Why do they do this during the hemoglobin test when I donate blood?

When I donate blood, there’s always finger stick for a hemoglobin test first. When the phlebotomist does this, he/she pricks my finger, squeezes out a drop of blood, wipes it off, squeezes out another drop, then loads that one into the hemoglobin-tester. Why not take the first drop? Why is the second one better?

The first drop of blood is often diluted with tissue fluids (skin oils pushed into the new puncture, etc.) that can alter the result of the test. Wiping off the first drop removes the skin oils that have been pushed into the wound, so when the second drop comes out it’s just good ol’ blood.

ETA: It’s recommended that diabetics do the same thing with finger prick tests for blood glucose, and it’s for the same reason – dilution of the blood will always throw off the results.

Which leads to another question - why do they do the hemoglobin test first? Why not ask all the disqualifying questions beforehand, so you don’t waste a test kit & risk a pissed off deferred donor who had an unnecessary blood stick done? I asked the tech last time I gave blood, but she couldn’t explain it beyond “That’s the order we’re instructed to do it in.”

:confused: I always fill out the forms and do the interview before I get pricked.

I would guess that it’s because the hematocrit is more likely to result in a deferral. Most people who aren’t eligible for one of the reasons on the questionaire will never go in to donate in the first place (it’s kind of hard to not know whether you’re a male who has ever, even once, had sex with another male since 1977), but a person might meet all of the lifestyle requirements but be near the borderline on the hematocrit requirement. Yeah, it’d be annoying to have your finger pricked and then be turned away because of the questionaire, but it’d also be annoying to spend five minutes answering personal questions and then be turned away because your blood drop floats in copper sulfate.

When I worked there we did the procedures more or less simultaneously. Donors read a card with the obvious questions on it while they were waiting to be checked in. Then there was a more detailed verbal questionnaire while the haemo was done. A marginal result in the copper sulphate would normally (with the donor’s consent, of course) be repeated using a second sample in a haemoglobinometer - a word that I must surely have spelled wrong.

But the most common reasons for deferral were use of aspirin/paracetamol/ibuprofen in the last 24 hours and failed haemo, so I suspect Chronos has the answer.

They used to ask me all the questions, then do the test, then my blood wouldn’t drop, then they would have to spin it (which takes time), and then they’d tell me whether or not I could donate that day.

I would ask for the blood test first, so that if they needed to spin it, the spinning would happen while they were doing blood pressure, temperature, and “have you ever…” questions and that way the blood spinning was nearly done and there was less wait time.

Maybe different Red Cross branches use different protocols then? When I went last week, all I was given ahead of time was a list of medications that would defer me. This was followed by the interview with a tech who started with the finger stick, then all the normal questions (various meds, various diseases, travel, sexual habits). While most of them were of the permanent deferral type, a few were transient enough (aspirin in the last 48 hours, etc.) that would have been nice to get out of the way before driving any steel into my precious skin.

I donate at Delta Blood Bank. There it’s fill in the questions first, then review of the questions with expansions on the answers. After that comes the blood pressure, temp, and finger stick.

So I guess it’s different procedures for different centers.

In this area, Puget Sound Blood Center is where blood is donated, not the Red Cross.

In the New York City region, blood collection is handled by New York Blood Services, also not by the Red Cross.

Today, I attempted to donate platelets, but was turned down because my hemoglobin was too low. (At a blood drive last week, a woman from the blood center recruiting platelet donors told me that platelet donation didn’t affect your hemoglobin, and you can donate them three days after donating whole blood, so I signed up. I was rather pissed when the guy pulled out the hemoglobin-testing machine, as I’d just traveled a good ways to get to the donor center.) Anyway, I offered my left hand for the ultimately damning finger-stick, but the phlebotomist asked for my ‘writing hand,’ which is my right. I expressed surprise, and he repeated the question, then asked if it was a problem, which it isn’t, really, although I prefer them to attack my left. Why would he do this? Is there a reason why my hemoglobin levels would be different in my dominant hand vs. my weaker hand?

Good for you for trying! I’m told that the FDA won’t allow you to donate platelets within 8 weeks of having donated whole blood. The reason for that is that some whole blood is lost in the pheresis kit, and for testing, platelet counts, etc.

I’ve failed the hemoglobin test a couple of times, and it’s usually because some newb squeezed the finger too much during the finger prick and got a bunch of lymph tissue, which dilutes the blood. They’ve never cared which hand I give them to prick, though. :confused:

I donate every three weeks (tomorrow is my day) and I encourage you to try again to donate. They need you!

Probably not, no, but it may be easier to get a sample from your dominant hand.