People sometimes may also have hand lotions or other coatings on the skin that can affect blood glucose tests. I did several tests with OneTouch Ultra strips, using a new finger prick and new drop of blood each time, exposing the drop to air for about 5 seconds from prick to strip.
https://www.amazon.com/GenUltimate100-Strips-OneTouch-Ultra-Meters/dp/B00O9BU0VK

