A capillary refill test is a medical diagnostic test. A medical professional observes how long it takes blood to return to the fingernail bed after pressure has been placed on the fingernail for a period of time.
According to the National Institute of Health, this test is used to diagnose certain medical conditions, such as dehydration and restricted blood flow. Health Central states that in a patient with good blood flow and proper hydration, the pink color returns to the nail bed within two seconds. If it takes longer than this for the color to return, further testing may be necessary.