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Checking for colour and Capillary Refill Time (CRT)

Explore how to check for colour and Capillary Refill Time (CRT) as part of checking an animal's vital signs.
Image of a vet checking a dog’s gum colour.


An animal should always have a fresh, healthy pink colour in their mucous membranes (most often checked at the gums in dogs and cats or the gums or nostrils in horses, though other areas can be used).

While there are many causes of pallor (pale colour), they generally fit into one of three categories:

  • Excessive blood loss: If there are no obvious external bleeding wounds, internal bleeding should always be considered as a possibility. This could be following a trauma such as a car accident where an internal organ has been injured and is bleeding, following a surgical procedure such as a spay, or a ruptured spleen is not an uncommon cause of internal bleeding. Toxicities such as rat bait ingestion can also cause bleeding . Some diseases over time can cause blood loss chronically, such as intestinal or renal loss of blood cells. A slow internally bleeding tumour is also a possibility.
  • Insufficient blood production: This can be due to the insufficiency of various organ systems including the spleen, the kidneys or the bone marrow, or it can be due to insufficient products required to make blood cells such as iron.
  • Inability to get blood around the body: Sometimes the body might have the right amount of blood, it just isn’t getting to the surface properly and therefore the gums look pale. Primary issues with the heart or lungs, low blood pressure as well acute conditions such as shock, can cause an animal to be pale as the body prioritises sending blood to the vital organs instead of the peripheral vessels. Dehydration will also mean that the body isn’t getting the fluid in the vessels sufficiently around the body so a dehydrated animal might have pale gums.

Darker than usual gum colour can be due to excessive excitement or stress, hyperthermia, toxicities or shock. Also take note of less common mucous membrane colours, such as having a yellow tinge (which could indicate liver issues), a blue tinge (which could indicate breathing difficulties) or a muddy brown colour (which could indicate shock).

While checking gums, also take note of any bruises or pinprick spots in the mucous membranes which can be indicative of coagulation disorders and are usually an emergency.

Capillary Refill Time (CRT)

See Rehabilitation of Domestic Animals Module for more information on taking the CRT.

A slow CRT (above 3 seconds) indicates that an animal isn’t getting appropriate perfusion to all their tissues. This can be due to primary cardiac or vascular issues, shock, hypothermia or dehydration.

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Basic First Aid for Animals and Pets

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