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Blood Glucose Estimation

Q.1-What is the level of Fasting blood glucose in normal health?

Answer- Fasting blood glucose (FPG) is measured after an overnight fast of 10 hrs. (1) FPG 7.0mmol/L (126 mg/dL) warrants the diagnosis of Diabetes Mellitus (DM).

Q.2- What is Random blood Glucose? What is its significance?

Answer-Random is defined as without regard to time since the last meal. Random Blood Glucose (RBG) measurement is required only during emergency. The current criteria for the diagnosis of DM emphasize that the FPG is the most reliable and convenient test for identifying DM in asymptomatic individuals. A random plasma glucose concentration >11.1 mmol/L (200 mg/dL) accompanied by classic symptoms of DM (polyuria, polydipsia, weight loss) is sufficient for the diagnosis of DM.

Q.3- What is the difference between Post load blood glucose and postprandial blood glucose?

Answer-Post load blood glucose means blood glucose level 2 hours after a glucose load as it is done in Oral glucose tolerance test. Post prandial means blood glucose 2 hours after a normal meal.

Q.4- Why is plasma sample preferred over serum sample for estimation of blood glucose?

Answer- Plasma has the advantage over serum since the blood can be immediately added to a mixture of anticoagulant and preservative and can be processed immediately. If serum is used, there is a delay in processing the sample since it takes nearly 20-30minutes for the serum to get separated from the blood and in that span some glucose is metabolized by anaerobic glycolysis and falsely low levels are obtained. Hence on practical grounds plasma is a preferred choice over serum.

Q.5- What is the purpose of adding preservative to the blood sample(collected for estimation of blood glucose) before processing?

Answer- Red blood cells possess glycolytic enzymes; hence glucose disappears fairy rapidly due to glycolysis from the whole blood. Glucose loss takes place approximately at a rate of 0-5 mmol/L/hour and it completely disappears within 6 hours. So blood is collected in to an anti glycolytic and anticoagulant mixture to get the accurate results.A fluoride and oxalate mixture (20 mg/5ml) in the ratio of 1:3 is used to prevent glucose loss. Sodium fluoride acts as a preservative since by acting as an inhibitor of Enolase enzyme, it inhibits the conversion of 2-phospho glycerate to phosphoenol pyruvate. Hence glycolysis is inhibited and glucose loss of the sample is prevented. Oxalate (Potassium oxalate) acts as an anticoagulant.

Q.6- What is the reason that for a given volume, the level of whole blood glucose is always lower than that of plasma glucose?

Answer-Water content of plasma is more than whole blood for a given volume and it has more dissolved glucose. Water content of red blood cells is 73% as compared to 93% of plasma.To convert from whole-blood glucose, multiplication by 1.15 has been shown to generally give the serum/plasma level.

Q.7- What are the conditions causing hyperglycemia?

Answer-The common conditions causing hyperglycemia are as follows-

i) Diabetes Mellitus

ii) Insulin Resistance

iii) Diabetes prone states– Gestational Diabetes, Impaired fasting glycemia, Impaired glucose tolerance    

iv) Diseases of the exocrine pancreas– cystic fibrosis, hemachromatosis, fibrocalculous pancreatopathy, pancreatitis, pancreatectomy, neoplasia,   

v) Endocrinopathies—Acromegaly, Cushing’s syndrome,glucagonoma, pheochromocytoma, hyperthyroidism, somatostatinoma, aldosteronomas

vi) Drug- or chemical-induced—Nicotinic acid, glucocorticoids,thyroid hormone, β -adrenergic agonists, thiazides,phenytoin etc.

vii) Genetic syndromes causing hyperglycemia—Down’s syndrome,Klinefelter’s syndrome, Turner’s syndrome, Wolfram’s syndrome, Friedreich’s ataxia, Huntington’s chorea, Laurence-Moon-Biedl syndrome, myotonic dystrophy,Porphyria, Prader-Willi syndrome

viii) Stress

ix) Chronic infections

Q.8- What are the common causes of Hypoglycemia?

