Where on a cat should one inject insulin?

Question

I've taken care of two diabetic cats (for different friends). One told me to inject the insulin in the fleshy part of a rear leg; the other told me to inject in or near the scruff of the neck (the same place I was taught by my vet to give subcutaneous fluids). Both friends were doing what their vets told them to do. In both cases, they gave the injections while the cat was eating. (I noticed that both cats stand to eat.) Both also said to vary the site slightly each time (don't keep hitting the same exact spot).

Are there important differences that would affect the choice of injection site, or does pretty much any place where there's enough room work and the two vets were just imparting personal preferences? The first cat had a very low dose (1.5 units) and the second a higher dose (5 units), but both of those seem pretty insignificant in terms of pushing liquid into the cat.

Answer 1

I suspect that the recommendation to inject in the leg was made out of an abundance of caution to avoid injection site sarcoma (ISS), while the recommendation to inject in the scruff was made from a combination of factors:

• It's the easiest site for an owner to give an injection
• There's no proof that insulin can cause ISS
• Some vets still aren't aware of ISS

What Is Injection Site Sarcoma?

ISS, previously called Vaccine Associated Sarcoma (VAS) is a particularly invasive form of cancer that is believed to form at any injection site that may have some inflammation (Woodward 2011). However, the only proven causes of ISS are prior administration of killed, adjuvanted rabies or leukemia vaccine (Wilcock 2012).

Adjuvanted vaccines have an ingredient that increases the inflammation (to force an immune response to the disease ingredients in the vaccine), and it is believed that that inflammation plays a key role in the development of sarcomas. Adjuvanted vaccines should be avoided for that reason.

The second recommendation can be applied to all injections, and that is that injection sites should be located in an area where if a sarcoma develops, it can easily be removed. That is generally recommended to be the leg (which can be amputated if a sarcoma develops), but I spoke to a vet tech earlier this year who works with an oncologist who recommends the stomach because the chest wall is easy to remove the sarcoma from.

For any injection, I generally weigh the risk of developing an ISS against whatever illness I'm treating. When my cats got a steroid shot for itch relief while the flea medication killed the cheyletiella mites, I requested it in their legs just to be safe. If I was giving fluids to a cat in renal failure, I would not worry about the chance of developing cancer in a few years.

References

Kevin N. Woodward ISRN Veterinary ScienceVolume 2011 (2011), Article ID 210982, Origins of Injection-Site Sarcomas in Cats: The Possible Role of Chronic Inflammation—A Review web abstract

Brian Wilcock, Anne Wilcock, and Katherine Bottoms Can Vet J. Apr 2012; 53(4): 430–434. Feline postvaccinal sarcoma: 20 years later web abstract

Answer 2

My parents have a diabetic cat, and they tend to prefer the scruff of the neck - they have used other sites but the scruff seems to be the easiest to access. From what they were told, you just need to make sure there is enough room for the fluid.

The scruff just tends to be an easy site, as if the cat is eating or holding still and sitting (my parents cat will just come and sit when the alarm goes off for his injection and the epileptic cat's daily pill), its really easy to reach, and also gives you more space to needle without risking injury (if you go too deep/hard, etc).