Insulin level 

What sample is needed for Insulin level?

1. This test is done on the serum of the patient.
2. A fasting sample is preferred.
   1. Freeze the sample.
3. With OGTT, draw a fasting sample at 30, 60. and 120 minutes.
4. Avoid hemolysis.

What are the Indications for Insulin level?

1. It helps in the management of glucose metabolism.
2. Insulin level helps in the diagnosis of insulinoma.
3. Insulin levels can be advised in starting the initial therapy for patients with type 2 Diabetes Mellitus.
   1. In the case of lower insulin levels, insulin or an insulin secretagogue is the most adequate treatment.
4. Insulin level is advised in case of fasting hypoglycemia.
   1. It helps patients with diabetes requiring insulin as treatment and patients who can control it with diet only.
5. Advised in the case of abnormal carbohydrate and lipid metabolism.
6. Insulin was recently advised in case of polycystic ovary syndrome.
   1. Ladies with this disease have insulin resistance and abnormal carbohydrate metabolism that may respond to oral hypoglycemic agents.
7. Insulin is not clinically advised for the diagnosis of diabetes mellitus.
   1. People were estimating insulin levels in OGTT to help early diagnose diabetes mellitus.

What are the precautions for insulin levels?

1. Keep in mind that insulin antibodies can interfere with radioimmunoassay.
2. The patients treated with insulin develop antibodies.
3. Obesity and food may increase insulin levels.
4. Radioisotopes, if given before the test, will affect the result.
5. Drugs like corticosteroids, oral contraceptives, and levodopa increase insulin levels.

How will you define Insulin level?

1. Total insulin measures free and bound insulin.
2. Insulin keeps glucose levels under control.
3. It is an islet cell, an anabolic hormone that controls glucose uptake, fat, and protein synthesis.
4. It is a protein hormone produced by the beta cells of islets of Langerhans in the pancreas.
5. Its molecular weight is 6000 D and consists of 51 amino acids.
6. It has two amino acid chains, A and B, joined by the disulfide bridge.
7. Insulin in humans is similar to insulin in animals.
8. Now, most patients are treated with human recombinant insulin.

What is the mechanism for Insulin formation?

1. Insulin forms from inactive preproinsulin, consisting of 100 amino acids. It is not found in the blood.
2. Preproinsulin converts into proinsulin (big insulin) which cleaves by the proteolytic enzymes.
   1. Proinsulin consists of alpha and beta chains connected by an area called a connecting peptide (C-peptide).
3. There is the formation of insulin and C-peptide.
   1. C-peptide has no insulin-like action but can be measured to assess the β-cell function.
4. Insulin is stored in secretory granules, and when plasma glucose is increased, insulin is released by exostosis.
5. Insulin half-life is 10 to 25 minutes (another reference is 4 to 9 minutes).

How Insulin will regulate carbohydrate metabolism?

1. Insulin maintains blood glucose at a constant level within the defined normal range.
2. Insulin facilitates the movement of glucose from the bloodstream into the cell.
3. Insulin is the anabolic hormone that stimulates glucose uptake into the fat and muscles.
4. Insulin promotes the conversion of glucose into glycogen or fat storage.
5. Insulin inhibits glucose production from the liver.
6. Insulin stimulates protein synthesis and inhibits protein breakdown.

7. The insulin level secretion is dependent upon the level of glucose.

What is the effect of starvation and fasting on Insulin secretion?

1. Glucose decreases in the first three days of the fast at around 18 mg/dL.
2. Glucagon secretion is doubled to maintain the glucose level.
3. Lipolysis and liver ketogenesis are stimulated.
4. Ketone bodies, fatty acids, and glycerol levels in the blood are increased.
5. Initially, triglyceride increases and later decreases.
6. Cholesterol also decreases.
7. Due to catabolism in starvation, the concentration of the protein in the blood increases.
8. There are chances to develop metabolic acidosis.
   1. Reduced blood pH.
   2. Reduced pCO2.

What is the effect of OGTT and fasting glucose on insulin?

1. There are suggestions that insulin level on the same sample with OGTT level is more reliable than a single insulin level.
2. Patient with Juvenile diabetes has a typical picture in OGTT:
   1. Low fasting insulin level and display flat GT insulin curve.
   2. This shows that there is no increase in the insulin level.

3. Patients with mild diabetes mellitus show:
   1. Normal fasting insulin level.
   2. GT curve with a delayed rise in insulin.
4. Patients with diabetes mellitus type 2 show:
   1. Fasting insulin level is normal, but the insulin’s response to glucose is delayed.

