Page 136 - Clinical Small Animal Internal Medicine

104 Section 2 Endocrine Disease

brain but also by the renal medulla, red blood cells, and Box 13.1 DAMN IT diagnosis mnemonic
VetBooks.ir insulin‐sensitive tissues, such as muscle) exceeds the D = Degenerative or Developmental
sum of glucose delivery into the circulation (from
ingested carbohydrates and hepatic and renal glucose
production). A = Anomalous or Autoimmune
M = Metabolic, Mechanical, or Mental
N = Nutritional or Neoplastic
I = Inflammatory, Infectious, Ischemic, Immune‐
Clinical Signs of Hypoglycemia mediated, Inherited, Iatrogenic, or Idiopathic
T = Traumatic or Toxic
Clinical hypoglycemia is a blood glucose level low
enough to cause symptoms, including impairment of a list of differential diagnoses are given using the acro­
brain function. For example, values below 50 mg/dL nym DAMN IT scheme for diagnosis (Box 13.1).
(2.8 mmol/L) are often accompanied by symptoms, but
values below the lower end of the normal reference
range may not be. Hence clinical hypoglycemia, which is Artifactual Hypoglycemia
also referred to as “the hypoglycemic syndrome,” is
not defined by hypoglycemia alone, but according to Artifactual hypoglycemia, also called pseudohypoglyce­
Whipple’s triad – hypoglycemia accompanied by symp­ mia, is not a clinical syndrome but rather a result of arti­
toms that are relieved by the administration of glucose or factually low blood glucose concentration in vitro, mainly
by feeding. in the presence of leukocytosis, polycythemia, or both.
Symptoms of hypoglycemia are categorized as neuro­ In dogs, it has been reported that the glucose concentra­
glycopenic (lack of glucose supply to the brain) or auto­ tion in whole blood kept at room temperature can
nomic (largely the result of the sympathoadrenal decrease by as much as 10 mg/dL/h. Presumably, this
discharge triggered by hypoglycemia). The neuroglyco­ decrease in glucose concentration is due to continuing
penic signs range from lethargy, weakness, ataxia, and utilization of glucose by cells present in the blood.
unusual behavior to seizures and coma. Clinical signs Therefore, whole blood obtained for glucose determina­
resulting from stimulation of the sympathoadrenal sys­ tion should be centrifuged within an hour after collec­
tem include restlessness, muscle tremors, and hunger. tion, separated and refrigerated or frozen to minimize
Clinical manifestations are dependent on the duration artifactual lowering of blood glucose concentration. In
and severity of hypoglycemia. For example, in healthy addition, the practice of measuring glucose in whole
people, symptoms of hypoglycemia develop at a mean blood immediately after collection using portable hand‐
plasma glucose concentration of 55 mg/dL. However, held glucometers specifically designed and manufac­
people with recurring fasting hypoglycemia appear to tured for measuring human blood glucose, while quick
tolerate low blood glucose levels (e.g., <40 mg/dL) for and convenient, is less accurate than measurements by
prolonged periods without exhibiting clinical signs. This an accredited veterinary laboratory. Because dogs, cats,
adaptive process to chronic severe hypoglycemia also and humans have different ratios of glucose between the
occurs in animals. plasma and red blood cells, if a portable hand‐held glu­
cometer is used to determine the blood glucose, it is rec­
ommended to use the AlphaTRAK® glucometer (Abbott
Etiology/Pathophysiology Animal Health) which is calibrated specifically for dogs
and cats.
Another cause of artifactual hypoglycemia is labora­
Identification of randomly obtained or a fasting blood tory error. Incorrect values can occur with any assay
glucose concentration below 60 mg/dL is cause for and therefore, it is always wise to confirm a finding
concern in dogs or cats. Although this finding is not of hypoglycemia by evaluating another blood sample
always diagnostic of organic disease, normal dogs before more sophisticated or extensive studies are
and cats have consistently been shown not to have performed.
blood glucose concentrations decline below this level. Other less common causes of pseudohypoglycemia are
Therefore, once artifactual hypoglycemia has been seen with the following conditions.
ruled out as a possible cause, organic disease is a likely
cause of persistent hypoglycemia. Failure in any one of ● Leukemias (e.g., chronic lymphocytic leukemia) and
the key steps in the production or conservation of glu­ benign forms of leukocytosis (e.g., leukemoid reactions).
cose may result in hypoglycemia and clinical signs of ● Chronic hemolytic anemia accompanied by a high
hypoglycemia. The many causes of hypoglycemia and (>3%) nucleated red blood cell count.