Answer-Hypoglycemia is a laboratory ‘diagnosis’ which is usually considered a blood glucose level below 60 mg/dL. Symptoms begin at plasma glucose levels in the range of 60 mg/dL and impairment of brain function  occurs at approximately 50 mg/dL. The common causes of hypoglycemia are as follows-

1) Physiological- Prolonged fasting or starvation

2) Pathological-

i) Drugs -especially insulin, sulfonylureas, ethanol sometimes quinine, rarely Salicylates,sulfonamides, others.

ii) Critical illnesses– Hepatic, renal, cardiac failure or sepsis

iii) Hormone deficiencies- Cortisol, growth hormone, or both ,Glucagon and epinephrine (in insulin-deficient diabetes)

iv) Endogenous hyperinsulinism


vi) Insulin secretagogue (sulfonylurea, other)

vii) Ectopic insulin secretion

viii) Alimentary (Postgastrectomy)

ix) Hereditary fructose intolerance, Galactosemia

x) Glycogen Storage diseases

Q.9-What are the indications for performing glucose tolerance test?

Answer-If the fasting plasma glucose level is 126 mg/dL or higher on more than one occasion, further evaluation of the patient with a glucose challenge is unnecessary. However, when fasting plasma glucose is less than 126 mg/dL in suspected cases, a standardized oral glucose tolerance test may be done.

75 g of glucose dissolved in 300mL of water is given after an overnight fast to a person who has been receiving at least 150–200 g of carbohydrate daily for 3 days before the test. The data is interpreted as follows-

Normal Glucose Tolerance

Impaired Glucose Tolerance

Diabetes Mellitus

Fasting plasma glucose (mg/dL)

< 110



Two hours after

glucose load

< 140



*The Diabetes Expert Committee criteria for evaluating the standard oral glucose tolerance test.

For proper evaluation of the test, the subjects should be normally active and free from acute illness.Medications that may impair glucose tolerance include diuretics, contraceptive drugs, glucocorticoids, niacin, and phenytoin should be avoided on that day.

The common indications for Glucose Tolerance Test are as-

a) Family history of diabetes mellitus

 b) Typical Symptoms but normal biochemical profile

 c) Abnormal biochemical profile but no symptoms

 d) History of gestational diabetes mellitus

 e) History of large for size babies at the time of delivery

Q.10- What is the advantage of estimating Glycated hemoglobin over fasting blood glucose?

Answer- Glycated hemoglobin (HbA1c)comprises 4–6% of total hemoglobin A1.The hemoglobin A1c fraction is abnormally elevated in diabetic persons with chronic hyperglycemia.Since glycohemoglobins circulate within red blood cells whose life span lasts up to 120 days, they generally reflect the state of glycemia over the preceding 8–12 weeks, thereby providing an improved method of assessing diabetic control. Fasting blood glucose on the other hand is affected by many factors like meals, stress, infections and drugs,hence a true glycemic status can not be ascertained.

Q.11- What is meant by self monitoring of blood glucose?

Answer-Capillary blood glucose measurements performed by patients themselves, as outpatients, are extremely useful. In type 1 patients in whom”tight” metabolic control is attempted, they are indispensable. There are several paper strip (glucose oxidase, glucose dehydrogenase, or hexokinase methods for measuring glucose on capillary blood samples. A reflectance photometer or an amperometric system is then used to measure the reaction that takes place on the reagent strip.

Q.12- Apart from estimation of blood glucose, what are the other investigations to be carried out for the diagnosis of diabetes mellitus?

Answer- The laboratory investigations for the diagnosis of Diabetes mellitus are as follows-

1) Urine Analysis– shows Glucosuria, Ketonuria and Microalbuminuria

2) Blood Biochemistry includes Blood glucose estimation and apart from that the other tests are-

i) Glycated hemoglobin

ii) Serum fructosamine

iii) Lipid profile

iv) Plasma insulin

v) c-peptide

vi) Islet cell antibodies

3) Additional Tests– In addition to the standard laboratory evaluation, the patient should be screened for DM-associated conditions (e.g., kidney, liver and thyroid dysfunction).

