“This might sting a little.”

Those words, or a dozen variations on them, aren’t the most dreaded in medicine, but they can nonetheless evoke anxious feelings.

They are the last thing you hear just before a health-care worker slips a needle into your arm to give you medications or to withdraw blood for diagnostic tests or donation to a needy recipient. The technical name for the procedure is venipuncture [VEE-na-puncture]. It’s performed most often by nurses or by medical technicians known as phlebotomists.

In the vast majority of cases, hundreds of thousands of times a day, these medical procedures occur without incident. But very rarely, the “sting” turns out to be more than just a momentary discomfort. The needle can injure a blood vessel, a nerve or tendon, with lingering effects that may require follow-up medical attention.

How do you know when something’s amiss? One sign is if the anticipated sting turns out to be a sharp pain. If it does, then let the nurse know immediately, have the needle removed and seek follow-up care.

You should also be concerned if the puncture site continues to ooze blood after a few hours, if soreness persists, or if you experience numbness of the hand or fingers.

Short of an irrational fear of needles, concerns about the safety of venipuncture should never serve as an excuse not to donate blood. Collection personnel are normally well-trained and experienced. And the gift of blood is well worth the price of a momentary sting.