Why is the first drop of blood wiped after a dermal puncture?

Wiping away the first drop of blood after a dermal puncture is primarily done to absorb interstitial fluid, which can dilute the blood sample. Interstitial fluid is the fluid that surrounds the cells and tissues in the body, and it may contain substances that can interfere with the accuracy of certain laboratory tests. By removing the first drop, the lab assistant ensures that the sample collected afterward is more representative of the actual blood composition, leading to more reliable test results. This practice is critical for obtaining accurate measurements, especially in tests sensitive to the presence of contaminants from the dermis or the interstitial fluid.

While preventing contamination is also a valid concern, the specific reason for wiping the first drop focuses on the quality of the blood sample itself rather than preventing potential surface contaminants. Collecting more blood or reducing pain might be considered, but they do not address the primary rationale behind this procedure, which is to ensure that any interstitial fluid is removed from the collected sample.