Q.13- If the blood glucose is lower than 60 mg/dL, as in case of Starvation, what kind of abnormal compounds will be excreted in urine in excess?

Answer- Urine will have ketone bodies in excess, but glucose will not be there. In states of glucose deprivation, fatty acids are largely oxidized and the product acetyl coA is channeled towards ketogenesis. Ketone bodies are also used as alternative fuel molecules.

Q.14- What is the most important cause of hypoglycemia in Diabetes Mellitus?

Answer- One of the therapeutic goals of diabetes is to decrease blood glucose levels in an effort to minimize the development of the long term complications of the disease. However, appropriate dosage is difficult to achieve in all patients, and hypoglycemia caused by excess insulin is the most common complication of insulin therapy, occurring in more than 90 % of the patients. The frequency of hypoglycemic episodes, coma and seizures is particularly high with intensive treatment regimens designed to achieve tight control of blood glucose. In normal individuals, hypoglycemia triggers a compensatory secretion of counterregulatory hormones, most notably glucagon and epinephrine, which promote hepatic production of glucose. However patients with type 1 diabetes also develop a deficiency of glucagon secretion.This defect occurs early in the disease and is almost universally present four years after diagnosis. These patients thus rely on epinephrine secretion to prevent severe hypoglycemia. However as the disease progresses, type 1 diabetes patients show diabetic autonomic neuropathy and impaired ability to secrete epinephrine in response to hypoglycemia. The combined deficiency of glucagon and epinephrine secretion creates a condition sometimes called “Hypoglycemia unawareness”. Thus patients with long standing diabetes are particularly vulnerable to hypoglycemia. Hypoglycemia can also be caused by strenuous exercise. Exercise promotes glucose uptake into muscles and decreases the need for exogenous insulin. Patients should therefore check blood glucose levels before or after intensive exercise to prevent or abort hypoglycemia.

Q.15- What is meant by “Honeymoon period” in diabetes mellitus?

Answer- Around ¼ of all patients who get type 1 diabetes develop what is known as a ‘honeymoonperiod within days or weeks of the onset of treatment. It is as if the patient has gone into remission and it can be confusing for the patient as it would appear that the condition has corrected itself. Some patients actually require no insulin during this phase and this may last for weeks or months. It is usually best to keep treating with insulin even if the requirements are negligible, to avoid possible insulin allergy upon re-exposure and also to maintain a treatment regimen and not give false hope to the patient.

Q.16- What is the significance of non diabetic Glycosuria?

Answer- Non diabetic Glycosuria(renal Glycosuria) is a benign asymptomatic condition wherein glucose appears in the urine despite a normal amount of glucose in the blood, either basally or during a glucose tolerance test. Its cause may vary from an autosomally transmitted genetic disorder to one associated with dysfunction of the proximal renal tubule (Fanconi’s syndrome, chronic renal failure), or it may merely be a consequence of the increased load of glucose presented to the tubules by the elevated glomerular filtration rate during pregnancy. As many as 50% of pregnant women normally have demonstrable sugar in the urine, especially during the third and fourth months. This sugar is practically always glucose except during the late weeks of pregnancy, when lactose may be present.

Q.17- What is the significance of Microalbuminuria?

Answer-Microalbuminuria- may be defined as an albumin excretion rate intermediate between normality (2.5-25 mg/day) and macroalbuminuria (250 mg/day). The small increase in urinary albumin excretion is not detected by simple albumin stick tests and requires confirmation by careful quantization in a 24 hr. urine specimen. The importance of micro- albuminuria in the diabetic patient is that it is a signal of early reversible renal damage.

Unlike type 1 diabetes mellitus,in which microalbuminuria is a good indicator of early kidney damage,microalbuminuria is a common finding (even at diagnosis) in type 2 diabetes mellitus and is a risk factor for macrovascular (especially coronary heart) disease. It is a weaker predictor for future kidney disease in type 2 diabetes mellitus.

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