Biochemical tests for diabetes

2021-07-05 03:11 PM

HbA1C is the conjugated form of glucose with HbA1, It makes up more than 70 percent of glycosylated hemoglobin. HbA1C levels correlate with blood sugar levels

The WHO has defined: Diabetes (diabetes) is a disease in which the fasting blood sugar is greater than 7.0 mmol/l (126 mg/dl), when the blood sugar is tested more than twice, or the blood sugar is measured. at any time is greater than 11 mmol/l.

To diagnose diabetes, people usually do some of the following tests:

Measurement of blood glucose

Normal: the blood glucose concentration of a healthy, fasting person is: 4.4 - 6.1 mmol/l (0.8-1.1 g/l).

In the past, Folin-Wu blood glucose determination was a non-specific quantitative method based on the reducing property of sugar, so when the patient's blood has other reducing agents (eg vitamin C), it will produce results. The result is higher than the actual sugar concentration.

Currently, specific blood glucose quantification is the enzyme-color method. It is a method of measuring blood sugar based on the catalyzed reaction of glucosidase: the oxidation of glucose to gluconic acid and peroxide hydrogen (H2O2). H2O2 reacts with 4-amino antipyrine and phenol under the catalysis of peroxidase (POD) to form a pink substance, quinone imine, and water. Measuring the optical density of quinone imine red at 500 nm will calculate the blood glucose result.

By enzyme method, blood sugar results are more accurate, independent of reducing substances in the blood like the classical method (Folin-Wu), so the results are usually a bit lower than the Folin-Wu method.

Detection of urinary tract and ketones

When testing 10 urine parameters, the results showed:


Urinary glucose (-).

Ketonuria (-).

Normal urine pH is in the range of 5-8.

Diabetic diseases:

Urinary tract (+), sometimes the urinary glucose concentration is greater than 1000mg/dl (>10 g/l).

Ketonuria (+).

Urine pH drops sharply because the ketone bodies are all strong acids (acetoacetic acid and β-hydroxybutyric acid). When the ketone bodies are elevated in the blood, they are excreted in the urine, causing the urine pH to drop lower than normal (pH < 5).

Urinary density (d):

Can vary from 1.01 to 1.02 for the average person. . Elevated in diabetes (d > 1,030).

Oral hyperglycemia test

Hyperglycemia or glucose tolerance testing is used to help diagnose diabetes.

Tests to cause hyperglycemia include:

Intravenous glucose tolerance test: used less often because of the psychology of having to draw blood many times, not as simple as the oral method.

Oral glucose tolerance test (OGTT): this is a simpler, easier test that still gives reliable diagnostic results.

How to proceed:

Prepare the patient:

Do the test in the morning after 10-16 hours of fasting (0.15g glucide/1 kg body weight), no alcohol, no smoking, complete rest during the test. Do not test during recovery for acute illness, stress, surgery, trauma, pregnancy, immobilization for chronic patients. For hospitalized patients, it is necessary to stop some drugs that affect blood sugar levels several weeks before the test. Examples: oral diuretics, phenytoin, oral contraceptives.

The test is used in patients with mildly elevated blood sugar (6.1-7.8 mmol/l).

Not indicated for the following diseases:

Hyperglycemia is markedly (> 7.8 mmol/l) and persistent.

Frequently, the blood sugar is not markedly increased (< 6.1 mmol/l).

The patient has clinical symptoms of typical diabetes and blood glucose > 11.1 mmol/l.

In pregnant women with suspected diabetes (it is best for them to wait until after giving birth, if necessary, test at 6-7 weeks of pregnancy).

Secondary diabetes mellitus (inherited diabetic syndrome, hormone-induced hyperglycemia).

Give the patient 1.75 g (in 4.4 ml of water) per kg of body weight. Before giving oral glucose, have the patient urinate completely and retain 5 ml of this urine, number the sample 0 hours, and draw blood with the numbered blood sample 0 hours. Give the patient a glucose solution to drink, when it is finished, start counting time after 1/2, 1, 2, and 3 hours of drinking glucose to take blood and urine for glucose quantification and quantification.

Thus, taking blood and urine tests from time to time:

0h: 1st time.

30': second time.

60' : 3rd time.

180': 4th time.

Result evaluation:


Glucose/0h < 6.1 mmol/l (blood sugar in the normal range).

After 30-60 minutes: the peak blood glucose concentration can reach <9.7 mmol/l.

After 120 minutes: return to concentration < 6.7 mmol/l.

Diabetes: if blood glucose after 30 - 60 minutes rises higher than the same time in normal people and the time to return to the original level can be 4-6 hours (much slower than normal people).

In clinical practice, in addition to blood glucose and urine tests, people also do quantitative tests of fructosamine, HBA1C. These tests allow monitoring of treatment and disease prognosis because they reflect blood glucose levels over a longer period of time.

Insulin tolerance test

Intravenous insulin at a dose of 0.1 units/kg body weight. Use lower doses in patients with hypopituitarism.

Normal: fasting blood sugar drops rapidly, up to about 50% of baseline value after insulin; Blood sugar decreases for about 20-30 minutes, then gradually increases to the initial value in about 90-120 minutes.

Increased insulin tolerance: blood sugar drops by 25% and returns to baseline quickly, seen in diabetes.

Figure: Line showing the test causing hyperglycemia in normal people and diabetic patients.

a) Normal.

b) Renal threshold.

c) Diabetes.

Blood fructosamine

Blood fructosamine is the amount of sugar present in the complex of glucose with albumin according to the formula:

Albumin + Glucose = Fructosamin

Fructosamine allows the assessment of blood glucose levels at about 2 to 3 weeks after stabilizing treatment in diabetic patients.

Changes in fructosamine concentrations are associated with changes in plasma albumin or protein levels.

The fructosamine test is more valuable than the blood sugar test in that:

Fructosamine not only shows blood sugar levels at the moment but also shows how stable the person's blood sugar was from the previous 2 weeks.

In the normal person:

Fructosamine = 2,4- 3,4 mmol/l.

HbA1C (Hemoglobin glycosylate)

HbA1C is the combination of glucose and HbA1. It accounts for more than 70% of glycosylated hemoglobin. HbA1C levels correlate with blood glucose levels during flare-ups (approximately 6-8 weeks) and thus provide a wealth of information about hyperglycemia or hyperglycemia.

Hb = HbA1 (97- 98%) + HbA2 (2-3%) + HbF (< 1%).

HbA1 + Glucose = HbA1C ( > 70% Hb glycosyl ) HbA1 + G6P = HbA1b.

HbA1 + FDP = HbA1a.

Currently, to diagnose diabetes, people usually do three tests:

Blood glucose.

Glucosuria, ketones in the urine.

Oral hyperglycemia test.

Insulin and Fructosamine tolerance tests require more technology and equipment, so small and medium-sized hospitals often do less.