Final answer:
The first drop of blood is wiped away to avoid contamination with tissue fluids, which can skew test results or the quality of a blood smear. This ensures more accurate medical diagnosis and treatment.
Step-by-step explanation:
When conducting a blood test or preparing a blood smear, it is common practice to wipe away the first drop of blood. This step is taken because the initial droplet may be contaminated with tissue fluids or interstitial fluids, which can affect the accuracy of test results or the quality of a blood smear. Ensuring that the blood sample is as pure as possible is critical in obtaining accurate diagnostic data. For instance, in a clinical setting, glucose or cholesterol readings might be skewed if tissue fluid is mixed with the blood. Moreover, when preparing a blood smear, a clean, unadulterated drop of blood is necessary to avoid a skewed distribution of cells.
Dogs, for example, have about 80-90 ml of blood per kg body weight, and even a small contamination in the sample, which can be as small as 10 μL, might lead to incorrect health assessments. Therefore, the practice of wiping the first drop ensures better reliability in medical diagnosis and treatment.