Second condition we need to check for is congenital kidney dysfunction
This condition can happen in us too. Some People are born with 1 kidney or 2 small kidneys etc. Blood work and Ultrasound imaging would check for this
Third condition is liver shunt
A portosystemic shunt (PSS, portasystemic shunt, portocaval shunt, portacaval shunt, liver shunt, hepatic shunt, or porto-systemic vascular anomaly) happens when a pet’s venous blood from the stomach, intestines, pancreas, and spleen bypasses the liver. The pet can be born with the shunt (congenital) or can get it later (acquired). About 80% of the cases are congenital, although sometimes a pet can have both types. About 25-33% of the congenital shunts are within the liver. Approximately 0.18% of all dogs have congenital shunting.
During pregnancy, the portal blood vessel in the fetus bypasses the liver (the mother’s liver filters out toxins for the fetus). Normally this shunt closes within three days after birth. In affected animals, the shunt doesn't close and the blood continues to bypass the liver. Because the liver filters toxins, if it is bypassed the toxins build up in the body. This results in the puppy or kitten having slow or nonexistent growth (failure to thrive). If left untreated, puppies and kittens are not likely to survive.
Congenital shunts seem to happen more in purebreds than in mixed breeds. Breeds with increased risk of PSS include Yorkshire terrier, Maltese terrier, Silky terrier, miniature schnauzer, miniature and toy poodles, Lhasa apso, Bichon Frise, shih tzu, Havanese, Dandie Dinmont terrier, Pekingese, German shepherd dog, golden retriever, Doberman pinscher, Labrador retriever, Irish setter, Samoyed, Old English sheepdog, Irish wolfhound, Australian shepherd, Australian cattle dog, Himalayan, and Persian.
No sex predisposition has been documented.
An acquired liver shunt is usually caused by liver problems (hepatic cirrhosis, portal hypertension, hepatic arterio-venous malformations, etc.) that resulted in the body routing blood through whatever blood vessels are available, even if it means bypassing the liver. (It would be like taking side streets to your final destination, instead of using the interstate highway.) As happens with congenital shunts, the liver can't filter what doesn't pass through it, so toxins build up in the body.
Signs include stunted growth, not gaining weight, losing weight, vomiting, diarrhea, lethargy, unresponsiveness, temporary blindness, seizures, spaciness (staring into space), disorientation, circling, poor skin and coat, excessive drinking, excessive urination, etc. Sometimes the pet will just act odd after eating, or pace around or press his head against the wall. The signs you will see depend on the location of the shunt and how many toxins have built up in the body. Some pets will only have one sign, while others could have several. Many of the clinical signs associated with PSSs are related to hepatic encephalopathy.
Clinical signs, blood tests, urinalysis, and imaging tests (e.g., radiographs, ultrasound images, portograms [an image of the blood vessels to the liver], or nuclear scintigraphy [a nuclear scan that measures blood flow]) can be used for diagnosis. Blood bile acids are elevated after a meal, so the before-meal and after-meal bile acid levels are compared. Despite the variety of tests available, a confirmed diagnosis may not be available until surgery is done.