Felis ISSN 2398-2950

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.

Sampling

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