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Blood biochemistry: glucose
Overview
- Physiological plasma levels of glucose are maintained by glucagon (raises glucose) and insulin (lowers glucose) to ensure that a continuous supply of glucose is available as an energy source for cell metabolism.
- Absorbed via the small intestine, glucose is stored as glycogen in liver and muscle and liberated when plasma levels fall.
- Other hormones can raise plasma glucose by increasing gluconeogenesis or glycogenolysis or increasing/decreasing utilization.
- Any condition which affects these hormones will influence plasma glucose levels.
- Hypoinsulinism (diabetes mellitus Diabetes mellitus) → hyperglycemia.
- Cortisol, adrenaline, growth hormone, progesterone, xylazine → increase glucose levels.
Uses
Alone
- Diabetes mellitus Diabetes mellitus.
- Insulin overdose (Somogyi effect) in diabetes mellitus.
In combination
- Glucose tolerance test Glucose tolerance test: for diabetes mellitus when glucose levels are consistently elevated but not at diagnostic level.
- Insulin assay Insulin assay: for insulinoma Insulinoma (insulin-secreting tumor of pancreatic beta cells) - rare in the cat.
- Fructosamine or glycosylated hemoglobin to assess mean glucose concentration status over last 2-3 weeks, or 4-8 week, respectively.
Other points
- A recent meal and stress can raise blood glucose levels above normal range.
- Convulsions can elevate blood glucose.
Sampling
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Tests
Methodologies
Screening
- Dextrostix used with whole blood only; gives a semiquantitative indicator of gross changes in plasma glucose.
Specific assays
- 3 glucose specific enzyme methods commonly in use:
- Glucose oxidase (GO).
- Herokinase (HK).
- Glucose dehydrogenase (GD).
- Glucose oxidase reaction - results said to approach true glucose value under reliable laboratory conditions (used in glucose specific urine test strips).
- Ortho-toluidine - also measures galactose and mannose, but these are considered insignificant; simple, fast test.
Non-specific assays
- Nelson-Somogyi and Folin-Wu - may give slightly higher than true levels, the former more specific than the latter.
- Ferricyanide - approaches true glucose level.
Availability
- Widely available.
Technique intrinsic limitations
- Some laboratory methods affected by presence of enzyme inhibitors/activators.
- Glycolysis by erythrocytes estimated to reduce glucose concentration by approximately 10% per hour at room temperature.
- Prompt separation of serum/plasma from cells, and refrigeration, will reduce glycolysis.
Result Data
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Further Reading
Publications
Refereed papers
- Recent references from VetMedResource and PubMed.
- Martin G J W et al (1999) Food intake and blood glucose in normal and diabetic cats fed ad libitum. J Fel Med Surg 1 (4), 241-251.
- Steiner J M & Bruyette D S (1996) Canine Insuloma. Comp Cont Educ Prac Vet 18 (1), 13-24.
- Plotnick A N (1995) Diagnosis of diabetes mellitus in dogs and cats, contrasts and comparisons. Vet Clin North Am Small Anim Pract 25 (3), 563-570.
Other sources of information
- Ettinger S J & Feldman E C (2000) Eds. Textbook of Veterinary Internal Medicine. 5th edn. W B Saunders & Co, USA.
- Kaneko J J, Harvey J W & Brass M L (1997) Eds. Clinical Biochemistry of Domestic Animals. 5th edn. Academic Press, USA.
- Feldman E C & Nelson R W (1996) Canine and Feline Endocrinology. 2nd edn. W B Saunders & Co, USA.
- Bonagura J D & Kirk R W (1995) Eds. Kirk's Current Veterinary Therapy XII. Small Animal Practice. USA.
- Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa University Press, USA.