Why is the first drop of blood wiped away during capillary punctures?

Wiping away the first drop of blood during capillary punctures is essential primarily because it contains high levels of tissue fluid. When blood is drawn from a capillary site, the first drop can be contaminated with interstitial or tissue fluid, which can dilute the blood sample and alter the test results. This dilution can lead to inaccurate measurements of analytes, particularly for tests that require precise concentrations, such as glucose or hemoglobin levels.

The practice of discarding the first drop ensures that the sample collected reflects a more accurate representation of the blood's composition, free from the potential contamination of tissue fluid that may interfere with diagnostic tests. Ensuring the integrity and accuracy of the blood sample is crucial in providing reliable diagnostic information.