5. Insulinoma has a characteristic picture of the fasting glucose level and insulin level.
   1. There is increased insulin with low fasting glucose.
   2. Persistent hypoglycemia with an increased insulin level.
   3. The insulin/glucose ratio should be less than 0.3.
   4. The insulin/fasting glucose ratio in Insulinoma is more than 0.3.

How will you calculate insulin level using Turner’s amended formula? 

1. When the glucose level increases, the insulin level also increases. When the glucose level decreases then, insulin secretion stops.
2. Insulin levels will be low in Insulin-dependent diabetes mellitus.
3. While insulin levels are high in non-insulin-dependent diabetes mellitus due to insulin resistance, the patient needs more insulin.

Insulinoma:

How will you give important facts about Insulinoma?

1. This is the tumor of beta cells in the islets cells of  Langerhans of the pancreas.
2. There is persistent hypoglycemia, which may be below 30 mg/dL.
3. There is a raised level of insulin.
4. There is a persistently high level of C-peptide.
5. The Turner (modified)  insulin/glucose ratio is above 50.

Insulinoma

What is important about insulinoma?

1. Insulinomas are the tumors of Beta-cells insulin-producing pancreatic islet cell tumors.
2. About 80% of these tumors are single adenomas, about 10% are multiple, and about 10% are carcinomas.
3. Insulinomas are typically associated with hypoglycemia.

How to diagnose Insulinoma?

1. Diagnosis of islet cell tumors is important.
2. Whipple’s triad for the diagnosis of insulinoma:
   1. Symptoms are compatible with hypoglycemia while fasting.
   2. A fasting blood glucose level is important while the patient is having symptoms. This may be as low as 10 mg/dL (0.55 mmol/L).
   3. The patient’s symptoms improve when he/she is given glucose.
3. It is required to find the insulin level which is elevated.
4. Plasma or serum insulin/glucose ratio.
   1. In the active insulinoma, insulin level will be elevated.
5. Amended ratio of insulin/glucose ratio.
   1. Serum insulin level x 100 / Serum glucose – 30 mg/dL.
   2. Such a ratio of >50 is suggestive of Insulinoma.
6. Tolbutamide test.
   1. A special water-soluble form of tolbutamide is given intravenously.
   2. In a normal person, there is a rapid fall in the glucose level in 30 to 40 minutes, followed by a return to normal level in 1.5 to 3 hours.
   3. In patients with insulinoma, glucose levels rapidly fall compared to the normal person (40% to 65% of the baseline).

What is the Normal insulin level?

Source 1

Insulin free

• Infants and  prepubertal child = <13 µU/mL
• Prepubertal child and adult = <17 µU/mL
  • To convert into SI units x 6.945 = pmol/L
• Insulin immunoreactive 
  • 2 to 12 year = <10 µU/mL
  • Adult = <35 µU/mL
• Insulin with oral glucose tolerance test
  • 0 minute = 3 to 28 µU/mL
  • 30 minutes = 20 to 112 µU/mL
  • 60 minutes = 29 to 88 µU/mL
  • 120 minutes = 22 to 79 µU/mL
  • 180 minutes = 4 to 62 µU/mL

Source 2

• Adult = 6 to 26  µU/mL (43 to 186 pmol/L)
• Newborn = 3 to 20 µU /mL
  • Possible critical value = >30 µU/mL

What are the conditions where there is an Increased Insulin level?

1. Insulinoma.
   1. Fasting insulin level is >50 µU/mL in the presence of normal or low blood glucose.
2. Insulin autoimmune syndrome.
3. Acromegaly.
   1. There are raised glucose levels.
   2. The overproduction of growth hormone in these patients gives rise to constant stimuli for insulin production.
4. Cushing’s syndrome.
   1. There is a raised level of glucose due to the overproduction of cortisol.
   2. There is constant stimulation for the production of insulin.
5. Pancreatic islet cell hyperplasia.
6. Obesity. There is a constantly raised level of insulin.
7. Fructose or galactose intolerance.
8. Cirrhosis occurs when there is insufficient clearance from the blood circulation.

What are the conditions where insulin level is decreased or absent?

1. Diabetes mellitus type 1 (maybe a total lack or very low).
2. In diabetes mellitus type 2, there is a low insulin resistance level.
3. In the case of severe diabetes mellitus with ketosis and weight loss.
4. In less severe cases of diabetes, insulin is present but at a lower glucose level.
5. Hypopituitarism.

• Critical Value of Insulin = >30 mU/mL

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