Ron Hines DVM PhD
The Cholesterol Level In Your Dog And Cat’s Blood
Cholesterol is one of several fatty substances (lipids) that circulate in your pet’s blood. Much that is found there was made in its liver (then bound or “packaged” to Low or High Density Lipoproteins to keep it in solution, so it remains dissolved in the blood stream). Some is esterified(into a storage form); much that isn’t esterified (the free cholesterol) eventually leaves your dog or cat’s body thorough its bile in the form of bile acids – only to be reabsorbed by its intestines in a never-ending cycle.
Besides making cholesterol in their liver, dogs and cats also absorb cholesterol from their food and produce a bit in other body organs including their intestines. How much that adds to their circulating blood cholesterol is a matter of debate.
The other major fatty substances (lipids) in circulation is triglyceride. Both cholesterol and triglycerides tend to go up, or down in tandem. Read about the causes of high triglyceride levels in dogs and cats here.
The test tube at the right top of this page has too much lipid. However, creamy white serum like that is probably due to its high triglyceride level – not its high cholesterol level.
As cholesterol circulates in your pet’s blood, it acts as a building block for steroid hormones, bile ingredients (bile acids), cellular membrane synthesis and vitamin D production. All body cells also manufacture some cholesterol on their own. So, cholesterol is a critical and necessary molecule in the function of all cells in your pet’s body.
Abnormally high or low cholesterol levels in dogs and cats can be a hint in identifying health problems, but, in itself, high or low cholesterol does not diagnose any specific disorder. When it is found, your pet has hyperlipidemia (more specifically, hypercholesterolemia). Elevated blood cholesterol levels are considerably more common in dogs than cats.
Most veterinarians prefer to assay cholesterol and triglyceride levels in your pet after a suitable period of time has passed since its last meal. That appears to be more important when obtaining a valid triglyceride level than its cholesterol level – but a fasting blood sample from your pet is still preferred.
Unlike in us humans, high circulating cholesterol levels in our pets rarely cause heart and blood vessel disease. Both dogs and cats are carnivores that seem to have adapted well to a diet high in saturated animal fat – a rich source of cholesterol. However, a cholesterol concentration (> 750 mg/dL) can be associated with a risk of atherosclerosis – even in dogs and cats (most of those pets will be dogs and most will turn out to have hypothyroidism).
A high blood cholesterol level is not thought to cause many symptoms in our pets (a whitish lipid line does occasionally appear at the margins of the cornea in some hypothyroid dogs. (read here) But in general, finding a high cholesterol level in your dog or cat just means that further tests need to be performed to locate any underlying endocrine gland or metabolic disease. When none can be found, the treatment is to modify the pet’s diet (restrict their fat intake to the minimum adequate amount) and, perhaps, as a last resort, (cautiously), use some of the cholesterol-lowering drugs designed for humans.
Reasons Your Pet’s Blood Cholesterol Level Might Be Elevated (Hypercholesterolemia):
High Cholesterol Level After A Recent Meal = Postprandial Hypercholesterolemia
After-eating (postprandial) cholesterol levels will be higher in your pet than in blood samples taken some time later (a fasting blood sample). How long a meal elevates cholesterol is quite variable. The elevation can last from 2 to as long as 10 hours. However, the increase in your pet’s blood cholesterol level due to a meal is rarely large. Although higher than it would have been, it will rarely be above the highest normal range for a cat or a dog.
Hypothyroidism = A Sluggish Thyroid Gland
Low thyroid hormone levels are the most common pathological (worrisome) cause of high cholesterol (and high triglyceride) levels in dogs. Hypothyroidism is very rare in cats. In dogs, both LDL and HDL increase. The deficiency in the thyroid hormone, T3, in hypothyroidism decreases LDL cholesterol uptake, raising the pet’s blood cholesterol level.
About 75% of hypothyroid dogs have an abnormally high fasting cholesterol levels (about 88% have abnormally high blood triglycerides). Read more about hypothyroidism in dogs here. Occasionally, a puppy will be born a dwarf. It is common for dwarf puppies to have been born with hypothyroidism and to have abnormally high cholesterol levels. (read here)
Cushing’s Disease = Overactive Adrenal Glands =hyperadrenocorticism
Cushing’s disease is primarily seen in dogs. It involves the excess production of cortisol by your pet’s adrenal glands. You can read about the disease here. One side effect of the excess cortisol is damaged and swollen liver cells (hepatocytes), that can no longer process cholesterol properly. Some believe that the excess cortisol also stimulates lipase activity and cholesterol production. In that situation, mild to moderate increases in blood cholesterol and triglycerides often occur (in over 50% of the cases).
