What is C-Peptide Test? (C-Peptide Levels meaning, charts)

C-peptide test is a medical test which helps determines how much insulin the pancreas is producing.
C-peptide test measures insulin-connecting-protein called C-peptide in the blood.

ALL C-Peptide FAQs

Questions and simple answers about c-peptide test requirements and needs as well as the general medical terms related to the C-peptide lab test.

Medical Terms

Insulin C-Peptide, Proinsulin C-Peptide; C-Terminal Insulin, Connecting peptide, and serum C-peptide.

Is C peptide a hormone?

No, C-peptide is a kind of connecting proteins, as c-peptide role is to connect insulin units at the beginning of manufacturing insulin inside pancreas  beta cells.
But, Insulin is a hormone helps the body cells use insulin.
So, what is C-peptide in the blood test? or 

What is the C peptide test?

C-peptide is a pancreatic protein which is found in equal amounts to insulin.
C-peptides are protein fragments derived from endogenous insulin only but not exogenous insulin.
The pancreas produce a chemical called proinsulin which consists of equal amounts of insulin and c-peptide.
Insulin helps the body control the amount of sugar in the blood via linking to glucose units and transport it to the cells.
Don’t miss: Blood Glucose Levels Chart for diagnosis diabetic and non-diabetic

What does C in C-peptide stands for?

The letter “C” stands for “connecting” protein between insulin units, the complete story below.
c-peptide tests and levels chart

Insulin or c-peptide?

For many reasons doctors were preferring to measure the insulin level indirectly through c-peptide test level.
C-peptide and insulin are produced from pancreas at the same rate. so that, C-peptide is a useful marker of insulin production.
But why doctors prefer to test for c-peptide more than insulin itself, more underlying causes:

  1. C-peptide is mainly excreted by the kidney, and its half-life is 3-4 times longer than that of insulin.
  2. 5 to 10 times higher concentration of C‑peptide persist in the peripheral circulation which fluctuate less than insulin.
  3. People with insulin-antibodies can’t test for insulin: because of high prevalence of endogenous anti‑insulin antibodies C‑peptide values reflect the endogenous pancreatic insulin secretion more reliably in insulin‑treated diabetes patients than the measurement of insulin itself.

Why doctor do C-Peptide test?

Testing for C‑peptide is not useful for the routine monitoring of diabetes millitus,
however c-peptide test is a valuable tool when taking therapeutic decisions which are essential for an optimal long‑term metabolic control.
The reasons why to do c-peptide test include:

  1. C-Peptide test formerly used in early stages of type 1 diabetes to check the residual islet cell function.
  2. For newly diagnosed diabetes person: to help determine how much insulin a person’s pancreas is still producing (endogenous insulin).
  3. C-peptide in type 2 diabetes is used to monitor the activity of pancreatic beta cell over time to produce insulin and to determine when is the best time to begin insulin treatment.
  4. For investigation of unexplained hypoglycaemia (had replaced.)
  5. For who has pancreas islet cell transplants, C-peptide levels may be used to verify the effectiveness of treatment and  and for monitoring success after pancreatectomy. (rare).
  6. For whom under risk of metabolic syndrome/insulin resistance, c-peptide test help rule out the causes.
  7. To differentiate between the diagnosis of latent autoimmune diabetes of adults (LADA)and type‑2 diabetes.

How does c-peptide test be done?

C-peptide test can be done from plasma ( a blood sample) or urine sample.

Do I need to fast before a c-peptide blood test?

You have to fast before c-peptide blood test about 12- 16 hours, and the second sample is drawn 2 hours after a meal.
Fasting requires that you to not eat or drink anything but water before the test.
The preparation needed for the insulin C-peptide test includes that you stop biotin consumption for at least 72 hours before the sample collection at the lab.
The complete list: 6 to 12 hr fasting blood test list, fasting before blood test explained

How much c-peptide test cost?

The price may reach $69.00 in US or around £160 in UK.

When is the time to receive the C-peptide results?

