SYMPTOM
Frequent unproductive litter tray visits
A cat goes in and out of the litter tray repeatedly, squats or strains for long periods, and leaves little or no urine behind. Some cats cry out, lick at the genital area, or pass small drops of urine, sometimes blood-tinged, in the tray or elsewhere in the house. Because the posture looks similar, owners often take it for constipation. In the litter itself, the difference between several small clumps and no clumps at all is one of the few clues visible at home, but it is an imperfect one: a partly blocked male cat can still pass a few drops, so small spots of urine do not rule out a blockage.
Urethral Obstruction
Crystals, mucus plugs, or small stones can partially or fully block the urethra, preventing urine from leaving a bladder that continues to fill. Obstruction occurs almost exclusively in male cats, whose urethra is considerably narrower and longer than a female's. The cat repeatedly postures in the tray, often vocalising, while passing little or no urine. Obstruction most often follows idiopathic cystitis, and less often stones. Once urine cannot leave, potassium and waste products build up in the blood: kidney values can rise within 24 to 48 hours, a high potassium level can slow the heart into a fatal rhythm, and death can follow within about three days if the blockage is not relieved. Vomiting, hiding, weakness and collapse tend to appear as this develops. In a UK study of 1,108 obstructed male cats under primary veterinary care (Beeston and colleagues, 2022), 329 (about three in ten) died or were euthanised during an obstruction episode, and about three-quarters of those deaths came within 48 hours of diagnosis. Whether the bladder is overfull and hard, and whether the urethra is fully blocked, cannot be judged at home.
Feline Idiopathic Cystitis
Inflammation of the bladder wall without infection or stones is the most frequently identified cause of lower urinary tract signs in cats under ten years old. It is associated with stress, indoor-only living, and low water turnover, and flares are often triggered by changes in the household. The inflamed bladder lining creates a persistent urge to urinate even when only small volumes are produced, so a cat with cystitis alone typically leaves several small clumps or spots of urine, sometimes blood-tinged. In male cats, the mucus plugs and spasm associated with idiopathic cystitis are the most commonly reported cause of urethral obstruction, and the straining posture looks much the same in both. A partly blocked male cat can also still pass a few drops, so spots of urine alone do not separate cystitis from a blockage.
Bladder or Urethral Stones (Urolithiasis)
Struvite or calcium oxalate crystals can aggregate into stones that sit in the bladder or migrate towards the urethra. Their presence irritates the bladder lining and can partially obstruct urine flow, both of which prompt frequent, often unproductive, visits to the tray. Diet, hydration, and urine pH all influence which stone type forms. Stones account for roughly one in ten to one in five cats with lower urinary tract signs, and in male cats a small stone can move into the urethra and block it.
Litter Tray Environment and Behaviour
A tray that is soiled, poorly positioned, filled with an unfamiliar substrate, or contested by other cats can lead to repeated entering, sniffing, and scratching without urinating, independent of any bladder disease. A cat avoiding an unpleasant tray tends to make brief visits, perch on the edge, skip covering, or urinate elsewhere, and still passes normal-sized clumps of urine somewhere. This pattern is common in multi-cat households, follows changes in tray management, and tends to settle when the number, cleanliness or position of trays changes. Straining with little or no urine produced is not explained by tray preferences, and behavioural causes are generally only assigned once bladder disease has been excluded.
Constipation
Straining to pass faeces looks very similar to straining to urinate. Constipation is more common in older cats and in those with kidney disease, dehydration or arthritis that makes squatting painful. A constipated cat typically still leaves normal urine clumps, whereas a blocked cat leaves none or only a few drops. The resemblance runs both ways: a urinary blockage in a male cat is frequently mistaken for constipation, which is one of the ways a blockage is missed.
Bacterial Urinary Tract Infection
True bacterial infection is uncommon in otherwise healthy cats under ten years old, accounting for under 1% to about 8% of those with lower urinary tract signs across studies. It is more likely in older and female cats and in cats with chronic kidney disease, diabetes mellitus or hyperthyroidism, where frequent small voids may be the first sign. Urine culture is what separates infection from sterile cystitis.
Why timing matters
Early observation
Frequent small urinations with some urine still being passed usually reflect bladder inflammation, most often idiopathic cystitis. In a male cat, however, a few drops of urine do not rule out a blockage, because a partly blocked urethra can still let some urine through. The same posture with nothing produced, especially in a male cat, fits a blocked urethra. From outside the tray these can look identical, and around one in eight obstructed cats has already developed severe electrolyte and acid-base changes by the time it is examined.
