The best method of monitoring response to insulin therapy is measurement of blood glucose concentrations. The vast majority of cats will allow blood collection if they are handled in the right way. Things that help with collecting blood from fractious cats are
- don’t make them wait
- do the collection in a quiet place such as a consulting room
- don’t let them see other cats or dogs
- consider the medial saphenous vein
- use the smallest amount of restraint possible
- use staff that like cats and involve the owner if possible
- if admitted for a blood glucose curve, try housing in a quiet separate location like a spare consult room or the office
- home glucose sampling by staff or owner
Most fractious cats are much better behaved with just their owners present, in a consulting room. I like to sample blood from the jugular vein with the help of the owner. I get owners to stand behind the cat and speak gently to them while petting their head. I slowly but firmly grab hold their heads by placing my thumb under their chin and fingers on top of their head and rotate upwards until vertical. Most cats have a 10 second window of opportunity so without releasing this grip, I use the other hand to shave the skin, swab with alcohol and then direct the owners index finger over the top of the vein and then collect blood using an insulin syringe. Having owners involved like this can be extremely daunting for many veterinarians but with confidence and competence, most fractious cats can have their blood sampled.
Stress induced hyperglycaemia occurs commonly in fractious cats making blood glucose taken under duress or from a stressed cat meaningless so don’t even bother if you have to pin a cat down with force.
Unfortunately, there are times when blood glucose sampling is simply not possible due to the temperament of the cat. What are we to do in such circumstances? Daily water drunk is often overlooked, but is an important tool for monitoring diabetic cats. Blood glucose concentrations above the renal threshold (14 - 16mmol/L in cats) result in glycosuria, osmotic diuresis, and compensatory polydipsia. Measurement of water consumption at home is simpler, cheaper, and less stressful to measure for the owner, cat and practitioner, and correlates better with mean daily glucose concentration than does fructosamine concentration.
Get the owner to start therapy at a dose of 0.25 units/kg of glargine s/c twice daily. Owners then measure the 24hr water intake and record it. Despite seeming obvious, owners must be instructed on how to accurately measure water intake. A measuring cup should be used to pour a known amount of water into the drinking bowl at the start of the period and then to measure it again at the end of the period. Access to alternate drinking sites must be removed and it may be necessary to confine the cat in part of the house if it drinks significantly from a source that can’t be measured, like a pond or swimming pool. Confinement will also be required in multi-pet households so as to be sure of the patients water intake.
Insulin dosage changes are then based on the water intake of the cat with the aim of keeping water intake to around 40mls/kg/day or 200mls per day for an average diabetic cat (normal daily water intake is 20mls/kg if fed wet food only and 70mls/kg if fed dry food only). Insulin dose can be increased weekly by 0.5-1U until water intake is at the desired level.
It is desirable, but not essential, to get pre-insulin blood glucoses in as many of these patients as possible. For some cats that cannot be handled in the clinic a housecall may be worth a try. A pre-insulin glucose of less than 10 mmol/L (on insulin glargine) should trigger a dose reduction.
Another useful tool to help is to get the owners to measure urinary glucose with a dipstick a couple of times a week. Diabetic cats should have some degree of glycosuria. A persistent negative urinary glucose should trigger a dose reduction whereas persistent 4+ urine glucose requires a dose increase. Owners can place paper based litters in a syringe and squeeze urine onto the dipstick with little impact on accuracy.
Management by measuring water intake will not work if there are concurrent factors causing polyuria, eg renal disease, drug therapy with frusemide. Diabetic cats can live many years and many eventually develop renal disease which then makes using water intake invalid for monitoring insulin therapy.
It is imperative to educate owners that this is not the best way of managing the disease and that the risks are increased and the quality of control is likely not as good. However, it provides a method of managing the fractious feline diabetic patient that is stress free to all involved. It can also be useful for those clients that lack the financial resources to manage their diabetic cat more intensively.