Prolonged or Excessive Use of Corticosteroid Medications
Corticosteroid medications mimic your pet’s natural cortisol. So, the effect of those drugs will be the same as that of Cushing’s disease.
Poorly controlled Diabetes
Sudden or recurring bouts of pancreatitis in dogs have been associated with elevated blood cholesterol levels (although a more consistent finding in pancreatitis is higher than normal blood triglyceride levels). It is unclear if the high levels of either are the cause or the result of the pancreatitis, but in that situation, one of their fat-digesting enzymes does not function correctly (lipoprotein lipase).
In cats, this situation is more complex because few cats have simple pancreatitis. Most cats with pancreatic problems have them as part of triad disease, a condition that also affects their liver and gall bladder. About 70% of those cats will have elevated blood cholesterol levels.
Late in chronic or recurrent pancreatitis, the pet’s pancreas can lose its ability to produce digestive and absorptive enzymes (exocrine pancreatic insufficiency =EPI). At that stage, blood cholesterol levels are often low because fatty substances can no longer be absorbed from the pet’s diet.
Many forms of liver disease can be responsible for higher than normal blood cholesterol levels in dogs and cats. Some of those are short-term problems of inflammation due to infectious agents or toxic exposure (eating or being exposed to toxic products). Others are cases of long term chronic forms of hepatitis. In some, the increased cholesterol levels are due to increased liver cholesterol formation, in others, less of the cholesterol that is formed is able to leave the body through the pet’s bile (like cholestasis, the next cause I mention). Despite that explanation, many cases of chronic liver disease eventually result in lower than normal blood cholesterol levels when the liver eventually loses its ability to manufacture cholesterol.
Cholestasis/Cholangitis = Blockages To The Flow Of Bile From Your Pet’s Liver To Its Intestine
This problem is also called extra-hepatic biliary duct obstruction (EHBDO). It occurs in dogs and cats and one common sign is abnormally high blood cholesterol levels. I mentioned that much of your pet’s cholesterol eventually leaves it body through the bile. If that flow of bile is obstructed (blocked), either by a gallstone obstructing the pet’s bile duct, inflammation in the area, infection, cancer or in any other way; that cannot happen. In cats, it is common for the pet’s liver to be affected as well (cholangiohepatitis). In all those situations, the pet’s cholesterol level can be high.
I mentioned earlier that the corticosteroid medications, often given to pets for a variety of health problems, can cause high cholesterol levels (= iatrogenic Cushing’s disease).
Methimazole (Tapazole®, Felimazole®) and a similar medication, carbimazole, both given to hyperthyroid cats, can cause blood cholesterol levels to be abnormally high (probably through its effects on the liver, since liver enzymes like ALT often go up as well).
High Fat Diets And Obesity
High fat diets elevate the triglyceride level of otherwise healthy pets; but how much they contribute to a dog or cat’s blood cholesterol level is uncertain. Some studies suggest it does. (read here) Also, the possible heart benefits of a low cholesterol diet in humans does not appear to carry over to our dogs and cats.
There are other dangers in trying to keep normal dogs or cats on a “low cholesterol” diet. If you replace animal fat with cholesterol-free vegetable oil, such as olive oil, it will take five time the amount to meet the pet’s linoleic acid needs.
But there are still so many good reasons to keep your pet trim: To delay or avoid osteoarthritis, obesity-related kidney disease, pancreatitis, cancer, urinary incontinence, and even tracheal collapse in tiny dog breeds. So don’t neuter pets too young – it encourages obesity (read here), feed appropriate amounts (no matter how much your pet begs !) and encourage moderate exercise for your pet to avoid a sedentary lifestyle. Remember, neutered dogs and cats require about 25-30% fewer calories than they did when unneutered, to stay trim.
If your veterinarian can find no pathological (disease-related) causes for high cholesterol levels in your dog or cat; first try a lower-fat, lower-calorie diet (fed in an amount appropriate for your pet’s size). If that is not sufficient, a diet high in sugar beet pulp has proven helpful in reducing cholesterol and triglyceride levels in many dogs (up to 10% wt reduction). Some find a human fish oil supplement helpful as well (0.5 g/10 lb = 0.5g/4.5 kg body weight daily).
