Drinking more, weighing less: early CKD changes you can see at home (not a diagnosis)

Healthy kidneys concentrate urine to conserve water. As function declines, concentrating ability falls, urine volume rises (polyuria), and the animal drinks more to compensate (polydipsia). Cornell describes this as a common early sequence: larger urine volumes and increased water intake.[1]

The International Renal Interest Society (IRIS) lists loss of concentrating ability — after other causes of polyuria/polydipsia are excluded — as a clue to renal abnormality. Persistent urine specific gravity below 1.035 in a cat, especially on a dry diet, may indicate a renal problem.[4] A bowl that empties faster is a reason for veterinary testing, not a label you assign at home.

ISFM consensus guidelines likewise list polyuria/polydipsia and weight loss among findings that justify further investigation, and note that early CKD can show few overt signs.[3][5]

In a 2016 Journal of Veterinary Internal Medicine study, Freeman and colleagues reviewed 569 staged CKD cats from six U.S. practices. Median weight loss was 8.9% in the 12 months before diagnosis; curve analysis suggested loss could begin three years earlier and accelerated after diagnosis. Cats weighing under 4.2 kg at diagnosis had significantly shorter survival.[6]

That is not “8.9% loss equals CKD.” The paper describes weight trajectories in cats who already had a diagnosis. The clinical point is that serial weights on the same scale may help a veterinarian notice a change that warrants testing.[6] ISFM also recommends routine nutritional assessment — diet history, body weight, body and muscle condition — in older cats.[3]

Useful notes are concrete: whether the same bowl empties faster, whether litter or outdoor urine volume has clearly increased, weekly weight at a consistent time, and a rough appetite fraction. That gives a veterinarian a timeline instead of “they seem off.”

IRIS is explicit: staging happens after CKD has been diagnosed in a relatively stable patient, using fasting creatinine and/or SDMA, then substaging by proteinuria and blood pressure.[4][7] The diagnosis itself is a clinical synthesis that includes blood and urine — not water intake alone.[4][5][7]