High blood glucose in cats: stress before diabetes

What this marker measures

Blood glucose is the amount of glucose present in the blood at the precise moment the needle goes in. It is a snapshot, not an average. Glucose is the fuel for cells, and its level is held within a narrow band by several hormones, among them insulin, which moves it into the cells.

Cats have one feature that changes how the result reads. Under the effect of fear, restraint, travel or pain, they release adrenaline and cortisol, which push blood glucose up within minutes and sometimes substantially. That rise can reach levels overlapping those seen with diabetes. It is real in biological terms, but it does not reflect a disease of sugar handling.

What vets look into when the value sits outside the range

By frequency, in the setting of a consultation:

• Stress hyperglycaemia. The first reason a cat is wrongly flagged for diabetes, especially an animal that dislikes travel or the practice.
• Diabetes mellitus. Common in middle-aged to older cats, more so with excess weight and an inactive life.
• A recent meal. The effect stays modest in cats, but it counts when the value only just clears the range.
• Medicines. Corticosteroids in every form, progestogens, fluids containing glucose.
• Severe acute illness, intense pain, pancreatitis.
• Advanced kidney disease or hyperthyroidism, which usually come with other abnormalities on the panel.
• Underlying hormonal disease, including excess growth hormone, called acromegaly, a cause of feline diabetes more frequent than was long thought, and hyperadrenocorticism.

Feline diabetes is not accepted on a single sample. It requires a high glucose that lasts, found on several measurements or confirmed by fructosamine, together with consistent signs seen at home. A cat that drinks more, passes more urine, eats more and still loses weight draws a picture that the biology then confirms, not the other way round.

What this value does not tell you on its own

A one-off high glucose establishes nothing by itself in a cat. What goes around it:

• Fructosamine. This is the arbiter. It reflects the average of the last one to three weeks and does not move with the stress of the day. A high glucose with a fructosamine inside the range points to a one-off rise; both raised together carry real weight.
• The urine dipstick, with two separate pieces of information: glucose and ketones. The presence of ketones changes how urgent the situation is.
• What you see at home, which counts as much as the biology: how much water is drunk, a heavier litter tray or one changed more often, a bigger appetite with weight loss, a dull coat, a gait that sinks at the back.
• Weight followed over time, compared with earlier weigh-ins.
• The rest of the panel: kidneys, liver, thyroid, pancreas, electrolytes.
• A series of measurements, taken at home where that is possible, which gives a far truer picture than a single point at the practice.

One last practical point. The range printed on your report depends on the laboratory, the analyser and sometimes the type of device used. A handheld glucose meter and a laboratory analyser do not give exactly the same figures. Always compare measurements made with the same equipment.

Questions to ask your vet

1. Has a fructosamine been done, or is it indicated before we conclude anything?
2. Has the urine been analysed, looking for glucose and for ketones?
3. Is my cat given anything that could raise blood glucose, corticosteroids and progestogens included?
4. Can we arrange measurements at home, and how exactly do I go about it?
5. If diabetes is confirmed, will you look for an associated hormonal cause such as acromegaly?

My cat has sugar in the blood and in the urine, does that have to be diabetes?

No. In cats, a stress rise that is marked enough and lasts long enough can push glucose into the urine. The vet cross-checks with fructosamine, with the signs seen at home and with the weight trend before concluding.

What exactly is fructosamine?

It reflects the average blood glucose over the previous one to three weeks, measured on blood proteins bound to glucose. It does not move with the emotion of the day, which makes it the arbiter between a one-off rise and an established high glucose. It can be misleading in some situations, notably with hyperthyroidism or low blood proteins.

How do I limit stress at the blood test?

Get the cat used to its carrier in advance, cover the carrier on the journey, avoid a long wait in the waiting room and ask for short handling. Some practices offer a cat-friendly consultation. A measurement taken at home, where that is possible, partly gets round the problem.

Can a cat on corticosteroids have a high blood glucose?

Yes, corticosteroids and some progestogens raise blood glucose in cats. Report any product given, including injections and topical products, and do not stop or change anything without the advice of the vet looking after your cat.