Wait time: about 1-2 days if you have the test in some laboratories , while advanced labs may consume one hour to finish c-peptide testing procedures.
However, the c-peptide test time is about 15 to 60 minutes.
Complete guide: How long does it take to receive a blood test results? Waiting time explained

C-Peptide Levels Chart

C-Peptide Reference Range

Fasting: 0.9 – 7.1 ng/mL
Non fasting c peptide range
PP: 2.73 – 5.64 ng/ml
In urine: 2.5 – 249 μg/day

C-peptide normal range Pmol/L Chart

The next table conclude the conversions of serum C-peptide normal ranges into many different measuring units.
The laboratory units used below: pmol/L, nmol/L, ng/mL, ng/dL, ng/100mL, ng%, ng/L, µg/L

Unit Fasting lower value Fasting higher value Post-prandial lower limit Post-prandial higher limit
ng/mL 0.9 7.1 2.73 5.64
ng/dL 90 710 273 564
ng/100mL 90 710 273 564
ng% 90 710 273 564
ng/L 900 7100 2730 5640
µg/L 0.9 7.1 2.73 5.64
nmol/L 0.298 2.3508 0.9039 1.8674
pmol/L 297.9846 2350.7676 903.8867 1867.3704

* We recommend using SI units when reporting clinical laboratory results.
μg stands for micro-gram (ug).
ng stands for nano-gram.
Do you know: What does reference range means?

What do C-Peptide blood test results mean?

C peptide results interpretation depending on the medical conditions.
Also see another article about how to deal with 10 Tips For Abnormal Blood Test Results

What is a normal C peptide test result?

The normal C-peptide result is any value lies between the normal limits in the table above.
When c-peptide reading is within the expected healthy ranges it’s said that the pancreas is working well to produce sufficient insulin for body energy.
Normal c-peptide tells that you have normal insulin levels and you will not develop insulin-dependent diabetes.
Blood test results with normal c-peptide may or may not show normal glucose level, that’s because the glucose may be high due to another causes other insulin insufficiency.

What does it means when C-peptide test results high?

High c-peptide will cause high insulin levels and low glucose (hypoglycemia) until the pancreas beta cells destroy themselves.
then glucose will be elevated again because there’s no insulin again from dead pancreas.
Elevated C‑peptide levels is a result of increased β‑cell activity such as in hyperinsulinism, renal insufficiency, and obesity.
Blood test results may show high C‑peptide levels and increasing hyperlipoproteinaemia and hypertension too.
An elevated c-peptide level may be due to one or more of the following:
What causes high C peptide levels are:

  • Insulinoma: a tumor (noncancerous growth) of pancreas cells which produce more insulin and c-peptide over the normal levels.
  • Uncontrolled type 2 diabetes: to overstimulate body cells to use glucose.
  • High insulin dose will not cause high c-peptide level because the c-peptide only found with endogenous insulin.

What do low c-peptide levels mean?

What does it mean when insulin levels are low?
If a person’s body makes too little insulin or the cells become resistant to its effects, cells starve.
Low c-peptide means low insulin level which in turn means insufficient glucose transported to the body cells while the blood stream is full with unused glucose.
Low C-peptide comes from inflammation of the pancreas or necrosis (death of pancreatic cells),
also the removal of pancreas is the obvious cause of low c peptide levels in the blood.
Excess glucose resulted in the blood may cause inflammation to the kidney and may be increase triglycerides level the main reasons behind coronary heart diseases.
The causes of low c-peptide:

  1. Starvation.
  2. Factitious hypoglycemia.
  3. Hypoinsulinism (NIDDM, IDDM).
  4. Addison’s disease.
  5. After radical pancreatectomy.

Low c peptide normal glucose meaning

Low c-peptide is a result of low insulin production after beta cells inflammation,
people with balanced diet and high carbs. may still show normal blood glucose even after c-peptide and insulin levels decreased.

The meaning of “High c peptide normal glucose”

Normal glucose mean your body still be able to produce enough insulin to control the glucose in the blood, but what if the c-peptide is high, does it mean high insulin too?
C-peptide and insulin are two faces from the same coin, they come high or low at the same time.
If the diagnosis is type 2 DM at the beginning then your c-peptide and insulin should become higher over the time to overstimulate cells to absorb more sugar.
But, over the time and with poor diabetes management the hyper secretions from pancreas will cause damage to the pancreas cells and lead to no insulin nor c-peptide production, and the sugar back to the elevated levels.

