Stone Age? Not quite! But whether struvite, calcium oxalate, urate or cystine stones, all of these urinary stones are a common problem in animal patients with urinary tract diseases. Did you know that cats and dogs can be equally affected? We give you an insight into the formation, symptoms and treatment options for struvite stones.
What are struvite stones anyway?
Urinary stones are concretions that can occur in the urinary tract of our animals due to the precipitation of mineral components as part of urolithiasis. Struvite stones are a type of urinary stone and consist mainly of magnesium ammonium phosphate. In urine, struvite stones appear colorless and sharp-edged, mostly in the shape of a coffin lid. Crazy, right? But they all have one thing in common: They put our furry friends in a really tricky situation.
How do struvite stones form?
Various factors can contribute to the formation of urinary stones. Struvite stones can occur in connection with urinary tract infections. The bacteria that possess the enzyme urease break down the urea contained in the urine into ammonia and carbon dioxide. The pH value of the urine increases due to the increased concentration of bicarbonate and ammonium. The alkalinization of the urine can cause precipitation of minerals such as magnesium, ammonium and phosphate. Consequently, a change in the pH value of the urine plays a decisive role in the formation of struvite stones. But factors such as an increased concentration of magnesium, ammonium and phosphate in the urine and insufficient water intake can also play a role. Overall, urinary stone formation can occur quickly and there is also the possibility that bacteria can become trapped and persist within the stones.
pH value
The pH value of urine indicates how acidic or basic the urine is. More precisely, the pH value describes the hydrogen ion concentration in a liquid. The pH value is crucial for inhibiting or activating crystallization. An alkaline pH value, greater than 7 to 7.5, influences the precipitation of struvite and calcium apatite crystals. An alkaline pH value therefore promotes the formation of these stones. Acidic urine with a pH value of 5.5 to 6 can promote the precipitation of calcium oxalate, cystine and urate crystals.
The pH value can be measured using a pH stick or calculated using the cation-anion ratio. In healthy cats and dogs, the pH value should be around 6.5. The measurement times depend on the feeding of the patients. After feeding, the urine becomes alkaline and with prolonged obstruction, the pH value is more acidic.
Risk factors – who is affected?
- Predisposed breeds
- Obesity
- Feeding – dry food only
- Old age
- Gender
- Urinary tract infections
- Metabolic disorders
- Insufficient drinking habits
There are certain factors that can increase the risk of struvite stone formation in small animals. In cats, there are predisposing breeds, such as Persian cats, which are more susceptible to struvite stones due to their altered urine composition. In dogs, miniature schnauzers, dachshunds and retrievers are often affected. Obesity, lack of exercise and exclusively dry food feeding with insufficient water intake also play a role in the formation of urinary stones. In addition, certain underlying diseases such as urinary tract infections or metabolic disorders can increase the risk of struvite stone formation.
Symptoms
- Polyuria
- Dysuria
- Hematuria
- Incontinence
- Behavioral change
Get the ball rolling
The treatment of struvite stones aims to dissolve the stones and prevent new ones from forming. The first method for dissolving struvite stones is dietary measures. This involves the use of special diet feed or additives that lower the pH of the urine and reduce the magnesium, ammonium and phosphate content. A pH of 6.0 to 6.5 is aimed for therapy, which can promote the dissolution of the stones. It is also important to provide the animal with sufficient fresh water to dilute the urine concentration and flush the urinary tract. Dietary measures are not sufficient to treat urinary stones in all cases. In these cases, surgical interventions are necessary to remove the stones. The type of treatment depends on the composition, size, location and symptoms caused by the urinary stones.
Prophylaxis
A lot can also be done to prevent struvite stones: A balanced diet that is tailored to the individual needs of the animal can help to optimize the urine composition and thus prevent the formation of struvite stones. Dietetics in dogs and cats can be used prophylactically and therapeutically. The aim of the dietary measures is to lower the pH value and reduce the intake of stone-forming substances such as magnesium, calcium and phosphate. During the prophylaxis of struvite stones, a pH value of 6.6 to 6.8 should be aimed for. High-quality wet food options are important, which have a higher water content than dry food and can contribute to sufficient fluid intake. The provision of fresh, clean water is also of great importance. In addition, the solubility of the renally excreted substances should be improved by a high urine flow, an optimal pH value and a solubilizer or inhibitor of concretion formation. In addition, unnecessarily high levels of alkalizing ingredients in feed can be avoided.
The targeted acidification of urine, for example through the amino acid methionine, can prevent the formation of struvite stones and even partially dissolve the stones. If sufficient intake of the sulfur-containing amino acid is used, sulfate is formed, which is excreted renally. The formation and secretion of protons in the urine lowers the pH value. Methionine also reduces the adhesion of bacteria to the urothelial cells.
The next time you see a patient with struvite stones in your practice, the treatment may vary depending on the size of the urinary stone. Small stones can be dissolved by acidifying the urine. If this is not possible, surgical intervention is necessary, followed by prophylaxis against the formation of new struvite stones. Lowering the pH value, whether for the treatment or metaphylaxis of struvite stones, is very important.
June 30, 2024 – by Linn Masch
