Causes of glucose rise and fall

In a number of conditions, blood glucose levels increase (hyperglycemia) or decrease (hypoglycemia).

Most often, hyperglycemia develops in patients with diabetes mellitus. Diabetes mellitus can be diagnosed with a positive result of one of the following tests:

• clinical symptoms of diabetes mellitus (polyuria, polydipsia and unexplained weight loss) and a random increase in plasma glucose concentration ≥11.1 mmol/L (≥200 mg%), or:
• fasting plasma glucose concentration (no food intake for at least 8 hours) ≥7.1 mmol/L (≥126 mg%), or:
• plasma glucose concentration 2 hours after an oral glucose load (75 g glucose) ≥11.1 mmol/l (≥200 mg%).

The diagnostic criteria for diabetes mellitus and other categories of hyperglycemia recommended by WHO (Report of WHO Consultation, 1999) are given in Tables 4–16. For epidemiological or screening purposes, a single fasting glucose result or a 2-hour glucose result after an oral glucose load is sufficient. For clinical purposes, the diagnosis of diabetes mellitus should always be confirmed by repeat testing on a subsequent day, except in cases of undoubted hyperglycemia with acute metabolic decompensation or obvious symptoms.

According to the new recommendations, the following fasting venous plasma glucose concentrations have diagnostic value (WHO recommends using only venous plasma test results for diagnosis):

• the normal fasting plasma glucose concentration is up to 6.1 mmol/l (<110 mg%);
• fasting plasma glucose concentration from 6.1 mmol/l (≥110 mg%) to 7 (<128 mg%) is defined as impaired fasting glycemia;
• A fasting plasma glucose concentration of more than 7 mmol/l (>128 mg%) is regarded as a preliminary diagnosis of diabetes mellitus, which must be confirmed using the above criteria.

Diagnostic criteria for diabetes mellitus and other categories of hyperglycemia

Category	Glucose concentration, mmol/l
	Whole blood		Blood plasma
	Venous	Capillary	Venous	Capillary
Diabetes mellitus:
On an empty stomach	>6.1	>6.1	>7.0	>7.0
120 minutes after glucose intake	>10.0	>11.1	>11.1	>12.2
Impaired glucose tolerance:
On an empty stomach	<6.1	<6.1	<7.0	<7.0
120 minutes after glucose intake	>6.7 and <10.0	>7.8 and <11.1	>7.8 and <11.1	>8.9 and <12.2
Impaired fasting glucose:
On an empty stomach	>5.6 and <6.1	>5.6 and <6.1	>6.1 and <7.0	>6.1 and <7.0
120 minutes after glucose intake	<6.7	<7.8	<7.8	<8.9

In addition to diabetes mellitus, hyperglycemia is possible in the following conditions and diseases: damage to the central nervous system, increased hormonal activity of the thyroid gland, cortex and medulla of the adrenal glands, pituitary gland; brain injuries and tumors, epilepsy, carbon monoxide poisoning, strong emotional and mental arousal.

Hypoglycemia can be caused by the following reasons.

• Long-term fasting.
• Impaired absorption of carbohydrates (stomach and intestinal diseases, dumping syndrome).
• Chronic liver diseases due to impaired glycogen synthesis and a decrease in the liver's carbohydrate depot.
• Diseases associated with impaired secretion of counter-insular hormones (hypopituitarism, chronic adrenal cortex insufficiency, hypothyroidism).
• Overdose or unjustified prescription of insulin and oral hypoglycemic drugs. In patients with diabetes mellitus receiving insulin, the most severe hypoglycemic conditions, up to hypoglycemic coma, usually develop with a violation of the diet - skipping meals, as well as vomiting after eating.
• Mild hypoglycemic conditions may occur in diseases that occur with so-called "functional" hyperinsulinemia: obesity, mild type 2 diabetes mellitus. The latter is characterized by alternating episodes of moderate hyperglycemia and slight hypoglycemia 3-4 hours after eating, when the maximum effect of insulin secreted in response to the alimentary load develops.
• Sometimes hypoglycemic conditions are observed in individuals with CNS diseases: widespread vascular disorders, acute pyogenic meningitis, tuberculous meningitis, cryptococcal meningitis, encephalitis in mumps, primary or metastatic tumor of the pia mater, nonbacterial meningoencephalitis, primary amoebic meningoencephalitis.
• The most severe hypoglycemia (except for cases of insulin overdose) is observed in organic hyperinsulinism due to insulinoma or hyperplasia of the beta cells of the pancreatic islets. In some cases, the blood glucose level of patients with hyperinsulinism is less than 1 mmol/l.
• Spontaneous hypoglycemia in sarcoidosis.