Dog drinking a lot of water and peeing: what the blood test looks for

Put a number on it before the appointment

Drinking a lot is a feeling until it is measured, and the measurement is the one piece of information you can produce that the practice cannot. Over 24 hours, an adult dog on dry food usually drinks something under roughly 60 to 70 ml of water per kilogram of body weight. An intake above 100 ml per kilogram per day is what vets generally treat as true excess. For a 20 kg dog, that threshold works out at about 2 litres in a day.

How to measure it with a kitchen jug and nothing else:

• Fill every bowl in the house with a measured amount and write the figure down.
• Top up only with measured amounts, noting each one.
• At the same time next day, measure what is left and subtract it from the total poured.
• Count every water source: the second bowl upstairs, the bucket in the garden, the pond, the toilet. If one of them cannot be controlled, say so rather than guessing.
• In a household with more than one animal, separate them for the measurement or the number means nothing.
• Note the food type. Wet food is roughly three quarters water, so a dog moved from wet to dry will drink visibly more from the bowl with nothing wrong at all.
• Repeat over two or three ordinary days, not on a heatwave day or the day after a long walk.

Weigh the dog on the same day. Intake only means something per kilogram.

Drinking more and passing more travel together

The two signs are two halves of one mechanism, and which one came first matters. Either the dog is losing water it cannot hold on to and drinks to keep up, or it is drinking for another reason and passes the surplus. Most of the conditions below work the first way, which is why the urine sample carries as much weight as the blood sample.

Details worth writing down: accidents indoors in a dog that has been clean for years, waking in the night to drink or to be let out, urine that has become much paler, a bitch that is unneutered and has been in season in the past two months, any current medication, and whether the appetite and the weight have moved.

The three lines of enquiry a vet opens first

Other lines the same panel helps with: a womb infection in an unneutered bitch, which is a surgical emergency, a liver problem, a raised blood calcium, a high blood sodium, and the much rarer failure of the hormone that concentrates urine. Medication is checked first of all, because steroids and diuretics produce the same picture on purpose.

What each line on the report contributes

• Urine specific gravity. The most direct reading of whether the kidney can still concentrate. Collect a sample first thing in the morning, in a clean container, before the appointment and before any fluids are given. A dilute sample alongside a raised creatinine points towards the kidney itself, a well concentrated one points elsewhere.
• Creatinine. Waste from muscle, cleared by the kidney. It only rises clearly once a large share of filtering capacity has gone, so a value inside the range does not clear the kidney on its own.
• SDMA. Cleared by the kidney as well, but it leaves the range earlier than creatinine and is barely affected by how much muscle the dog carries. In a thin older dog it is the more honest of the two.
• Urea. Rises with reduced filtration, but also with dehydration, a protein rich meal shortly before the sample, or bleeding in the gut. High urea with a normal creatinine usually has nothing to do with the kidney.
• Blood glucose. Diabetes shows as a level that is high and stays high, with glucose appearing in the urine once the kidney's threshold is passed, around 10 to 12 mmol per litre in dogs. A mildly raised single reading in a stressed dog is not the same finding.
• Alkaline phosphatase. Raised in most dogs with Cushing's disease, but also raised by steroid treatment, by bone growth in a young dog and by a long list of liver and bile duct problems. It opens a question, it never closes one.

Two habits of reading. Compare a value only with the range printed on your own report, because ranges differ between analysers and laboratories. And remember that one sample freezes one moment, so a repeat under similar conditions is often what settles the matter. Cushing's disease in particular is never confirmed on a routine panel: it needs a dedicated hormone test that your vet will discuss.

Questions to ask your vet

1. Here is the measured 24 hour intake in ml per kilogram. Does it put my dog above the threshold you use?
2. Was a urine sample collected before any fluids, and what was the specific gravity?
3. Do creatinine, SDMA and urea move together, or is only one of them out of range?
4. Was glucose found in the urine as well as in the blood?
5. Is the alkaline phosphatase explained by anything already known, such as a medicine or my dog's age?
6. What would the next step be, and is a repeat sample needed before deciding anything?

Why is my dog drinking excessively all of a sudden?

A sudden change is more informative than the absolute amount. Hot weather, a switch from wet to dry food, more exercise, a course of steroids or a diuretic all increase drinking for reasons that are not illness. Once those are excluded, the common medical reasons are a kidney that can no longer concentrate urine, diabetes, raised cortisol, a womb infection in an unneutered bitch, a liver problem or a raised blood calcium. None of these can be told apart from the bowl alone, which is why the test exists.

My dog is drinking a lot of water but acting normal. Does that still need a blood test?

Yes, and that is the usual picture. Dogs stay bright and keep eating well through the early part of most of these conditions, because the body compensates by drinking more. A normal demeanour tells you the situation is not an emergency tonight, it does not tell you the panel will be normal. Book the appointment, take the measured intake and a morning urine sample with you.

My dog is drinking a lot of water at night. Does the timing mean anything?

Timing is worth reporting but it does not point to one cause. What matters more is whether the dog now wakes you to go out, asks to be let out more often in the day, has started having accidents indoors after years of being clean, or passes urine that looks much paler than it used to. Those four details are what the vet will ask about, so write down what you have seen before you go.

What does specific gravity in dog urine mean?

It measures how concentrated the urine is, which is the most direct reading there is of whether the kidney can still pull water back. In a dog, a well concentrated sample usually sits above about 1.030, while a value in the 1.008 to 1.012 band means the kidney is neither concentrating nor diluting. Read next to a raised creatinine, dilute urine and concentrated urine point in very different directions, so the sample needs to be collected before any fluids are given.

How much water is too much for a dog?

Vets generally treat an intake above 100 ml per kilogram of body weight per day as genuinely excessive, against a usual figure under roughly 60 to 70 ml per kilogram for an adult dog on dry food. For a 20 kg dog that threshold is about 2 litres in 24 hours. A dog on wet food drinks far less from the bowl because its food is mostly water, so the type of diet has to be stated alongside the figure.