SYMPTOM
Dark or discoloured urine
Owners may observe that their pet's urine has become darker than usual, appearing brown, red, reddish-brown, port-wine coloured, or orange rather than the typical yellow colour.
Haemolysis (red blood cell destruction)
When red blood cells are destroyed in large numbers, whether through immune-mediated processes, toxin exposure, or infection, pigment reaches the urine by two routes. Red cells that burst within the bloodstream (intravascular haemolysis) release free haemoglobin, which spills into the urine and turns it red, reddish-brown, or port-wine coloured (haemoglobinuria). Red cells removed from the circulation by the body's own scavenger cells (extravascular haemolysis) are broken down to bilirubin, which gives dark yellow to orange-brown urine (bilirubinuria). Jaundice can accompany either route. Published mortality rates for immune-mediated haemolytic anaemia range from 20% to 75%, and in dogs the period of highest risk is the first 2 weeks after treatment starts, so urine of these colours alongside pale or yellow gums carries considerable clinical weight.
Liver or biliary disease
Conditions affecting the liver's ability to process and excrete bilirubin can lead to spillover of bilirubin into the urine, producing a dark yellow, orange, or brownish discolouration. Hepatic disease, biliary obstruction, and other conditions that impair bilirubin metabolism may all contribute to changes in urine colour through this mechanism.
Muscle damage (rhabdomyolysis)
Severe muscle damage releases myoglobin (the oxygen-storing protein found in muscle tissue) into the bloodstream. This myoglobin is filtered by the kidneys and excreted in the urine, producing a dark brown or cola-coloured appearance. Causes may include extreme exertion, crush injuries, certain toxins, or prolonged seizure activity.
Urinary tract conditions
While blood in the urine (haematuria) typically produces a red or pink discolouration, small amounts of bleeding or old blood within the urinary tract can sometimes produce darker, brownish urine. Infections, stones, or other conditions affecting the kidneys, ureters, bladder, or urethra may alter urine colour in various ways.
Medicines and dyes
Pigments from outside the body, including some medicines and dyes, can alter urine colour without indicating a pathological process. Colour from such a pigment cannot be told apart by eye from colour produced by disease.
Why timing matters
Early observation
When a change in urine colour is first noticed, the timing and context can provide useful information. A single episode of darker yellow urine may relate to concentration (dehydration) or to a medicine. However, a clear shift from normal yellow to brown, reddish-brown, or orange suggests that pigments not normally present in significant quantities are being excreted by the kidneys, and that holds for a single urination as much as for a repeated one.
Later presentation
Persistent dark or discoloured urine, especially when accompanied by other changes such as pale gums, jaundice, lethargy, or reduced appetite, may indicate an ongoing process of red blood cell destruction, liver dysfunction, or other condition affecting how the body handles waste pigments. The combination of urine colour change with pale gums or jaundice points towards red blood cell destruction or liver and biliary disease, and the degree of anaemia cannot be judged at home.
The speed at which a urine colour change develops can be informative. Discolouration that appears suddenly and intensifies over days may suggest an acute process such as rapid haemolysis, whilst more gradual changes may indicate a slower-developing condition. Fluctuations in how deep the yellow colour is (darker at some times and more normal at others) may relate to variations in hydration status. Brown, reddish-brown, or port-wine coloured urine that comes and goes may reflect an intermittent underlying process, and a return to normal colour does not show that the process has stopped.
Conditions commonly associated
Immune-Mediated Haemolytic Anaemia (IMHA)
Dark or discoloured urine in IMHA results from pigment released as red blood cells are destroyed: bilirubin, and free haemoglobin when the cells burst within the bloodstream (intravascular haemolysis).
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Liver Disease in Dogs
Liver disease can cause bilirubin accumulation in the bloodstream, resulting in orange to brown discolouration of urine as excess bilirubin is excreted by the kidneys.
Allium Toxicity (Onion and Garlic)
Damaged red blood cells release pigment into the bloodstream, which can darken the urine after allium ingestion.
Babesiosis
Haemoglobin released from destroyed red blood cells is filtered into the urine, darkening its colour.
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Bile Duct Obstruction
Bilirubin that cannot pass into the gut is instead excreted through the kidneys, darkening the urine.
When to explore further
When urine has become a consistently deeper yellow than the animal's normal colour, particularly if the change has persisted across multiple urinations and is not explained by dehydration or a medicine.
When dark urine appears alongside other signs such as pale gums, jaundice, lethargy, or reduced appetite, suggesting a systemic process rather than an isolated urinary change.
When the urine appears distinctly brown, reddish-brown, or port-wine coloured rather than simply concentrated yellow, as these specific discolourations may indicate the presence of blood, haemoglobin, bilirubin, or myoglobin. Blood, haemoglobin and myoglobin cannot be told apart by eye: all three give the same reaction on a urine test strip, and the distinction rests on examination of the urine sediment and a blood sample.
When dark urine develops after starting a new medicine, following intense physical activity, or in association with a known illness, as the temporal relationship may help identify the underlying cause.
For urine that is a deeper yellow than usual, noting the colour, clarity, and any odour changes over time can help establish whether the change is an isolated occurrence or a developing pattern. Brown, reddish-brown, or port-wine coloured urine reflects pigment rather than concentration, and its significance does not depend on a pattern developing. Observing urine against a light surface or collecting a small sample in a clear container can make colour assessment more reliable than trying to evaluate it on grass or dark surfaces. Other changes in the animal's wellbeing noticed at the same time, such as pale or yellow gums, lethargy, or reduced appetite, add context to any colour change.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS