Lizard gout and kidney disease: the diet and water behind them

Quick answer

Reptiles do not excrete their nitrogen waste as urea in urine the way mammals do. They convert it to uric acid and pass it as a semi-solid white paste, which saves an enormous amount of water and is why a lizard can live somewhere a mammal cannot.

The cost of that adaptation is that uric acid barely dissolves. If the blood level rises, because the animal is dehydrated, because the diet contains more protein than the species is built for, or because the kidneys are failing, it comes out of solution and forms crystals in joints and organs. That is gout, and by the time it is visible it is usually permanent.

What goes in the bowl and how the animal drinks are the two things that decide whether this happens.

• Uric acid is barely soluble. Dehydration and excess protein are the two things that push it out of solution.
• Herbivorous lizards fed dog food, cat food or high-protein pellets are the classic gout case.
• Desert species need water. They get it in the wild from humid burrows, dew and food, not from being dry all the time.
• Watch the white part of the droppings. Urates are the most useful thing an owner can monitor.
• Over-supplementing vitamin D3 damages kidneys. More is not safer.

:::danger
Never feed dog food, cat food, monkey biscuit or high-protein pellets to a herbivorous lizard.

Green iguanas, uromastyx and other plant-eating species have kidneys built for a low-protein plant diet. Loading them with animal protein raises blood uric acid steadily, and the damage accumulates silently for months or years before the first swollen joint appears. It is one of the best documented causes of gout in captive reptiles and it is entirely avoidable.
:::

Decide in 60 seconds

Why uric acid is the whole story

A mammal makes urea, which dissolves easily, and flushes it out in a large volume of water. That works if water is plentiful.

Reptiles took the other route. They convert nitrogen waste to uric acid, which needs almost no water to excrete because it leaves as a paste rather than a solution. It is an elegant adaptation for a dry environment and it is why a desert lizard can go a long time without drinking.

The trade-off is chemical. Uric acid is poorly soluble, so blood can only hold so much before it starts crystallising out. Three things push it over that line.

Dehydration concentrates the blood, so the same amount of uric acid is now above the threshold.

Excess protein increases how much uric acid is produced in the first place, and the effect is largest in species whose kidneys evolved for a plant diet.

Reduced kidney function slows clearance, so uric acid accumulates even at normal production.

Once the crystals form, they lodge where blood flow is slow and temperature is lower: the small joints of the toes, the elbows, the knees, and around tendon sheaths. They also deposit on the surface of internal organs, in the pericardium around the heart, in the kidneys themselves and in the liver.

Crystals in a joint destroy the cartilage. That damage does not reverse when the blood chemistry is corrected, which is why this is a prevention topic rather than a treatment topic.

The causes, in order of how often they matter

Chronic dehydration.

The single biggest contributor, and the one most often missed because the animal looks fine.

The mistake is usually conceptual. Owners of desert species are told the animal does not need humidity, so they provide a dry enclosure with a small bowl and high basking temperatures. In the wild, that same species spends much of its time in a burrow where the humidity is far higher than at the surface, drinks from dew and rain, and takes water from its food.

Other common versions: a chameleon given a standing water bowl, which it will never use because it drinks moving droplets from leaves; a water bowl too small or too high to reach; a bowl that is never cleaned so the animal avoids it; a species that drinks by lapping mist and is never misted; and a basking temperature set too high, which increases evaporative loss all day.

Dietary protein in the wrong species.

Green iguanas fed dog or cat food, uromastyx fed insects or high-protein pellets, and herbivorous lizards given beans, peas and other legumes as a staple. This is a documented and repeatable route to gout.

The reverse error exists too: insectivorous species fed almost exclusively on high-fat, poorly gut-loaded insects develop their own problems, including obesity and liver disease, and an obese lizard tolerates renal insult badly.

Vitamin D3 over-supplementation.

The instinct after reading about metabolic bone disease is to add more calcium and more D3. Excess D3 causes calcium to be deposited in soft tissue, including the kidneys and blood vessels, and that is a mechanism for kidney failure rather than for bone strength. Supplementation needs to be matched to the species, the diet, the age of the animal and the ultraviolet provision, and that is a conversation with a reptile vet rather than a decision made from a label.

Nephrotoxic drugs.

Some antibiotics and anti-inflammatories are harmful to reptile kidneys, particularly in a dehydrated animal. This is one of several reasons not to use leftover medication from another animal, and why vets often give fluids before or alongside treatment.

Infection, tumours and age.

Renal disease in reptiles also arises from infection, from neoplasia and simply from getting old. An older lizard with any of the signs below deserves bloodwork rather than a husbandry tweak.

Weighing what is offered and knowing what the species should eat is the intervention with the biggest effect. Most gout cases begin in a food bowl.

Reading the urates

The white portion of a lizard's droppings is the part that tells you about hydration and kidney function, and it is checked far less often than the faecal part.

Normal.

White to off-white, or a very pale cream. Soft, with the consistency of toothpaste or soft chalk. Passed with or just after the faeces. Some species pass urates separately.

Yellow or orange.

A common finding in dehydrated reptiles, and worth investigating rather than assuming it is dietary pigment.

Hard, gritty or chalky.

Suggests the urates have been concentrated, either from dehydration or reduced renal water handling.

Very small or absent.

Concerning. A reptile that passes faeces with no urates, or nothing at all, needs assessing.

Green tinged.

Bile pigment reaching the urate portion. Worth reporting.

Photograph the droppings on a light background before you clean them out. Colour and consistency change quickly, and a photograph is much more useful than a recollection.

The signs of renal disease, in order of appearance

Early, and easy to dismiss.

Reduced appetite, gradual weight loss, less time basking or climbing, a slightly dull appearance to the skin.

Dehydration signs.

Eyes that look sunken into the sockets, skin that stays wrinkled or tented after being gently lifted, tacky mucous membranes, and dry, dull skin that sheds poorly.

Constipation and straining.

An important species-specific sign. In many lizards the kidneys sit inside the pelvic canal, so as they enlarge they narrow the passage that faeces must travel through. A lizard straining, producing small droppings or none, with a swollen appearance behind the hips, may have a kidney problem rather than a gut one.

Hind limb weakness.

Gradual weakness or dragging, from pressure on nerves in the same pelvic region.

Muscle loss over the hips and tail base.

Often noticed as the animal looking bony at the back end while the middle stays full.

Joint swelling.

Firm, warm, painful swellings around the toes, elbows or knees, sometimes with visible white deposits under the skin. The lizard is reluctant to move, will not climb, and may hold a limb off the ground.

Mouth changes.

Pale or dry membranes, and in advanced disease ulceration or necrosis of the oral tissue.

Sudden collapse.

Visceral gout can be silent until the deposits around the heart or in the kidneys cause failure, and some cases are only diagnosed after death.

Getting hydration right by species

Desert species such as bearded dragons and uromastyx.

A clean water bowl they can reach, a humid hide or a burrow area with damp substrate underneath a dry surface, and an appropriate ambient humidity rather than a bone-dry enclosure. Do not push basking temperatures above the species range, because a hotter animal loses more water all day.

Chameleons.

Will not drink from standing water. They need moving droplets: a dripper, regular misting, or both, timed so the enclosure dries out between sessions to avoid respiratory problems.

Geckos.

Many are crepuscular and lap condensation. Provide a humid hide, mist appropriately for the species, and offer a shallow bowl.

Tropical and forest species.

Higher ambient humidity with genuine airflow, and misting or a dripper.

All species.

Clean the bowl daily. Reptiles avoid fouled water. Position it where the animal actually goes rather than where it is convenient. Check that the animal can get into and out of it easily.

Soaking.

Shallow warm soaks help some species and some situations, particularly a mildly dehydrated animal or one with a shedding problem. They are not a substitute for constant water access and correct humidity, they are not appropriate for a reptile in respiratory difficulty, and the water must be shallow enough that the animal cannot be submerged.

For a herbivore, the whole diet should look like this: leaves and vegetables with a suitable calcium to phosphorus balance, and no animal protein at all.

What never to do

Do not feed dog food, cat food, monkey biscuit or any high-protein pellet to a herbivorous lizard.

Do not use beans, peas or lentils as a staple for a herbivore.

Do not keep a desert species in a completely dry enclosure on the reasoning that it comes from a desert.

Do not add vitamin D3 or calcium at every feed without a plan agreed for your species and setup.

Do not give leftover antibiotics or anti-inflammatories from another animal, and never give any medication to a dehydrated reptile without veterinary direction.

Do not treat swollen joints as an injury and wait. Gout, septic arthritis and metabolic bone disease all cause joint swelling and they need imaging to separate.

Do not raise basking temperatures to encourage appetite in an animal that is already losing weight.

Do not assume a lizard drinks simply because there is a bowl in the enclosure. Watch it drink, or provide the method its species actually uses.

When to get help

Go the same day for any lizard passing no urates, straining without producing droppings, unable to use its hind limbs, or with joints that are hot, swollen and clearly painful.

Book an appointment promptly for firm joint swellings, white deposits under the skin, gradual weight loss with muscle wastage over the hips, urates that are yellow, orange, gritty or hard, or a herbivorous lizard that has been fed animal protein.

Ask for baseline bloods and a husbandry review for any lizard over middle age, especially if it has ever been fed inappropriately or kept in a dry enclosure. Renal disease is far more manageable when it is found on a blood test than when it is found by a swollen toe.

Bring the exact diet with brand names, the supplement schedule, the ultraviolet lamp details and installation date, measured temperatures and humidity, weight now and previously, photographs of the urates, and a note of when the animal last drank, ate and passed droppings.

A well-hydrated lizard on the right diet: soft white urates, steady weight, and easy movement into and out of the basking site.