If a patient reports a history of episodes of syncope, the most appropriate response is to place the patient in a recumbent position, either lying flat or reclining in a chair, so that he or she does not fall or experience injury if an episode of syncope occurs. Syncope is fainting that occurs with a sudden drop in blood pressure, and is sometimes associated with stress or fear. Patients who are fearful of needles or the sight of blood are especially at risk for syncope during venipuncture.

The most common reason for rejecting a specimen for chemistry is hemolysis, whereas the most common reason for rejecting a specimen for hematology is clotting. Other reasons that specimens may be rejected include overfilling or underfilling a tube, because this alters the required ratio of additive to specimen and can interfere with the testing results. Specimens transported and handled in the wrong collection tube, at the wrong temperature, with the wrong additive, or with exposure to light (if photosensitive) may also be rejected.

If a patient has made a fist for venipuncture, the point at which he or she should generally be instructed to open the hand is when blood flow is established. The purpose of making a fist is to increase the pressure in the veins and thus their visibility. The patient should be cautioned to avoid pumping the fist, which can increase potassium levels. The hand may remain clenched during collection if the vein appears that it may collapse if the fist is unclenched.

During capillary blood collection, the first drop of blood should be wiped away, as it may be contaminated with tissue fluid or may contain alcohol residue that may hemolyze the specimen or prevent blood from forming a well-rounded drop. Using strong repetitive pressure to "milk" the site may result in hemolysis or tissue fluid contamination. Using a scooping motion against the skin surface may cause platelet clumping or hemolysis. Removing the tube from the site may create air spaces in the specimen that interfere with test results.

If an accidental arterial puncture is suspected, the correct response is to withdraw the needle immediately and apply strong pressure for a minimum of 5 minutes, observing the site carefully for signs of swelling or bleeding. The ordering physician must be notified, and an incident report mustbe completed. If a specimen was already collected before an arterial puncture was suspected, the laboratory may still be able to test the arterial blood.