Later presentation
In a blocked cat the picture changes over hours. Kidney values can rise within 24 to 48 hours of complete obstruction, followed by vomiting, dullness and a slowing heart rhythm from high potassium, and death can follow within about three days without relief. A quiet cat that has stopped visiting the tray may be further along this course rather than improving.
The sex of the cat and whether any urine is being produced matter more than how long the behaviour has lasted. Female cats very rarely obstruct, and cats of either sex passing small amounts of urine more often have cystitis, although in a male cat a few drops are also consistent with a partial blockage. A male cat producing only drops or nothing fits the pattern in which hours can change the outcome, and whether the bladder is full and hard can only be established by examination.
Conditions commonly associated
Urethral Obstruction
Blocked cats, almost always male, visit the litter tray repeatedly but pass little or no urine. This is the cause of the sign in which delay changes the outcome: potassium and waste products can reach dangerous levels within hours to a day or two of the blockage starting, which is rarely witnessed, and the behaviour is often mistaken for constipation.
Feline Idiopathic Cystitis
Feline idiopathic cystitis often causes bladder wall inflammation and discomfort that prompts frequent attempts to urinate, yet the associated pain or bladder spasm can make it difficult to pass urine, resulting in repeated unproductive visits. The stress-related nature of the condition can amplify this pattern during periods of environmental change. In male cats, the mucus plugs and spasm associated with idiopathic cystitis are the most commonly reported cause of complete obstruction.
Transitional Cell Carcinoma
Transitional cell carcinoma is an uncommon bladder tumour in cats, seen mainly in older cats, and can cause straining, frequent small voids and blood in the urine that resemble cystitis. Unlike in dogs, where these tumours usually sit at the bladder neck, in cats they are more often found in the body or apex of the bladder, so a urethral blockage is a less typical feature. New lower urinary tract signs in an older cat make causes other than idiopathic cystitis more likely.
Diabetes Mellitus in Cats
Diabetic cats have a higher risk of bacterial urinary tract infection, which can cause frequent small voids with straining. Diabetes itself more often causes the opposite pattern, frequent visits that produce large clumps of dilute urine because of increased thirst and urine output, which can be mistaken for the unproductive form.
Chronic Kidney Disease in Cats
Cats with chronic kidney disease produce more dilute urine and more often have bacteria in the urine, sometimes with a true infection that causes frequent, small, uncomfortable voids. As with diabetes, the larger urine volume of kidney disease more often causes frequent productive visits than unproductive ones, and dehydration linked to kidney disease also makes constipation more likely.
Urinary Stones (Urolithiasis)
Bladder and urethral stones irritate the bladder lining and can partly or completely block urine flow, causing repeated straining with small or absent volumes. In male cats a stone moving into the urethra is a recognised cause of complete obstruction.
Constipation and Megacolon in Cats
Straining to pass faeces looks similar to straining to urinate, and a urinary blockage is often mistaken for constipation. Whether normal-sized urine clumps are appearing in the tray is one clue visible at home, but an imperfect one, because a partly blocked male cat can still pass a few drops; examination distinguishes a full bladder from a full colon.
Inappropriate Elimination in Cats
Litter tray aversion and bladder inflammation can both produce tray visits without normal urination, and cats with cystitis often urinate outside the tray. Behavioural explanations are generally assigned only after bladder disease has been excluded.
When to explore further
When a cat, particularly a male cat, is straining in the tray and no urine clumps or wet patches, or only a few drops, are appearing, since a complete urethral blockage can become life-threatening within hours to a day or two of it starting, which is rarely witnessed
When straining is accompanied by vomiting, hiding, crying out, repeated licking of the genital area, weakness or collapse, which can reflect potassium and waste products building up in the blood
When it is unclear whether the cat is straining to pass urine or faeces, because the two look alike and the urinary form is the one in which hours matter
When small, frequent, sometimes blood-tinged urinations recur, as repeated cystitis or stones in a male cat carry an ongoing risk of blockage
Useful details include the cat's sex, whether urine clumps or wet patches are appearing and roughly how large they are, when urine was last seen passed normally, whether blood is present, and whether vomiting, hiding or crying out have appeared. Recent household changes, diet and water intake are relevant to cystitis and stones. The fullness of the bladder, which separates cystitis from a blockage, cannot be assessed reliably at home, so these details are most informative alongside an examination.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS