A phlebotomist should identify that a blood spot collection for inborn errors of metabolism requires which of the following?
The newborn must be at least 3 days old.
The circles on the filter paper must be at least half filled.
The first drop of blood immediately following the puncture must be included.
The specimen must be completely dried before the test can be processed.
The Correct Answer is D
Choice A Reason:
The age of the newborn is important for certain metabolic screenings, as some metabolites may not be present or at measurable levels immediately after birth. However, the requirement for the newborn to be at least 3 days old is not a standard for all blood spot collections for inborn errors of metabolism (IEM). Some screenings are performed within 24 to 48 hours after birth.
Choice B Reason:
While it is important that the circles on the filter paper are adequately filled to ensure there is enough blood for the test, the requirement for them to be at least half filled is not specified in the guidelines. The focus is usually on ensuring the blood spot is of the right size and properly saturated through the filter paper.
Choice C Reason:
The inclusion of the first drop of blood is not typically a requirement. In fact, the first drop is often wiped away to avoid contamination with tissue fluids that could affect the test results. Subsequent drops are used to fill the circles on the filter paper.
Choice D Reason:
The specimen must be completely dried before the test can be processed to prevent degradation or hemolysis of the blood sample. This is a critical step in the preparation of the sample for accurate testing of IEM. The drying process helps preserve the integrity of the metabolites to be analyzed.
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Related Questions
Correct Answer is B
Explanation
Choice A reason:
The order of citrate, heparin, EDTA, and fluoride is not the correct sequence for blood collection. The correct order is essential to prevent cross-contamination of additives between tubes, which could interfere with test results. Citrate tubes should be drawn first to ensure that the blood does not clot prematurely, but heparin should not follow immediately after citrate.
Choice B reason:
Citrate tubes, which contain sodium citrate, are used for coagulation tests and must be drawn first to ensure the proper blood-to-additive ratio. EDTA tubes are drawn next because EDTA binds calcium and prevents clotting, making it ideal for complete blood counts and other hematology studies. Heparin tubes, which prevent clotting by inhibiting thrombin and thromboplastin, are drawn after EDTA. Lastly, fluoride tubes, which contain a glycolysis inhibitor, are drawn to preserve glucose levels and are typically used for glucose and lactate testing.
Choice C reason:
Starting with fluoride is not recommended as it could lead to contamination of the EDTA and heparin tubes with fluoride, which could affect the results of certain tests, such as calcium determinations in heparin tubes. The order of draw is designed to minimize such risks.
Choice D reason:
This sequence is incorrect because fluoride tubes are not drawn before EDTA and heparin tubes. The presence of fluoride could potentially contaminate the subsequent tubes and alter the results of the tests that require heparin or EDTA as an anticoagulant.
In phlebotomy, following the correct order of draw is crucial. The order is established based on the type of additive in each tube and its potential to interfere with tests conducted in subsequent tubes. The standard order is: blood cultures, citrate tubes, serum tubes with or without clot activator and gel, heparin tubes with or without gel, EDTA tubes, and lastly, fluoride tubes. This sequence helps prevent cross-contamination and ensures the accuracy of laboratory results, which are critical for patient diagnosis and treatment.
Correct Answer is D
Explanation
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.
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