The meaning of “high insulin normal c-peptide and glucose levels”

If you’re taking insulin injections (exogenous insulin) your insulin level may be in the target values or be higher a bit,
while the c-peptide is not found in the exogenous insulin preparations it will remain on the normal.
insulin cpeptide and obesity

How to increase c-peptide levels naturally?

For persons with low c-peptide,

Can c peptide increased?

You should know that the goal from c-peptide test is for indirect measurement of insulin levels thus we should seek for increasing insulin when c-peptide is low.
However, the beta cells in T1 will still adjust the amount of insulin/c-peptide production upon the amount of elevated glucose.
Some recent studies suggest that the s-peptide is an active protein and has a biological role in diabetes management.
There is evidence that C‑peptide replacement accompanied with administering insulin, may prevent the development or retard the progression of long-term complications in type 1 diabetes mellitus.

Natural Methods to increase c-peptide

Guide for how to increase c-peptide levels and treat hypoglycemia that may come from
excessive supplementation of insulin, alcohol consumption, inherited liver enzyme deficiencies, liver or kidney disease, or by insulinomas.

  • Stop alcohol consumption to prevent more damage to the beta cells.
  • Follow-up insulin dosage with your doctor to ensure there is no excessive insulin in the blood.
  • Take blood test for liver function test to make sure you don’t have any genetic diseases.
  • Do kidney function test to exclude any renal injury. The concentration of c peptide in urine is about 20‑50 fold higher than in serum. C‑peptide levels are therefore elevated in renal disease.

Keeping glucose levels stable will also regulate insulin levels and stop c-peptide secretions.

  1. Avoid added sugars.
  2. Eat a diet high in fiber.
  3. Maintain a healthy weight.
  4. Exercise regularly.

How to lower c-peptide levels?

Many patients ask me what if my c peptide is high and what to do if my c-peptide test results came high
Ask your doctor about some drugs act against pancreas cancerous cells to stop spreading.
Eating an insulin resistance diet may help reduce high cpeptide and insulin levels:

  1. Limit Carbohydrates.
  2. Avoid Sweetened Beverages.
  3. Eat More Fiber.
  4. Eat Healthy Fats.
  5. Get Enough Protein.
  6. Eat Dairy.
  7. Think About Your Portions.

C-peptide test in urine

c-peptide in urine sample

Who does need urinary c-peptide test?

People need continuous assessment of β‑cell function, also may test c-peptide in urine rather than in blood, also it’s useful in the conditions below:

  1. To assess pancreatic function in gestational diabetes.
  2. For patients with unstable glycemic control in insulin‑dependent diabetes mellitus (IDDM)
  3. For children: as kids need to a lot of blood samples which is not practical in children.

Useful to see: Urine Sugar Levels Chart, What Does Sugar in Urine Mean?

  • Doctor request C‑peptide, insulin and glucose for differential diagnosis of hypoglycemia (factitious hypoglycemia and hypoglycemia caused by hyperinsulinism), however it’s help toning an appropriate management and therapy of the patients.
  • High insulin and normal/high c-peptide levels means type 2 dm and high glucose.
  • Low c-peptide with high glucose means damaged beta cells and type 1 DM.
  • High insulin and high c-peptide and low glucose”hypoglycemia” indicate insulinoma.
  • MODY diabetes is a rare form of diabetes which is different from both Type 1 and Type 2 diabetes, and runs strongly in families with 50% chance of inheriting it from them.

References for Diabetes patients:

More to come:

  • Insulin levels
  • Metabolic syndrome
  • Insulin resistance
  • GAD test
  • hypoinsulinism
  • hyperinsulinism
  • Insulinoma and Diabetes.
  • GAD65 antibody test
  • Proinsulin level.

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Dr.Megan Ralf

A Medical laboratory Scientist who devoted his life to medical and laboratory sciences, writes his everyday expertise dealing with various pathological conditions through laboratory diagnosis of different body fluids, also participating in many workshops for first aids, infection control, and urgent care. Also Dr Megan Ralf coaching many medical teams.

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