Differential diagnosis of tumour-associated hypoglycaemia in small animals (abstract)

Authors: Thompson JC
Publication: New Zealand Veterinary Journal, Volume 42, Issue 2, pp 77, Apr 1994
Publisher: Taylor and Francis

Animal type: Cat, Companion animal, Dog
Subject Terms: Clinical pathology, Diagnostic procedures, Glucose/glycogen, Metabolic disease, Disease/defect, Endocrine/autocrine/paracrine, Neoplasia, Oncology
Article class: Abstract

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Abstract: While there are a number of causes of hypoglycaemia in small animals, many of these may be ruled out on the basis of clinical signs, history, age and other laboratory results. Further tests for diagnosis include insulin measurements, the glucagon tolerance test and glucose administration tests. For the diagnosis of insulinomas (β cell tumours) in dogs, serum insulin and glucose concentrations may be measured at the same time and put into the amended insulin to glucose ratio (AIGR), which is reportedly the most accurate method of diagnosis. The ratio provides an indication of whether or not the serum concentration of insulin is appropriate for the concentration of glucose. The value of this ratio in cats is not known because there are so few reports of insulinomas in this species. In cats it may be better to simply compare insulin and glucose levels to see if they are appropriate. The occasional false-positive AIGR has been reported in dogs with other tumours and severe sepsis, but with these conditions the insulin is usually also low. Insulin to glucose and glucose to insulin ratios may also be calculated but are considered less useful than the AIGR. The glucagon tolerance test is considered less accurate than the AIGR but may be used instead of, or in addition to, the AIGR if results of the AIGR are equivocal.
The pathogenesis of the hypoglycaemia in non-insulinoma tumours is not known. It may be due to either increased usage of glucose by the tumour or to altered hormonal control. In the veterinary literature, hypoglycaemia has been associated with a number of tumours including hepatomas and hepatocellular carcinomas. In a dog with a hepatoma in which both hypoglycaemia and low insulin concentration were obtained, a glucagon tolerance test showed that blood glucose concentration in the affected dog fell more slowly than in a control dog. In a cat with a hepatoma, blood glucose rose and fell at about the same rate as in a control cat and secretion of insulin appeared to be inhibited. Somatomedins (insulin-like growth factors) and/or somatostatin secretion have been suggested as possible causes for the hypoglycaemia in these cases but further work needs to be done on future cases. In humans with tumour-associated hypoglycaemia, elevated serum somatomedin concentrations have been measured with a variety of tumour types. This suggests that in some tumours there is altered hormonal control of glucose.

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