due to the skill and technique of the phlebotomist. You definitely did not run out of blood after a vial or 2 was drawn. Some people, including myself, are hard sticks and require more patience to have blood drawn from.

  7. DrSuprane Avatar

    The vein ran out of blood which happens. Those tubes have a vacuum so it sucks the blood out. The walls of the vein can collapse as the blood is removed.

    They like to stick the vein near the elbow because the veins are larger (more blood), it’s easier to put the needle in and there are limited valves in that area. Small veins have less blood than large veins.

  8. rosen380 Avatar

    A good person to ask would have been the nurse that was with you when it was happening…