Which of the following tests has a fasting requirement?

Choice A reason:
The light green tube typically contains lithium heparin and is used for plasma determinations in chemistry. It is not suitable for coagulation studies, such as PT, because heparin is an anticoagulant that would interfere with the test results.

Choice B reason:
The lavender tube contains EDTA, which is an anticoagulant that binds calcium. While it is commonly used for complete blood counts (CBC) and other hematology tests, it is not appropriate for coagulation studies because the binding of calcium would affect the clotting process required for a PT test.

Choice C reason:
The royal blue tube can come with different additives or be additive-free, depending on the color of the closure. It is primarily used for trace element testing, toxicology, and nutrient determinations. The additives in a royal blue tube could potentially contaminate the sample and interfere with the PT test.

Choice D reason:
The light blue tube contains sodium citrate, which is the appropriate anticoagulant for coagulation studies like PT. Sodium citrate works by binding calcium in the blood, preventing clotting. The PT test measures the time it takes for a clot to form after re-calcification, making the light blue tube the correct choice for this test.

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.