7.1 Procedural Definition: What Is This Test About?

Whole blood glucose can be a very useful window into a patient’s metabolic state. Numerous diseases are associated with changes in whole blood glucose concentration. Determination of whole blood glucose is used both diagnostically and in monitoring the response to therapy. Handheld glucometers allow a rapid patient‐side determination of whole blood glucose concentration and are especially useful when evaluating a patient with history and clinical findings suggestive of diabetes mellitus, Cushing’s disease, liver disease, sepsis, or neurologic disease involving either seizures or changes in mentation.

7.2 Procedural Purpose: Why Should I Perform This Test?

Glucose is the primary source of energy for cellular metabolism and one of the few clinical chemistry tests that can be considered a true STAT test, especially in a patient with seizures or altered mentation. With the onset of reliable in‐house handheld glucometers, this test can be easily performed on a small amount of whole blood for both diagnosis and monitoring of patients with altered metabolic needs.

Whole blood glucose concentration can be altered by many pathophysiological mechanisms including increased or decreased metabolic consumption, decreased or increased production, and decreased glycogen stores. Many disorders of glucose metabolism are the result of changes in hormone activity. The primary hormones involved in glucose metabolism are insulin (decreases blood glucose), glucagon (increases blood glucose). Diabetes mellitus is common in both dogs and cats and depends on the identification of persistent hyperglycemia with glucosuria. In addition, high circulating concentrations of glucocorticoids, catecholamines, and growth hormone can oppose the activity of insulin (insulin antagonists) increasing blood glucose concentration in stressed or excited patients. Decreased circulating glucocorticoids can result in hypoglycemia by increasing peripheral insulin sensitivity and inhibiting gluconeogenesis.

Since the liver is a primary site for storage of glucose in the form of glycogen and production of glucose by gluconeogenesis or glycogenolysis, loss of greater than 75% of liver mass can result in hypoglycemia. Starvation‐induced hypoglycemia is rare in the adult dog and requires severe depletion of glycogen stores and protein as a source of amino acids for gluconeogenesis. In contrast, young animals, especially toy breeds, have a higher frequency of hypoglycemia associated with starvation or hyporexia. This is due to their limited glycogen storage and reduced capacity for gluconeogenesis. One of the most common abnormalities seen in starvation is decreased urea nitrogen rather than hypoglycemia. See Chapter 8 for evaluation of whole blood urea nitrogen using in‐house test strips.

Sepsis, due to the production of inflammatory cytokines that are insulin antagonists, is also associated with alterations in blood glucose concentration. Both hyperglycemia and hypoglycemia can be seen with sepsis depending on the time frame of the disease. Acute sepsis is often associated with increased circulating corticosteroids and catecholamines resulting in hyperglycemia. As the septic process proceeds, depletion of hepatic glycogen stores, decreased hepatocyte gluconeogenesis, and decreased insulin clearance by the liver result in the development of hypoglycemia. As with all clinical pathology data, blood glucose should be interpreted within the context of the patient and other laboratory data.

Whole blood glucose is required when evaluating any patient with clinical history or physical exam findings suggestive of diabetes mellitus, such as polyuria, polydipsia, weight loss (especially in the face of a good appetite), hyporexia, chronic inflammatory, or infectious disease, such as chronic urinary tract infections, and cataracts. Both in clinic and at home monitoring of whole blood glucose is essential when following a patient with diabetes mellitus [1]. Since stress and excitement can alter blood glucose concentration, teaching a client how to use a handheld glucometer to perform glucose monitoring in a less stressful environment for the patient is not uncommon. Given adequate guidance and training, most owners can perform a glucose curve at home when needed to assist in evaluating a patient’s insulin needs. As with all tests, it is important to assure that the owner understands and uses a standard protocol and maintains proper recording of the results.

Glucose is the primary source of energy for maintenance of neuronal activity. The brain requires a constant source of glucose to maintain normal function and mentation. Any patient with altered mentation, ataxia, weakness, convulsions, or seizures should have a blood glucose concentration determination done. It is important to remember that a rapid drop in blood glucose concentration will result in acute clinical signs at a higher blood glucose concentration than is seen when there is a gradual decrease. It is difficult to predict clinical signs based on a single blood glucose value, clinical history, and other physical findings are important factors in the interpretation of blood glucose.

Urine glucose evaluation is important in evaluating the underlying cause of hyperglycemia. Stress or excitement induced hyperglycemia may or may not be associated with glucosuria. The hyperglycemia of stress and excitement are transient and usually not sufficiently high to exceed the renal tubular glucose reabsorption threshold except in the cat. When hyperglycemia and glucosuria are present concurrently along with the appropriate history and physical exam findings, a diagnosis of diabetes mellitus is warranted. Hyperadrenocorticism can result in or exacerbate diabetes mellitus due to insulin antagonism and should be considered in a patient that appears refractory to appropriate insulin therapy (insulin resistant). Glucosuria without hyperglycemia can occur when there is proximal renal tubular injury or a hereditary defect in renal tubular transport mechanisms (Fanconi’s syndrome).

Currently, there are several handheld glucometers available for use in veterinary medicine with some variation in accuracy. In one study, the AlphaTrak 2^® and OneTouch were shown to have the best performance [2]. Hematocrit may have an effect on glucose values. In this study, comparing a human glucometer and a glucometer for use in veterinary medicine (AlphaTrak2^®), the veterinary glucometer had the best performance in samples with a hematocrit that is within reference interval or higher [3]. While there is an expectation that the glucose concentration from a glucometer should correlate with the glucose concentration obtains from a reference laboratory, they will not be the same. The concentrations should, however, result in the same clinical interpretation of hypoglycemic, euglycemic, or hyperglycemic based on each instrument’s reference intervals. In most studies comparing glucometers to other instruments used in reference laboratories, when there is a difference in interpretation, it is usually because the glucose concentration obtained from the glucometer is lower, resulting in the interpretation of hypoglycemia versus euglycemia or euglycemia versus hyperglycemia [2].

7.3 Equipment

• Handheld in‐house glucometer for use in veterinary patients
  
• Reagent strips within the expiration date
  
• Recommended whole blood sample type (see instrument manual for list of appropriate sample types)
  
• Syringe or lancet for collection of a fresh venous blood sample
  
• Whole blood in a blood collection tube containing approved anticoagulant (see instruction manual for appropriate anticoagulants)
  
• Standard operating procedure or instrument manual

7.4 Procedural Steps: How Do I Perform This Test?

This procedure is for using whole blood collected in ethylenediaminetetraacetic acid (EDTA) and describes the general steps for glucometers. Each glucometer will have a specific protocol in the instruction manual, which should be closely adhered to when performing a glucose determination.