Clinical significance

The primary aim of laboratory diagnosis is to assess the carbohydrate metabolism impairment in diabetes mellitus, including the following:
1) determination of glucose concentration in fasting blood and demonstration of postprandial glycosuria; and
2) assessment of glucose tolerance.

Fasting glucose concentration.

 Capillary bloodSerum or plasmaUnit
Reference values< 5.55< 6.38mmol/L
Borderline area5.55 – 7.226.38 – 8.33mmol/L
Pathologic area> 7.22> 8.33mmol/L
Lowest value2.22 – 2.78< 2.5mmol/L

Normal values of fasting blood glucose do not exclude an impairment, because many patients with diabetes mellitus may have fasting blood glucose within the reference range. Therefore, the blood glucose concentration is determined 2 hours after the last meal. In healthy individuals, the concentration of blood glucose at 2 hours postprandially will be within the reference range. If the glucose value is normal at 2 hours postprandially, a carbohydrate metabolism impairment can most probably be excluded. The findings falling within the borderline or pathologic area should be repeated on several occasions before making a definite diagnosis.
The World Health Organization (WHO) criteria for the diagnosis of carbohydrate metabolism disturbances are presented in Table.

WHO criteria for the diagnosis of diabetes mellitus

DiagnosisSampling timeGlucose concentration (mmol/L)
Whole bloodPlasma / serum
Normalfasting < 5.6< 6.4
Diabetes mellitusfasting> 6.7> 6-7> 7.8
at 2 hours of glucose load > 10.0> 11.1> 11.1
Impaired glucose tolerancefasting< 6.7< 6.7< 7.8
at 2 hours of glucose load6.7 – 10.07.8 - 11.17.8 - 11.1

Diseases associated with hyperglycemia

Diabetes mellitus
Diabetes mellitus develops due to complete or relative insulin deficiency. It rarely occurs after an irreversible lesion of the endocrine part of the pancreas or due to enhanced action of insulin antagonist hormones. It usually develops as a primary disease. According to WHO classification, there are two types of the disease.

Main types and characteristics of diabetes mellitus

CharacteristicIDDM (Insulin dependent diabetes mellitus)NIDDM (Non-insulin dependent diabetes mellitus)
Typical onsetchildhood
young age
middle age
old age
Type of onsetacutegradual
Constitutional typeleanobese
Weight lossusualrare
Proneness to ketosisusualunusual
Serum insulin levellow or absentusually normal
Familiar occurrence of diseaserarecommon

Insulin deficiency leads to impairment in the metabolism of carbohydrates as well as of lipids and protein. The disease severity depends on the grade of metabolic disturbance. Fasting hyperglycemia occurs in case of major insulin deficiency, and glycosuria develops when glucose concentration exceeds renal threshold (>10 mmol/L).

1) Physiologic variations in serum glucose concentration
An increase in serum/plasma glucose between 9 and 10 a.m., 2 and 3 p.m. and after 6 p.m. probably is a transient response of the body to the respective meals.
A) Increased fasting glucose concentration consequential to the increased adrenaline level in the circulation in:
• hard physical activity,
• strong emotions, e.g., fear.
B) Decreased fasting glucose concentration:
• normal pregnancy (mild hypoglycemia),
• severe hypoglycemia occurs in normal neonates born to diabetic mothers.
• within 2-4 hours postnatally, blood glucose falls to the lowest level, returning to the birth value in 3-5 days

2) Pathologic changes in serum glucose concentration

Increased glucose concentration in:Decreased glucose concentration in:
• acromegaly,
• acute myocardial infarction,
• acute pancreatitis,
• acute renal failure ,
• adrenal cortical hyperfunction,
• bacterial meningitis,
• bacterial pneumonia,
• burn,
• carcinoma of the pancreas ,
• cholelithiasis,
• chronic pancreatitis,
• chronic renal failure,
• congestive cardiac failure,
• diabetes mellitus,
• diabetic acidosis,
• ectopic pregnancy,
• essential hypertension,
• hemochromatosis,
• hepatolenticular degeneration,
• hyperlipoproteinemia type III and IV,
• hyperthyroidism,
• intestinal obstruction,
• pancreatic cyst and pseudocyst
• pheochromocytoma,
• septicemia,
• shock,
• traume.
• acute and subacute necrosis of the liver,
• acute arthritis (pyogenic),
• adrenal cortical hypofunction,
• benign neoplasm of pancreas,
• biliary cirrhosis,
• cancer of liver,
• cholangitis,
• congestive heart failure ,
• erythroblastosis fetalis,
• Forbes’ disease,
• hepatic failure.
• hypoglycemia (non-specific).
• hypothyroidism,
• Laennec’s or alcoholic Cirrhosis,
• liver abscess (pyogenic),
• liver cirrhosis,
• McArdle’s disease,
• peptic ulcer,
• pre-eclampsia,
• subacute thyroiditis,
• toxic hepatitis,
• von Gierke’s disease.