Which common test requires the lavender tube to be filled to the top?

The erythrocyte sedimentation rate (ESR) test requires the lavender tube to be filled to the top to ensure accurate results. This test measures the rate at which red blood cells settle at the bottom of a tube over a specified period. When the tube is filled properly, it ensures that the correct volume of blood is mixed with the anticoagulant present in the lavender tube, which typically contains EDTA. Proper filling is crucial because an incorrect blood-to-anticoagulant ratio can lead to erroneous test results. This is particularly important in the ESR test, where precise relationships between components can impact sedimentation rates and thus the accuracy of the test.

Other tests listed may have different requirements in terms of tube volume or may use different additives for their respective analyses. However, the ESR specifically emphasizes the importance of complete filling to maintain the integrity and reliability of the test results.