The C-Peptide Test: How Doctors Measure Your Own Insulin Production

The lab portal pings at 9:40 on a Tuesday. You scroll past cholesterol and glucose, and there it is — a line you’ve never seen before: C-peptide, 1.4 ng/mL. No flag, no explanation, and a search engine full of contradictory answers. If that scenario sounds familiar, you’re in good company. C-peptide is one of the most quietly useful numbers in diabetes care, and one of the least explained.

Here’s the odd part: the molecule itself doesn’t do much. C-peptide is essentially a leftover — a fragment snipped off when your pancreas assembles insulin. Yet that leftover tells doctors something insulin itself can’t reliably reveal: how hard your own beta cells are actually working.

That single distinction is why this test can help separate type 1 diabetes from type 2, unmask a rare insulin-producing tumor, or explain a mystery episode of low blood sugar. Let’s walk through what the number means, honestly, without the myths.

What Is C-Peptide, Exactly?

Deep in your pancreas, beta cells build insulin the way a factory builds furniture — from a larger precursor. That precursor is called proinsulin, and it folds into shape with a connecting strand holding two ends together. When the beta cell is ready to release insulin, an enzyme snips out that connecting strand. The strand is C-peptide; the “C” stands for “connecting.”

The crucial detail is the arithmetic. Every time one molecule of insulin leaves the pancreas, one molecule of C-peptide leaves with it — a strict 1:1 ratio. So while C-peptide has little known biological work of its own, its concentration in your blood is a faithful receipt for insulin production. High C-peptide means the pancreas is releasing a lot of insulin. Low C-peptide means it’s releasing very little.

Why not just measure insulin directly? Two practical problems get in the way. First, roughly half of the insulin your pancreas releases is pulled out of circulation by the liver on its first pass, before it ever reaches the vein in your arm. C-peptide skips that filter almost entirely. Second, insulin vanishes fast — its half-life in blood is only a few minutes, while C-peptide lingers for about 30 minutes, giving labs a steadier, more measurable signal.

Think of it this way: insulin is the busy employee who’s hard to catch at their desk. C-peptide is the timestamped badge swipe proving they showed up.

Why Would a Doctor Order a C-Peptide Test?

Blood glucose and HbA1c tell doctors how much sugar is in your blood. Neither one explains why. C-peptide fills that gap by answering a different question: is the pancreas underproducing insulin, producing plenty that the body ignores, or producing far too much?

In practice, clinicians reach for the test in a handful of situations:

• Sorting out diabetes type. When it’s unclear whether someone has type 1 diabetes (an autoimmune loss of beta cells) or type 2 (insulin resistance with relatively preserved production), C-peptide can tip the balance. This matters most in adults diagnosed at an age where either type is plausible.
• Investigating low blood sugar. In someone with unexplained hypoglycemia, a high C-peptide during the episode points toward the body’s own overproduction — for example, a rare insulin-secreting tumor called an insulinoma — while a low C-peptide alongside high insulin suggests the insulin came from an injection.
• Tracking remaining beta-cell function. In established type 1 diabetes, C-peptide shows how much natural production survives, which is also central to research on preserving beta cells.
• Evaluating pancreas health after pancreatic surgery, or as part of assessing insulin resistance.

One thing the test is not for: routine screening in healthy people. If your annual bloodwork doesn’t include it, that’s not an oversight — it’s appropriate. The number is most meaningful when there’s a specific clinical question, and always alongside a glucose measured at the same moment.

What Does the C-Peptide Test Involve?

For most people, it’s an ordinary blood draw — a needle in an arm vein, a single tube, done in under five minutes. The variations are worth knowing, because they change what your result means.

Fasting blood test. The most common version. You typically go without food for 8 to 12 hours beforehand, so the result reflects your baseline insulin output rather than the surge that follows a meal. Water is generally fine; your care team will confirm specifics.

Random or paired test. Sometimes C-peptide is drawn without fasting, especially during a suspected low-blood-sugar episode. Here, timing is everything: the value is interpreted against the glucose level measured from the same draw. A C-peptide that would be unremarkable at a normal glucose becomes very telling when glucose is low.

Stimulated test. To see how the pancreas responds under demand, doctors may measure C-peptide after a standardized liquid meal or an injection that provokes insulin release. This shows reserve capacity, not just idle output — useful when distinguishing early type 1 diabetes from other forms.

Urine test. C-peptide can also be measured in urine, sometimes over 24 hours or as a spot sample compared with creatinine. It’s less precise but painless and practical, particularly for children.

Risks mirror any blood draw: brief sting, possible small bruise, rarely lightheadedness. Results usually return within a few days, reported in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L), depending on the lab.

How Should You Prepare for the Test?

Preparation is simple, but the details genuinely change your number, so they’re worth taking seriously.

If your doctor ordered a fasting test, treat the fast as part of the test itself. Eating even a small snack triggers insulin release, and C-peptide will rise right along with it — a result that could make normal production look excessive. Most labs ask for 8 to 12 hours without food or caloric drinks. Plain water is usually encouraged; it keeps veins easier to find.

Tell your care team about every medicine and supplement you take, because several can move the result. Certain diabetes medicines work precisely by prodding the pancreas to release more insulin, which raises C-peptide. Injected insulin does the opposite in an indirect way: it contains no C-peptide, and by lowering glucose it can quiet your own beta cells. Never stop or adjust any medication on your own — whether to pause anything before the draw is a decision for the prescriber, not the lab slip.

A few smaller points people rarely hear:

• Schedule morning draws when possible; fasting overnight is easier than fasting through a workday.
• Recent illness or significant stress can shift glucose and insulin dynamics, so mention if you’ve been sick.
• If the test is paired with a glucose measurement — and it usually should be — both come from the same draw, so no extra needle is needed.

None of this requires heroics. It mostly requires an empty stomach and an honest medication list.

What Is a Normal C-Peptide Level?

Here’s where honesty matters more than a tidy number: there is no single universal “normal.” Reference ranges differ between laboratories because assays differ, and units differ too — some labs report ng/mL, others nmol/L or pmol/L. Always read your result against the range printed on your report.

That said, typical fasting values cluster in a recognizable band, and research studies have converged on some useful interpretive thresholds:

Measurement	Commonly cited values	What it generally suggests
Fasting C-peptide (typical lab range)	~0.5–2.0 ng/mL (~0.17–0.83 nmol/L)	Baseline insulin production within expected limits
Very low stimulated C-peptide	<0.2 nmol/L (<0.6 ng/mL)	Consistent with type 1 diabetes; substantial insulin deficiency
Preserved stimulated C-peptide	>0.6 nmol/L (>1.8 ng/mL)	More consistent with type 2 diabetes or other insulin-resistant states
Elevated fasting C-peptide	Above the lab’s upper limit	Possible insulin resistance, kidney impairment, or rarely an insulinoma

Two caveats deserve emphasis. First, these thresholds come from studies of people with diabetes and are guides, not verdicts — the gray zone between 0.2 and 0.6 nmol/L requires clinical judgment. Second, a C-peptide value floating alone tells you surprisingly little. The same number can be reassuring at a normal glucose and alarming at a low one. Interpretation is a paired exercise, which is exactly why this test belongs in a doctor’s hands rather than a search bar.

What Level of C-Peptide Indicates Type 1 Diabetes?

This is the question people search most, so let’s answer it plainly and then add the necessary honesty.

In established type 1 diabetes, C-peptide is low — often very low. Research groups commonly use a stimulated C-peptide below 0.2 nmol/L (roughly 0.6 ng/mL) as a marker of the severe insulin deficiency that defines the condition, and many people with long-standing type 1 fall below 0.08 nmol/L. The logic is straightforward: type 1 is an autoimmune process that destroys beta cells, and fewer beta cells means less insulin and, in lockstep, less C-peptide.

Now the honesty. Timing changes everything. In the first months after diagnosis, many people with type 1 still make meaningful insulin — the so-called honeymoon phase — so an early C-peptide can sit in the ambiguous middle range. A single borderline value near diagnosis neither confirms nor excludes type 1. That’s why clinicians often pair C-peptide with autoantibody tests, which detect the immune attack itself, and sometimes simply retest a year or more later, when the distinction becomes much clearer.

The reverse error matters too. A preserved C-peptide years after diagnosis — say, above 0.6 nmol/L — makes classic type 1 unlikely and prompts doctors to reconsider: could this be type 2, or one of the inherited forms known as MODY?

So the honest summary: a very low C-peptide strongly supports type 1 diabetes, especially years after diagnosis, but no single cutoff diagnoses it alone. Context, antibodies, and time complete the picture.

What Conditions Cause High C-Peptide?

A high C-peptide means your pancreas is releasing more insulin than typical. The important question is why, and the answers range from extremely common to genuinely rare.

• Insulin resistance — by far the most common cause. When muscle, liver, and fat cells respond sluggishly to insulin, the pancreas compensates by making more. C-peptide rises as a marker of that extra effort. Insulin resistance travels with prediabetes, early type 2 diabetes, excess abdominal fat, and metabolic syndrome, and it affects a large share of adults; the CDC estimates about 98 million American adults have prediabetes.
• Type 2 diabetes, especially early on. In its first years, type 2 diabetes often features high or normal C-peptide — the pancreas working overtime against resistance. Production tends to decline gradually over years.
• Chronic kidney disease. Here’s a trap worth knowing: the kidneys clear C-peptide from the blood. When kidney function falls, C-peptide accumulates and reads high even if production hasn’t changed. Doctors interpret results cautiously in anyone with reduced kidney function.
• Insulinoma. A rare tumor of the beta cells that secretes insulin autonomously, causing high C-peptide together with episodes of low blood sugar. Rare means rare — these tumors occur in only a few people per million per year.
• Certain medicines that stimulate the pancreas to release insulin will raise C-peptide as an expected effect, not a malfunction.
• Cushing’s syndrome and pregnancy-related hormonal shifts can also increase insulin demand and, with it, C-peptide.

For most people, a high result is a metabolic signal — a nudge about insulin resistance — not a hidden tumor.

What Causes Low C-Peptide?

Low C-peptide means the pancreas is releasing little insulin. Sometimes that’s a problem; sometimes it’s simply physiology doing its job. Sorting the two depends on what your glucose was doing at the same moment.

When low C-peptide reflects lost production:

• Type 1 diabetes. The classic cause. Autoimmune destruction of beta cells drives C-peptide down, often to barely detectable levels over time.
• Long-standing type 2 diabetes. After years of heavy demand, beta cells can fatigue and fail; C-peptide that was once high drifts low. This shift sometimes explains why treatments that worked for a decade stop working.
• Pancreatic disease or surgery. Chronic pancreatitis, cystic fibrosis–related damage, or removal of part of the pancreas all reduce the beta-cell workforce.

When low C-peptide is expected, not alarming:

• Fasting in a healthy person. With no food arriving, insulin output idles low. A modest fasting value in someone with normal glucose is unremarkable.
• Insulin therapy. Injected insulin contains no C-peptide, and by keeping glucose controlled it lets the person’s own beta cells rest — so measured C-peptide falls. This isn’t damage; it’s suppression.

There’s one scenario where low C-peptide is diagnostic gold: hypoglycemia with high insulin but low C-peptide. That mismatch tells doctors the circulating insulin didn’t come from the pancreas — it was injected. This pattern helps identify accidental dosing errors and, rarely, deliberate misuse.

The pattern to remember: low C-peptide plus high glucose signals a struggling pancreas. Low C-peptide plus normal glucose is often just a quiet morning.

Is C-Peptide the Same as HbA1c?

No — and confusing them is understandable, because both appear on diabetes-related lab reports. They measure entirely different things, on entirely different timescales.

HbA1c is a rearview mirror for sugar. It measures the percentage of hemoglobin in your red blood cells that has glucose stuck to it. Because red cells live about three months, HbA1c summarizes your average blood glucose over roughly the past 8 to 12 weeks. It answers: how well controlled has my blood sugar been?

C-peptide is a snapshot of the factory. It reflects how much insulin your pancreas was releasing at the moment of the blood draw. It answers: how much insulin am I making myself?

The two can move in any combination, and the combinations are informative. Someone with early type 2 diabetes might show a high HbA1c and a high C-peptide — plenty of insulin, but the body resists it. Someone with new type 1 might show the same high HbA1c with a low C-peptide — the sugar is high because production has collapsed. Two identical HbA1c results, two opposite mechanisms, two different care paths.

A practical consequence: improving your HbA1c doesn’t directly “fix” your C-peptide, and a normal HbA1c doesn’t guarantee normal insulin production. In insulin resistance, C-peptide can run high for years while HbA1c stays in range — the pancreas compensating silently. That’s one reason doctors occasionally check both: the mirror tells you where you’ve been, the snapshot hints at where you’re headed.

How C-Peptide Helps Sort Out Confusing Diabetes Diagnoses

Textbooks make diabetes classification sound clean: type 1 in lean children, type 2 in adults with metabolic risk factors. Real clinics are messier. Roughly a third of type 1 diabetes is diagnosed in adulthood, type 2 increasingly appears in teenagers, and studies suggest a meaningful minority of people carry a label that doesn’t quite fit. Misclassification isn’t academic — it shapes which treatments are offered and how urgently.

C-peptide earns its keep in three gray zones:

• Adults diagnosed between roughly 30 and 50. An adult with new diabetes and no obvious insulin resistance could have slowly evolving autoimmune diabetes — sometimes called LADA (latent autoimmune diabetes in adults) — which begins looking like type 2 but progresses toward insulin deficiency. Falling C-peptide over serial tests, plus positive autoantibodies, reveals the true trajectory.
• Suspected MODY. Maturity-onset diabetes of the young is a family of inherited, single-gene forms of diabetes, often misdiagnosed as type 1. A person labeled type 1 for years who still shows robust C-peptide is a candidate for genetic testing — and in some MODY subtypes, confirming the diagnosis changes management substantially.
• Long-standing diabetes with treatment questions. When someone with presumed type 2 stops responding to pancreas-stimulating medicines, a low C-peptide can explain why: there’s little left to stimulate.

British researchers Jones and Hattersley, whose 2013 review remains a touchstone, put it memorably: C-peptide testing is most useful not at diagnosis, when results overlap, but three to five years in — when the types have separated and the number speaks clearly.

C-Peptide and the Mystery of Low Blood Sugar

Hypoglycemia in someone without diabetes is a genuine medical puzzle, and C-peptide is one of the sharpest tools for solving it. The test works like a forensic question: when your glucose dropped, where did the insulin come from?

Doctors ideally draw blood during an episode — sometimes provoked under supervision with a monitored fast of up to 72 hours — and measure glucose, insulin, and C-peptide from the same tube. The combinations tell distinct stories:

• Low glucose + high insulin + high C-peptide: the body is overproducing its own insulin. The leading suspects are an insulinoma (rare, and usually benign) or certain medicines that stimulate insulin release.
• Low glucose + high insulin + low C-peptide: the insulin came from outside the body. Injected insulin carries no C-peptide, so the mismatch is unmistakable. This pattern identifies dosing accidents and, occasionally, covert misuse.
• Low glucose + low insulin + low C-peptide: insulin isn’t the culprit at all. Attention turns to other causes — hormone deficiencies, liver disease, alcohol effects, or critical illness.

Timing is the entire game here. A C-peptide drawn hours after an episode, once glucose has recovered, may look perfectly normal and prove nothing. If you’ve had unexplained episodes of shakiness, sweating, confusion, or fainting that improve with food, keep a written log of when they happen — it helps your doctor decide whether and how to capture the moment on paper.

One reassurance is worth stating: most hypoglycemia workups do not end in a tumor diagnosis. Insulinomas affect only a few people per million each year.

How Do You Lower a High C-Peptide?

People search “how to fix high C-peptide,” and the honest answer starts with a reframe: C-peptide isn’t the problem to fix. It’s a gauge. When it runs high because of insulin resistance — the usual reason — the meaningful goal is improving how your body responds to insulin. Do that, and the pancreas can ease off; C-peptide tends to follow.

The evidence for what improves insulin sensitivity is unusually strong:

• Physical activity, especially the consistent kind. Muscle is the body’s biggest glucose consumer, and exercise lets muscles take up glucose with less insulin — an effect that begins with a single session and compounds with regular training. Mainstream guidelines suggest at least 150 minutes of moderate activity weekly, plus strength work twice a week.
• Modest weight loss, if weight is a factor. In the landmark Diabetes Prevention Program, losing 5–7% of body weight combined with activity cut the risk of progressing from prediabetes to type 2 diabetes by 58%. That’s not a slogan; it’s one of the best-replicated findings in preventive medicine.
• Sleep and eating patterns. Short sleep measurably worsens insulin sensitivity within days, and dietary patterns built on vegetables, whole grains, legumes, and unsaturated fats consistently associate with better metabolic markers than refined-carbohydrate-heavy diets.

Two cautions. If your C-peptide is elevated because of reduced kidney function, lifestyle changes won’t move it — the number reflects clearance, not production. And if it’s elevated with episodes of low blood sugar, that needs medical evaluation, not a fitness plan. Bring the result to your doctor before building a strategy around it.

What Can Throw Off C-Peptide Results?

Every lab test has failure modes, and knowing C-peptide’s keeps you from over-reading a single number.

