Diabetes

Diabetes is caused by hyperglycaemia. There are two types:

• Type 1 or insulin-dependent diabetes mellitus, which is caused by the destruction of ß cells in the islets of Langerhans in the pancreas. Its aetiology can be very diverse (hereditary, pancreatitis, trauma, etc.). The destruction of ß cells causes the pancreas to stop producing insulin. Insulin levels do not increase when glucose is administered. This is the most common type of diabetes in dogs, and it is incurable.
• Type 2 or non-insulin-dependent diabetes mellitus, which is caused by the decreased sensitivity of target cells (liver, musculoskeletal system, etc.) to insulin secreted by ß cells. Over time, type 2 diabetes can progress to type 1. It is the most common type in cats, and can be cured.

There is also a third type of diabetes, called iatrogenic or type 3 diabetes, which is caused by an increase in gluconeogenesis due to the administration of drugs such as glucocorticoids, progesterone, glucagon, or growth hormone.

Symptoms

Polyuria, polydipsia (only appear after onset of glucosuria), polyphagia, and weight loss. Common symptoms in dogs are blindness due to cataract formation and hepatomegaly due to hepatic lipidosis. If diabetes progresses, it can be complicated by ketoacidosis and its associated symptoms, such as tachypnoea, weakness, dehydration, vomiting, and diarrhoea. Despite losing weight, the animal is usually obese. In cats, a plantigrade stance when walking can be observed, caused by diabetic neuropathy.

Interpretation of laboratory tests

General Tests

• Blood biochemistry
  1. Glucose reference values:
     • Dogs: 55 - 110 mg/dL
     • Cats: 60 - 170 mg/dL

A glucose level over 130 mg/dL (in dogs) is considered hyperglycaemia. GLU < 200 mg/dL accompanied by polyuria and polydipsia, suggests another diagnosis (Cushing's, diestrus, hyperglycaemia medication, ethylene glycol poisoning).
Diabetes can be confirmed if:

• • • Dogs: GLU > 200 mg/dL with symptoms.
    • Cats: GLU > 280 mg/dL with symptoms.

Signs appear when GLU exceeds the kidney threshold and there is evidence of glucosuria. In practice, this occurs when blood glucose levels exceed 180-200 mg/dL in dogs and 280-300 mg/dL in cats.
Is very important to bear in mind that one reason for increased glucose levels can be stress.

1. 2. GPT reference values:
      • Dogs: 10 to 50 IU/L.
      • Cats: 10 to 59 IU/L.

GPT levels are increased.

1. 3. BUN and CRE reference values:
      • Dogs: BUN - 6 to 50 mg/dL;
        CRE- 0.6 to 2 mg/dL.
      • Cats: BUN - 14 to 48 mg/dL;
        CRE- 0.8 to 2 mg/dL.

If the animal is dehydrated, BUN levels will be increased, but not CRE.

• Urine biochemistry: Glucosuria
  If tests show ketoacidosis, ketonuria, proteinuria and leukocyturia may develop.
  In diabetes, hyperglycaemia is always associated with glucosuria. If there is evidence of one but not the other, the diagnosis may be flawed. Hyperglycaemia without glucosuria is often due to environmental stress on the animal or the sampling process itself (increased adrenaline secretion). In cats, this stress can even lead to glucosuria.
  If glucosuria without hyperglycaemia is detected, the cause may be primarily kidney-related.
  If it is unclear whether the animal is stressed or not, the owner can collect the urine sample in a more relaxed environment and take it, refrigerated, to the centre as soon as possible.

Specific tests

• Insulinaemia
  This test is recommended to determine the type of diabetes.
  1. Normal values: 5 - 25 μU/mL.
  2. Far lower values (1- 2 μU/mL) indicated type 1 diabetes mellitus.
  3. Normal or slightly elevated values: Type 2 diabetes mellitus in non-obese (or healthy) animals.
  4. Extremely elevated values: Type 2 diabetes mellitus in obese animals.

If the sample has been haemolyzed or if the serum or plasma is not promptly separated from the blood cell, the values will be artificially decreased.
In general, hyperglycaemia with hypoinsulinaemia is a sign of type 1 diabetes mellitus and hyperglycaemia with hyperinsulinaemia is a sign of type 2 diabetes mellitus.

• Fructosamine Shows glucose levels over the preceding 1 to 3 weeks. If glucose levels are very elevated (> 450 mg/dL), fructosamine can increase in as little as 5 to 8 days in dogs and 3 to 7 days in cats. It does not show occasional stress-induced increases in glucose (< 90 min). Fructosamine levels decrease after about one week after glucose levels have normalized.
  It may be useful in diagnosing diabetes mellitus in cats that present continuous but moderate increases in glucose that are not diagnostic.
  1. Reference values:
     • Dogs - 260-340 μmol/L
     • Cats - 220-340 μmol/L
  2. Value > 340 μmol/L usually indicate diabetes mellitus.
• Glucose challenge test. Contact the laboratory.

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