In the few dogs with underlying genetic causes for their high cholesterol, medications designed to lower cholesterol levels in humans have been tried. All must be used cautiously, none are approved for pets and all seem to produce considerably more side effects in pets than people (lethargy, diarrhea, muscle pain, and liver damage).
A few pets are just born with a tendency to high blood cholesterol and triglycerides (primary or inherited hypercholesterolemia or dyslipidemia). Miniature schnauzers seem particularly prone to a form of this problem (idiopathic hyperlipidemia). But similar problems have also has been seen in Briards, Rottweilers, Shetland Sheepdogs Beagles, Miniature Poodles, Cocker Spaniels and Dobermans. It is also a rare problem in cats that have a deficiency in the fat-digesting enzyme, lipase (hyperchylomicronemia, feline familial hyperlipidemia).
It is often a good idea to start by following the diet recommendations I gave for obese pets in general when pets with these genetic causes are overweight (when their serum triglyceride >500 mg/dL or their cholesterol >750 mg/dL, your veterinarian may resort to lipid-lowering medications as well).
Most veterinarians will try to get your pet’s fasting triglyceride level below 400 mg/dL. Without treatment, persistently high cholesterol/triglyceride (hyperlipidemia) can lead to pancreatitis, diabetes mellitus, and, perhaps, contribute to kidney injury.
Soft coated wheaten terriers suffer from a number of chronic maladies that affect their kidneys and intestines (but the problem has also been seen in Bernese Mountain Dogs and Labrador and Golden Retrievers). (read here)
Female dogs appear more at risk than males. This problem can seriously affect one or the other organ – or both. When the dog’s kidneys are affected, the condition is called protein-loosing nephropathy (PLN). The symptom the various forms this disease can take include weight loss, diarrhea, vomiting, weakness, decreased appetite, edema, allergic skin disease and increased drinking and urination.
When kidney PLN signs predominate, dogs often have a low blood albumin level, a low globulin level and higher than normal cholesterol level. In serious cases, their BUN and Creatinine levels are high (= kidney failure = azotemia).
This disease has many forms and stages. In some dogs, intestinal protein loss (protein losing enteropathy or PLE)can actually causes the dog’s blood cholesterol to be low).
Cats and dogs of all breeds can have kidney damage similar to what occurs in those Wheatens. These cases are called nephritic syndrome. They are often triggered by long term inflammatory, autoimmune or infectious diseases that can affect any part of their body. Cancer can also be the underlying cause.
Through complex mechanisms, these pets often develop kidney damage (glomerulonephritis or amyloidosis) that cause their kidneys to leak blood proteins into their urine. These pets commonly develop edema or ascites due to their low blood protein levels and their kidney’s inability to regulate their blood electrolytes. Many of these pets also have elevated blood cholesterol levels (read here)
When your dog or cat is overweight and your veterinarian has eliminated other possible explanations for its high blood cholesterol level, a diet change could be in order.
Reasons Your Pet’s Blood Cholesterol Level Might Be Low (Hypocholesteroemia)
Dogs and cats that receive inadequate amounts of food (starvation), those that will not eat and those on a very low-fat diet can have depressed blood cholesterol and triglyceride levels.
Dogs and cats that have problems absorbing nutrients (malabsorption/maldigestion problems) also can have low blood cholesterol. The problems underlying their inability to absorb fats usually relate to their pancreas or chronic intestinal inflammation such as IBD.
There are other pets that have lost the capacity to manufacture cholesterol in their liver. So chronic or sudden liver disease of various types sometimes results in low blood cholesterol levels. You can read about some of the causes of liver disease in dogs and cats here.
Chronic inflammation anywhere in your dog or cat’s body can liberate inflammatory cytokines that lower cholesterol levels. Read through the DxMe pages on c-reactive protein and fibrinogen to learn about some of those conditions.
Chronic Pancreatitis = Exocrine Pancreatic Insufficiency = EPI
Long term pancreatic issues can make your pet’s cholesterol level go up or down. Your dog or cat’s pancreas has two intertwined portions, the exocrine portion that produces digestive enzymes and the endocrine portion that produces insulin and various other messenger compounds.
