Blood collection tubes fill correctly during venipuncture due to which of the following factors?
The high pressure in the arterial system
The high pressure in the venous system
The positive pressure created by the tourniquet
The negative pressure within the tube
The Correct Answer is D
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A Reason:
Taking the specimen temperature before 4 minutes is the correct procedure according to the Department of Transportation (DOT) guidelines. The DOT Rule 49 CFR Part 40 Section 40.65 states that the temperature of the specimen must be checked no later than four minutes after the employee has given the specimen. The acceptable temperature range is 32–38 °C/90–100 °F, which helps to verify the validity of the specimen.
Choice B Reason:
Taking the specimen temperature at 5 minutes is not within the DOT guidelines. The temperature must be taken before 4 minutes have passed to ensure the specimen's integrity and to comply with the regulatory requirements.
Choice C Reason:
At 15 minutes, the temperature check would be too late. The DOT guidelines specify that the temperature should be checked no later than four minutes after collection to ensure the specimen has not been tampered with and is within the acceptable temperature range.
Choice D Reason:
After 30 minutes, the temperature of the urine specimen would not reflect the body temperature at the time of collection, which is necessary for the validity of the test. This delay could allow for the temperature to fall outside of the acceptable range, potentially invalidating the specimen.
Correct Answer is A
Explanation
Choice A reason:
The standard recommendation for fasting before a blood specimen collection is typically between 8 to 12 hours¹²³. This duration is considered sufficient to ensure that food intake does not affect the blood test results, such as glucose or lipid levels.
Choice B reason:
A fasting period of 1 to 2 hours is too short and would not provide an accurate representation of the body's baseline levels for most tests that require fasting. It is important for certain levels, like blood sugar and lipids, to stabilize, which takes longer than 1 to 2 hours.
Choice C reason:
Fasting for 4 to 6 hours may be appropriate for some tests, but it is not the standard fasting duration for most blood tests that require fasting. The shorter time might not allow for the clearance of lipids and glucose from the bloodstream that can influence the test outcomes.
Choice D reason:
A 24-hour fast is generally not required for routine fasting blood tests and could be potentially harmful, as it may lead to hypoglycemia, especially in diabetic patients or those with metabolic disorders. It is excessive for the purposes of standard blood tests.
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