What does capillary refill time (CRT) measure in an animal?

Capillary refill time (CRT) is an important clinical indicator used to assess perfusion status in an animal. It measures how quickly blood returns to the capillaries after they have been compressed, typically by applying pressure to the mucous membranes, such as the gums. When pressure is released, the time it takes for the color to return to the area indicates how well the blood is circulating through the capillaries and, by extension, the overall perfusion status of the animal's tissues.

If CRT is prolonged, it may suggest issues such as poor blood circulation, shock, or dehydration, indicating that the animal may not be adequately perfusing its tissues. A normal CRT, on the other hand, usually indicates that the animal has adequate blood flow and perfusion.

While other factors like oxygen saturation, blood volume, and hydration level are also important for assessing an animal's health, they are not directly measured by CRT. For example, oxygen saturation refers to the percentage of hemoglobin binding sites in the blood occupied by oxygen, which is assessed using pulse oximetry, while blood volume relates to the total amount of blood in circulation, and hydration level indicates the fluid balance within the body, both of which would require different assessments.