Blood in your guinea pig’s urine usually signals a problem in the urinary tract, most commonly a bladder stone, a bacterial infection, or both. About 43% of guinea pigs that show up at a vet with urinary or genital symptoms turn out to have bladder stones, making it the single most likely explanation. This is not something that resolves on its own, and your guinea pig needs veterinary attention soon.
It Might Not Actually Be Blood
Before you panic, it’s worth knowing that guinea pig urine can naturally range from pale yellow to deep orange, and certain plant pigments called porphyrins can turn it red without any blood being present. Beets, red cabbage, and some leafy greens are common culprits. A urine dipstick test will react to blood, but it also reacts to other substances, so the only reliable way to confirm actual blood cells is microscopic examination of the urine sediment by a vet. One useful trick: porphyrin pigments from food glow under ultraviolet light (a Wood’s lamp), while blood does not.
If the red color appeared suddenly, comes and goes, or is accompanied by any behavioral changes, treat it as blood until proven otherwise.
Bladder Stones: The Most Common Cause
Guinea pigs are uniquely prone to forming urinary stones because of how their bodies handle calcium. Like rabbits and other herbivores, they absorb most of the calcium from their food and then dump up to 75% of the excess through their kidneys. That calcium-heavy urine, combined with their naturally alkaline urine pH, creates ideal conditions for crystals to form and grow into stones.
The stones are primarily made of calcium carbonate, though calcium oxalate stones also occur. They most often develop in the bladder or urethra, where they scrape and irritate the lining, causing visible blood in the urine. You may also notice your guinea pig straining to urinate, producing only small amounts at a time, crying out or squeaking loudly while peeing, or arching their back in pain. Some guinea pigs stop eating because of the discomfort.
Diet plays a major role. Alfalfa-based hay and pellets are significantly higher in calcium than timothy hay, and feeding too many calcium-rich vegetables (like kale, spinach, or parsley) adds to the problem. The recommended calcium-to-phosphorus ratio in a guinea pig’s diet is roughly 2:1, which means about 8 grams of calcium per kilogram of food to 4 grams of phosphorus. Adult guinea pigs should be eating timothy hay rather than alfalfa, with pellets formulated for adults.
Low water intake makes everything worse. When guinea pigs don’t drink enough, their urine becomes more concentrated, giving calcium salts more opportunity to crystallize. Offering fresh water in both a bottle and a bowl, keeping the water clean, and adding water-rich vegetables like cucumber or bell pepper can help encourage drinking.
Urinary Tract Infections
Bacterial infections of the bladder are also common in guinea pigs and frequently occur alongside stones. The stone irritates the bladder wall, creating a welcoming environment for bacteria, and the infection in turn promotes further stone growth. It becomes a cycle that’s hard to break without treating both problems.
The bacteria most often involved are Pseudomonas, Staphylococcus, and E. coli, and infections frequently involve more than one bacterial species at the same time. Signs of a UTI overlap heavily with stone symptoms: blood in the urine, straining, frequent small urinations, lethargy, loss of appetite, and sometimes a discharge from the urethral opening.
A vet will typically collect a urine sample for both analysis and bacterial culture. The culture identifies exactly which bacteria are present and which treatments will work against them, since guinea pigs are sensitive to certain types of antibiotics that are safe for other animals. Treatment generally involves a course of antibiotics chosen based on those culture results.
Less Common Causes
Bladder inflammation without infection (similar to interstitial cystitis in humans) can also produce bloody urine. In this condition, the bladder wall becomes inflamed and hypersensitive through a self-reinforcing cycle of irritation. Inflammatory chemicals irritate nerve endings in the bladder, which release more inflammatory chemicals, which cause more irritation. The result is chronic discomfort and bloody urine even after any original trigger has resolved.
Reproductive problems can also cause what looks like blood in the urine, particularly in unspayed females. Uterine tumors, ovarian cysts, and uterine infections can all produce bloody discharge that mixes with urine and is easy to mistake for urinary bleeding. If your female guinea pig hasn’t been spayed, your vet will likely check for reproductive issues as part of the workup.
What Happens at the Vet
A proper diagnostic workup includes a physical exam, abdominal X-rays, ultrasound, urinalysis, and a bacterial culture of the urine. The X-ray is particularly important because calcium carbonate stones are dense and show up clearly on radiographs. Ultrasound adds detail about the bladder wall, kidney health, and any stones that might be harder to see on X-ray.
If stones are found, the treatment depends on their size and location. Small stones sometimes pass on their own with increased hydration, but most bladder stones in guinea pigs require surgical removal. Guinea pigs tolerate the surgery well in most cases, though recovery involves pain management and monitoring for a week or two afterward. If the stone is lodged in the urethra and blocking urine flow entirely, that’s an emergency requiring immediate care.
For infections without stones, antibiotics based on culture results are the standard treatment. Your vet will likely want a follow-up urine test after the course is finished to confirm the infection has cleared.
Reducing the Risk Going Forward
Prevention centers on three things: diet, hydration, and regular monitoring. Switch to timothy hay as the primary food source if you haven’t already, and choose timothy-based pellets rather than alfalfa-based ones. Limit high-calcium greens and rotate vegetables so your guinea pig isn’t getting a calcium-heavy mix every day. Bell peppers, romaine lettuce, and cucumber are lower-calcium options that still provide vitamin C, which guinea pigs need daily since they can’t produce it themselves.
Encourage water intake by keeping water sources clean and accessible. Some guinea pigs drink more from a bowl than a bottle, so offering both can help. Adding a slice of cucumber or a small amount of unsweetened fruit juice to the water occasionally may tempt a reluctant drinker, though you should change the water frequently if you do this.
Pay attention to how your guinea pig urinates. Changes in frequency, volume, color, or any signs of straining or vocalization during urination are early warning signs. Guinea pigs are prey animals that instinctively hide illness, so by the time symptoms are obvious, the problem has often been developing for a while. Regular vet checkups that include a urine sample can catch issues before they become serious.