A phlebotomist should explain the procedure prior to venipuncture to:

Choice A reason:
The high pressure in the arterial system is not a factor in the filling of blood collection tubes during venipuncture. Arterial blood is not typically collected using evacuated tubes; these are used for venous blood collection, where the pressure is lower.

Choice B reason:
While the venous system does have pressure that aids in blood flow, it is not the high pressure that causes blood collection tubes to fill. Venous pressure is relatively low compared to arterial pressure, and on its own, it is not sufficient to fill the vacuum tubes used in venipuncture.

Choice C reason:
The positive pressure created by the tourniquet can help engorge the veins, making them easier to access, but it does not directly cause the blood collection tubes to fill. The tourniquet's role is to assist in vein visualization and palpation rather than in the filling of the tube.

Choice D reason:
The negative pressure within the tube is the correct factor that causes blood collection tubes to fill during venipuncture. When the needle punctures the patient's vein and then the tube stopper, the vacuum in the tube pulls blood into it until the vacuum is exhausted or the tube is filled. This is why it is essential not to allow the tube contents to contact the stopper, as backflow into the venous system can cause adverse reactions.

Choice A Reason:
The patient's condition is a critical factor as it can influence the ease of blood collection and the choice of collection site. For example, a dehydrated patient may have less accessible veins. Patient age is also important; pediatric and geriatric patients may require different approaches due to vein size and fragility. The blood volume required for testing must be considered to ensure sufficient sample size without compromising patient safety, adhering to guidelines that limit blood collection to a certain percentage of the patient's total blood volume.

Choice B Reason:
While patient height and gender may influence the choice of blood collection site, they are not as critical as the factors listed in choice A. Patient medications are important to consider, as some medications may affect coagulation or the integrity of the sample.

Choice C Reason:
The ordering physician's preferences may be considered, but they are not a primary factor in the method of collection. The number of tests ordered and the diagnosis can influence the volume of blood needed but are secondary to the patient's condition and safety considerations.

Choice D Reason:
The time of day and the timing of the specimen collection can be important for certain tests that are time-sensitive or influenced by diurnal variations. The test status, whether routine or stat, may affect the urgency of collection but not necessarily the method of collection.