Renal failure in dogs after ingestion of raisins or grapes
Both grapes and raisins are very dangerous foods for dogs and are a frequent cause of poisoning. This was highlighted in a study1 conducted between August 1994 and September 2007 by researchers at the Veterinary Poisons Information Service, London, which analysed the clinical course of 169 cases of poisoning from Vitis vinifera grapes and raisins.
The results showed that animals who ingested larger quantities of grapes or raisins, consequently had more severe signs of toxicity, regardless of their age, sex or breed. As one might expect, raisins were more harmful than grapes, as they have a higher concentration of the toxins that are naturally present in grapes.
The ingestion of grapes and raisins also increases the concentration of blood urea nitrogen and/or creatinine, which can trigger kidney failure in dogs, a disease characterised by impaired kidney function that affects the correct elimination of body fluids.
Signs of kidney failure in dogs due to the ingestion of grapes or raisins
The signs of poisoning by grapes or raisins first manifest about 6 hours after ingestion. The clinical presentation typically includes:
- Vomiting
- Diarrhoea
- Abdominal tenderness
- Lethargy
- Loss of appetite or anorexia
- Dehydration
- Remains of grapes or raisins in stools or vomit
- Polydipsia
- Oliguria
- Anuria
Laboratory tests usually reveal elevated blood urea or creatinine, as reported in a review2 by the American Society for the Prevention of Cruelty to Animals of a canine toxicology database that included 43 dogs poisoned with grapes, raisins or both.
Furthermore, 95% of the dogs poisoned by grapes or raisins presented an increased calcium–phosphorus product, while 90% had hyperphosphataemia, a fluid–electrolyte disorder due to abnormally high blood phosphate levels, and 62% suffered from hypercalcaemia, another fluid–electrolyte disorder involving elevated plasma calcium levels.
It should be noted that we have not yet deduced the toxic principle and the exact mechanism of grape-induced nephrotoxicity, but it is believed that its harmful effects are related to a nephrotoxic agent or idiosyncratic reaction, which in turn leads to hypovolaemic shock or renal ischaemia.
Consequences and prognosis of kidney failure in dogs due to the ingestion of grapes or raisins
The most obvious consequence of kidney failure in dogs following the ingestion of grapes or raisins is impaired kidney function, which means patients are unable to expel toxins from the body in the urine. In some cases, dogs may void a small volume of dark urine or stop urinating altogether, or, contrastingly, they may void large volumes of a very clear urine. Both are indications of impaired kidney function.
In the aforementioned review by experts at the American Society for the Prevention of Cruelty to Animals2, proximal renal tubular necrosis, which affects renal tubule cells, was the most frequent histological consequence in dogs poisoned by grapes or raisins. Kidney failure in dogs also affects blood pressure even inducing a coma in more severe cases or, in the worst-case scenario, death.
In fact, of the 43 dogs assessed, only 23 survived and 15 enjoyed complete remission of the clinical signs. Five dogs died naturally due directly to poisoning by the grapes or raisins and 15 had to be euthanised.
Dogs with oliguria or anuria usually have an unfavourable prognosis. A high calcium concentration and calcium–phosphorus product are indicative of a negative prognosis. In fact, kidney failure in dogs due to the ingestion of grapes or raisins has a fairly high mortality rate and it is estimated that around 50% of dogs die from kidney failure after eating them.
However, if the patient has a high degree of tolerance to grapes and raisins and receives early treatment, the prognosis may be favourable. A study carried out at the University of Milan3 revealed that there is significant variability in the degree of tolerance to grapes and raisins; while some dogs remain asymptomatic after consuming a kilo of raisins, others die from the ingestion of a few grapes. Affected dogs can lead a normal life if and when they recover, although changes need to be introduced to the lifestyle of any patients who have suffered kidney damage, above all their diet.
Treatment of kidney failure in dogs after the ingestion of grapes or raisins
Time is a crucial factor in the treatment of kidney failure in dogs following the ingestion of grapes or raisins. The diagnosis should be confirmed through clinical examinations and laboratory tests.
The treatment of choice is usually the use of emetic agents, such as activated charcoal to induce vomiting, so that patients can expel as much of the toxin as possible. Intravenous fluids should be administered for at least 48–72 hours to regulate the dog’s renal function and fluid balance. Kidney function should also be monitored for at least 72 hours.
When the patient returns home, it is important to opt for a renal diet that helps regulate kidney function, especially if the dog has suffered kidney damage. The Advance Veterinary Diets Renal is an excellent solution as it is high in soluble fibre and low in phosphorus, sodium and proteins, which helps reduce renal load and control acidosis.