Dogs and cats with chronic pancreatitis often lose the ability to produce sufficient lipase to absorb cholesterol and other fats from their food. At that stage of the disease (exocrine pancreatic insufficiency or EPI) their cholesterol levels can be low. (read here)
Chronic Intestinal Disease
The walls of continuously inflamed small intestines tend to lose their ability to hold back blood proteins and leak them into the intestinal space. The condition is called protein-losing enteropathy (PLE). In those situations, the pet’s blood albumen drops due to loss of blood albumen and sometimes their cholesterol levels will be low as well (hypocholeserolemia).
In cases of low cholesterol due to PLE, liver and kidney causes can usually be ruled out with a bile acid and microalbuminuria test. The Alpha1-Proteinase Inhibitor (α1-PI) test or an intestinal biopsy are also good ways to confirm the presence of PLE.
Protein loosing enteropathy can be part of the genetically based kidney and intestinal problems that are occasionally seen in soft coated wheaten terriers.
A Decline In General Health = Cachexia
Some dogs inherit a genetic tendency toward low blood cholesterol levels.
Hyperthyroidism = An Overactive Thyroid Gland
Cats with hyperthyroidism can have low blood cholesterol levels. Hyperthyroidism is exceedingly rare in dogs. The only cases I know of were in dogs that were fed raw beef thyroid glands.
Addison’s Disease = Hypoadrenocorticism
One of the many lab value abnormalities seen in Addison’s disease in dogs can be a low blood cholesterol level. Read about Addison’s Disease here. Addison’s disease is a condition that is often misdiagnosed on the first, second and even third try (“The Great Imitator”). Its signs are so easily for us veterinarians to confused with dietary indiscretions, liver disease, kidney disease, pancreatic tumors (insulinoma), or chronic intestinal disease (the PLE discussed earlier). Diagnosis requires an ACTH stimulation test.
Abnormal Liver Blood Circulation = portosystemic Shunts or Hepatic Microvascular Dysplasia
An abnormal routing of blood – either acquired or inherited (portosystemic shunts – a rather rare condition) can also cause blood cholesterol levels in pets to be low. Approximately 62% of the dogs with this problem and 67% of the cats have lower than normal blood cholesterol levels.
Dogs and cats receiving phenobarbital or primidone for epilepsy can develop low cholesterol levels – perhaps due to these drug’s negative effect on the liver. In those cases, the pet’s liver enzymes are almost always abnormal as well.
Besides the general health decline (cachexia) that tumors can produce, some of them cause normal body cells to take up more cholesterol (up regulation of LDL-receptors). This can cause blood cholesterol levels to drop. Pro-inflammatory cytokines might be involved in the process too – it is still poorly understood.
Histiocytic Sarcoma Complex
Histiocytes are white blood cells that have left the blood and dwell in body tissue (macrophages derived from monocytes and dendritic cells). They remain part of the pet’s immune system. These cells occasionally “morph” into tumors in dogs, for reasons that remain unknown. Some of these tumors are limited to the skin, some disappear spontaneously, but some become true malignancies. In those cases, the pet’s blood work is usually quite abnormal, their thrombocyte count, blood albumin and cholesterol levels tend to be low.
The problem is seen most frequently in Bernese Mountain Dogs, but Golden and Flat Coated Retrievers, Rottweilers, Irish Wolfhounds and Shar Peis can be affected as well.
Immune Mediated Diseases = Lupus-like Syndromes
Pets with autoimmune disease sometimes have abnormal blood cholesterol levels due to the disease’s variable effect on many different body organs. Depending on the organs most affected and the stage of the disease, the pet’s cholesterol levels can be high or low.
Intestinal Phosphorus Binding Agents
Dogs and cats in kidney failure usually have abnormally high blood phosphorus levels. So, they are often given oral medications called phosphorus binding agents to slow the absorption of phosphorus from their food. One of those agents, sevelamer HCl (Renagel®) is known to cause low cholesterol levels.
Complementary Tests That Come To Mind:
CBC/WBC and blood chemistry profile, including serum total protein and albumin levels, and blood triglyceride level, Free T-4 level, bile acids, ACTH stimulation test (if Addison’s Disease is suspected), Low Dose Dexamethasone Suppression test (if Cushing’s disease is suspected). See my links to specific diseases that cause cholesterol levels to be abnormal for some suggestions on other blood tests.
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