It is not uncommon to be presented with an older cat that has been losing weight. Weight loss is a cardinal sign for concern in geriatric patients. Although there are many possible causes common ones in cats are:

  • Chronic Renal Failure
  • Hyperthyroidism
  • Neoplasia


In Chronic Renal Failure there is often a change in appetite and thirst. The appetite is often variable but overall decreased. Owners report that their pet has become finicky and it is hard to second-guess what they will want to eat. They think they have just found the flavor/brand that they like and they get picky again. They also report that there is an increase in thirst. The stools are often very firm and dry yet they have to clean the litter box more frequently due the increase in urination.

On physical exam these cats tend be dehydrated and have a poor coat quality. Their faces often have a pinched look. The temperature may be lower than normal. Abdominal palpation often reveals a colon with firm fecal nuggets, a full bladder and smallish kidneys with a lumpy feel.

Blood tests and a urinalysis will confirm a suspicion of renal problems.

On the blood tests the BUN and Creatinine are elevated. Potassium may be on the low side; Phosphorous and Amylase may be elevated. There may also be evidence of anemia without regeneration of red blood cells. Dehydration is evident in many cases.

The urinalysis will exhibit a low specific gravity and increased protein levels. Urinary tract infections are frequently detected.

Treatment of these cases is directed at support of the body in face of a failing organ system. The condition is progressive and the level of support is determined by the clinical and laboratory findings.

The kidney is an active and selective pump system of the body. When working correctly it can conserve or eliminate body fluids. On a hot day if little fluid is consumed the kidney will pass very little liquid onto the bladder for elimination. On the other hand, if one consumes a lot of fluid…such as Beer at the pub…then there much fluid presented to the bladder for elimination. The failing kidney loses its ability to selectively conserve or eliminate fluid based on the body’s needs. Too much fluid is lost to the bladder. Thus the cat drinks excessively in an attempt to correct the situation. Unfortunately it cannot take in enough fluid orally and so continues to dehydrate despite increasing its fluid intake. The healthy kidney is also actively selective in eliminating waste products and conserving building blocks. In failure this ability is lost, waste products accumulate and required substances/elements are lost. It is this functional loss of selectivity and dehydration that leads to illness in renal failure. In addition there are cells in the kidneys that determine when one needs to produce more red blood cells to replace those that grow old and die. In chronic renal failure these cells cannot function and without the stimulus to produce more red cells anemia develops.

Treatment in renal failure is aimed at countering/minimizing the effects of ongoing compromised renal selectivity and cellular function. Minimally the diet is changed to specially formulated diets that lower the build up of toxic waste products and provide supplementation for substances lost through the failing kidney. Most cats require fluid supplementation and B vitamin support. This is often administered by subcutaneous (just beneath the skin) injections of a balanced electrolyte solution plus injectable and/or oral B vitamins. The volume and frequency is determined by each individuals needs. Even if serum (blood) Potassium levels are not low, tissue levels are usually inadequate. Thus an oral Potassium supplement can be given daily. As the organ failure progresses toxic waste products can lead to ulceration of the mouth and gastrointestinal tract. Products such as oral Famotidine can be given to help reduce these toxic effects. Oral phosphorous binders are indicated in cats with elevated Phosphorous levels. The build up of waste products and inappropriate electrolyte levels, combined with dehydration, lead to progressive inappetence. Appetite can be artificially stimulated with the use of oral appetite stimulants. In cats that have serious nonregenerative anemia parenteral medications can be used to stimulate red cell production. However these products can be costly and have the potential for significant side effects. The use of herbs and acupuncture have long been used to help support kidney deficient patients. Oral products based based on TCM principles are now available to help manage renal patients. Also available are oral products that may lower the level of Blood Urea Nitrogen that accumulates in animals with renal deficiency.

Thus although we can’t yet reverse the renal issues we can manage them and slow their progress making the kitties feel better for a longer period of time.



In Hyperthyroidism the appetite is usually very good and there is no evidence of an increase in thirst( unless the kitty has renal failure as well). Often the cat has a pinched look to its expression. These cats are usually very active and are often described as restless. Weight loss can be marked even though eating well. On examination a thyroid nodule may be palpable in the region of the ventral neck. The heart rate is usually elevated and murmurs are often detected.

Blood tests reveal elevated thyroid hormone level and often elevated liver enzymes.

Hyperthyroidism is due to an overactive thyroid producing excess amounts of thyroid hormone. This excess leads to an increase in metabolism. This results in weight loss, an elevated heart rate and often an increase in blood pressure. These cardiovascular changes can lead to anatomical changes in the heart itself.

Treatment is aimed at lowering the circulating levels of thyroid hormone. Appropriate treatment can truly cure, rather than just control/respond to, this condition.

Several treatment options are available. The preferred choice for any specific case depends on the overall physical condition of the pet, availability of the procedure, the veterinarians preference and owners financial situation. In the past surgical removal of one or both thyroid glands was a common approach. However this requires a general anaesthesia in a cat that already has cardiovascular compromise and can also result in damage to the associated parathyroid gland. Antithyroid drugs such as Methimazole can be administered orally on a daily basis to control thyroid levels. Most, but not all, cats tolerate this drug well but severe side effects can occur. As dose requirements vary from patient to patient periodic blood tests must be run to ascertain the dose is correct. The drug is not expensive but must be given continuously on a daily basis. If cost is not a major concern then the treatment of choice is Radioactive Iodine (I131). This is administered as a single subcutaneous injection. The hyperactive thyroid tissue is painlessly destroyed and the healthy tissue continues to function normally. It truly is a cure for this condition. Another option to consider if I131, or medication, is not an option is to feed Hills Prescription Y/D as the only food source and water s the only fluid source. This diet is iodine deficient and without adequate iodine the production of thyroid hormone is reduced. This diet only works if it is the sole food source. It is not an option for kitties with access to the great outdoors where they can supplement their diets with small rodents and birds.

It must be remembered when treating a hyperthyroid cat that cardiac changes may also need to be addressed. If after the heart rate and blood pressure return to normal a heart murmur or abnormal rhythm persists then a cardiac work-up will be required. In some cases irreversible heart damage occurs and it in itself must be treated. In addition some hyperthyroid cats, especially those with elevated blood pressures, may have underlying chronic renal failure unmasked when the metabolism returns to normal. Thus it is wise to have repeat blood tests run sometime after the thyroid condition is reversed.


Weight loss, without evidence of either of the above conditions, may be due to Neoplasia (growths/tissue infiltrates)…benign or malignant. A careful physical examination, blood tests, radiographs and ultrasound are useful in determining the presence of Neoplasia. However, in many cases it is not easy to detect until the process is quite advanced.

Thus in many, though not all, cases weight loss in the elderly cat can be managed if not cured. If your cat…elderly or not…exhibits unexplained weight loss have him/her examined by a veterinarian.