Testing for Low Blood Sugar

What might be causing my pet’s low blood sugar?

Low blood sugar, or low blood glucose, is called hypoglycemia (hypo = low + glyc = sugar + emia = in the blood). Hypoglycemia is caused by many different conditions and some of them are quite serious. A few examples include:

• Severe liver disease
• Congenital portosystemic liver shunts in puppies
• Hypoadrenocorticism (Addison's disease)
• Severe bacterial infection (sepsis)
• Inadequate nutrition in kittens and toy-breed puppies
• Extreme exertion (seen in hunting dogs and high-performing sport dogs)
• Over-treatment (too much insulin) of diabetes mellitus, also called sugar diabetes
• Some types of tumors, especially a tumor of the pancreas, called an islet cell tumor or insulinoma
• Xylitol toxicity from ingesting certain sugar-free foods (e.g., gum, candies, peanut butter) 

What are the signs of low blood sugar?

The typical signs of low blood sugar (hypoglycemia) include weakness, collapse, disorientation, tremors, and sometimes seizures.

Can a laboratory result showing low blood sugar sometimes be wrong?

Yes. If a blood sample is not handled properly after collection, glucose can be lost from the sample and the test result may be falsely low. This sampling error occurs because red blood cells naturally consume glucose, and they continue to use glucose even in a collected blood sample if steps are not taken to prevent this. 

If a pet is healthy and has no signs of hypoglycemia (weakness, collapse, etc.) a laboratory report showing a low blood glucose value may be inaccurate due to sampling error. The blood glucose test should be repeated using a fresh blood sample. If the repeated glucose value is normal and the pet still has no signs of hypoglycemia, then the initial value was likely incorrect, and no further investigation is needed.

How do we determine the cause of a pet’s low blood sugar?

Finding the cause of a pet's low blood sugar usually starts with a complete history and physical examination. A pet's history of illness includes details about changes in activity or attitude, appetite and water intake, bowel function and urine output, or other changes an owner may have noted. If a pet is receiving insulin injections for diabetes, the history would also include any problems an owner might be having in giving the injections.

"A complete physical examination may give clues about the cause of low blood sugar."

A complete physical examination may give clues about the cause of low blood sugar. For example, the presence of jaundiced (yellow) gums suggests underlying liver disease; the presence of a fever might indicate an underlying infection; the presence of an abdominal mass could signal a tumor.

History and physical examination are very important, but further testing will likely be necessary. Your veterinarian may recommend doing screening tests. These are a series of simple tests that provide information about the overall health of your pet and may provide further clues about the underlying problem. They include complete blood count (CBC), serum biochemistry profile, and urinalysis. 

What might the screening tests indicate?

Based on the results of these screening tests, additional tests may be recommended.

Complete Blood Count (CBC)

This simple blood test provides information about the different cell types in blood, including red blood cells, which carry oxygen to the tissues; white blood cells, which fight infection and respond to inflammation; and platelets, which help the blood to clot. The CBC provides details about the number, size, and shape of the various cell types and identifies the presence of abnormal cells in circulation. In a pet with hypoglycemia, changes seen on a CBC could include:

• Anemia. This means the number of red blood cells and the amount of hemoglobin in the blood are lower than normal. Anemia can be found with many diseases, including those causing hypoglycemia (e.g., Addison's disease, liver disease, or cancer).
• Changes in the shape of red blood cells. Certain types of oddly shaped red blood cells are seen in hypoglycemic pets that have conditions such as liver disease, severe infection, and a portosystemic shunt, which is a blood vessel abnormality found in puppies and kittens.
• High numbers of white blood cells with an increased proportion of immature white blood cells. This is a sign of severe underlying infection and can be associated with hypoglycemia.
• Unusual pattern of white blood cells. The presence of high numbers of lymphocytes and eosinophils (types of white blood cells) in a blood sample is unusual and could be a sign of underlying Addison's disease, which is associated with hypoglycemia.

Serum biochemistry profile

Serum biochemistry profile refers to the chemical analysis of serum (the liquid part of blood). There are many substances in serum, including proteins, enzymes, fats, sugars, hormones, and electrolytes. Measuring the levels of the various substances in the blood provides information about the health of the body's organs and tissues including the liver, kidney, and pancreas, and helps to detect diabetes.

In a pet with hypoglycemia, examples of changes seen on a serum biochemistry profile could include:

• Abnormally high levels of the liver-related enzymes alanine aminotransferase (ALT), alkaline phosphatase (ALP), and gamma glutamyltransferase (GGT). These changes are associated with liver damage and might explain a pet's hypoglycemia.
• Low glucose. Together with low cholesterol, low albumin (a blood protein), and low urea (a product of protein metabolism), low glucose suggests severe, chronic liver disease, as well as portosystemic shunts in puppies and kittens.
• Altered electrolytes. Electrolytes are salts and minerals found in the blood. Changes in electrolytes, especially sodium and potassium, are often seen with Addison's disease, which can cause hypoglycemia.

Urinalysis

A urinalysis tests the chemical and physical characteristics of urine. Urinalysis is important in any sick animal and is necessary for the proper interpretation of the serum biochemistry profile, especially in a pet that has kidney disease or diabetes. In a pet with hypoglycemia, examples of changes seen on urinalysis could include:

• Specific crystals called ammonium biurate crystals. These are strongly associated with portosystemic shunts and other types of severe liver disease.
• Large numbers of white blood cells and white blood cell casts (tubular-shaped clusters of white blood cells). These suggest serious underlying bacterial infection of the kidneys.
• Large amounts of glucose. In a pet known to have diabetes mellitus, the presence of large amounts of glucose in the urine suggests the disease is poorly controlled.

What if all the tests results are normal except for low blood sugar?

If the serum biochemistry profile confirms a pet has low blood glucose, and no other abnormalities can be found, then the hypoglycemia may be due to an underlying tumor called an insulinoma. This is a tumor of the insulin-producing cells of the pancreas and causes excessive amounts of insulin to be released into the blood stream. Insulin is the hormone responsible for removing glucose from the blood.

In a pet with an insulinoma, the excess insulin causes too much glucose to be removed from the blood and blood glucose levels fall dangerously low. Affected animals show clear signs of hypoglycemia, including seizures.

What additional tests might be recommended in a pet with hypoglycemia?

There are several additional tests that might be recommended, depending on the results of a pet's history, physical examination, and screening tests. Examples of more advanced tests include:

• Serum bile acid testing. If severe liver disease or a portosystemic shunt is suspected, then measurement of serum bile acids is recommended.
• X-rays and ultrasound. These imaging studies are used to assess the liver and other abdominal organs, especially if liver disease, insulinoma, or other tumors are suspected.
• Biopsy followed by microscopic examination is recommended if a tumor or abnormal organ is found on imaging. The biopsy might be collected by fine needle aspiration, ultrasound-guided biopsy, or surgical intra-operative biopsy.
• ACTH stimulation test is recommended if Addison's disease is suspected.
• Blood culture is recommended if widespread bacterial infection (sepsis) is suspected. Blood culture confirms the presence of bacteria in the bloodstream and determines which antibiotic should be used treat the infection.
• The simultaneous measurement of blood insulin and blood glucose levels may help to confirm the presence of an insulinoma. Paired insulin and glucose testing can be done at referral laboratories. If blood sugar is low, then insulin levels should be low to low-normal as the body’s normal response to avoid hypoglycemia. When insulinoma is present, insulin levels are unregulated by this feedback mechanism and will be elevated with concurrent hypoglycemia. Typically, imaging studies and possibly biopsy would be recommended to confirm the diagnosis.