• Kidney function is the big one. The kidneys clear C-peptide; insulin, by contrast, is largely cleared by the liver. In chronic kidney disease, C-peptide lingers and reads artificially high — a value that says more about filtration than about the pancreas.
• Food and fasting status. A “fasting” test after a granola bar isn’t a fasting test. Post-meal C-peptide can be several times the fasting level in a healthy person.
• Current glucose level. Beta cells respond to glucose in real time. If your blood sugar happens to be low at the draw, C-peptide will be suppressed — which is why very low values are hard to interpret without a paired glucose. High glucose stimulates release, within the limits of what the pancreas can do.
• Medications. Insulin therapy suppresses your own production; pancreas-stimulating diabetes medicines boost it. Both effects are expected, but both muddy interpretation if the lab doesn’t know about them.
• Assay and unit differences. A result of 1.5 could be ng/mL at one lab and nearly meaningless compared against another lab’s nmol/L range. Converting between the two involves a factor of roughly 0.33 — one more reason to compare results only within the same laboratory when tracking trends.
• Sample handling. C-peptide is reasonably stable, but delays in processing can degrade it slightly, nudging results downward.

The practical takeaway: repeat testing at the same lab, under the same conditions, tells a far truer story than any single value.

When Should You See a Doctor?

A lab number rarely demands urgency by itself, but the symptoms surrounding it sometimes do. Here’s a sensible triage.

Seek care promptly — same day or emergency services — if you experience:

• Confusion, slurred speech, seizure, or loss of consciousness, especially if it improves after eating or drinking something sugary. Severe hypoglycemia is a medical emergency.
• Rapid onset of extreme thirst, frequent urination, unexplained weight loss, deep or rapid breathing, fruity-smelling breath, nausea, or abdominal pain. Together these can signal diabetic ketoacidosis, a dangerous complication of untreated insulin deficiency that can develop over days.

Make a routine appointment if:

• You’ve noticed persistent thirst, increased urination, blurry vision, slow-healing cuts, or fatigue — the quieter signature of high blood sugar.
• You have recurring episodes of shakiness, sweating, hunger, or lightheadedness relieved by food, particularly if you don’t have diabetes.
• You have diabetes and your usual treatment seems to be losing effectiveness, or you were diagnosed as an adult and have always wondered whether your type is correct.
• A C-peptide result on your portal is flagged high or low and no one has walked you through it.

And bring context to the visit. Note when symptoms occur relative to meals, any family history of diabetes diagnosed young, and a complete list of medicines and supplements. C-peptide is an interpretive test — the more context your clinician has, the more the number can actually say.

Reading Your Own Report: A Realistic Bottom Line

Strip away the biochemistry and the c peptide test answers one elegant question: how much insulin is your pancreas making right now? That framing keeps the result in proportion.

A value inside your lab’s reference range, drawn fasting, with a normal glucose beside it, is exactly what it looks like — unremarkable. A high value most often points toward insulin resistance, which is common, consequential, and meaningfully responsive to activity, sleep, and modest weight change. A low value matters most in context: alarming alongside high glucose, expected alongside an overnight fast or insulin therapy.

If there’s one opinion this article will stand behind, it’s this: the single most underused feature of C-peptide is the trend. One measurement is a photograph; two or three over months or years are a film. A C-peptide that holds steady in someone with type 2 diabetes tells a different story than one sliding downward, and a robust value five years after a type 1 diagnosis is a legitimate reason to revisit the diagnosis itself. Serial testing at the same laboratory, interpreted by someone who knows your history, extracts far more truth from this test than any threshold pulled from a search result.

The number on your portal isn’t a verdict. It’s a receipt from your pancreas — and receipts are only meaningful to someone who knows what was ordered. That someone is your doctor, with you across the desk asking good questions. Now you have them ready.

Frequently asked questions

What level of C-peptide indicates type 1 diabetes?

In established type 1 diabetes, stimulated C-peptide is typically below 0.2 nmol/L (about 0.6 ng/mL), reflecting severe loss of insulin production. However, no single cutoff diagnoses type 1 on its own. Early after diagnosis, many people still make meaningful insulin, so values can fall in a gray zone. Doctors combine C-peptide with autoantibody tests, glucose levels, and clinical history — and sometimes retest years later, when the distinction becomes clearer.

Is C-peptide the same as HbA1c?

No. HbA1c measures how much glucose has attached to your red blood cells, summarizing average blood sugar over roughly the past three months. C-peptide measures how much insulin your pancreas was producing at the moment of the blood draw. Two people with identical HbA1c results can have opposite C-peptide values — one overproducing insulin against resistance, the other barely producing any — which points to different types of diabetes and different care.

How do you fix a high C-peptide?

You address the cause rather than the number. Most high C-peptide reflects insulin resistance, which improves with regular physical activity, modest weight loss when relevant, better sleep, and a diet lower in refined carbohydrates. In the Diabetes Prevention Program, losing 5–7% of body weight with activity cut diabetes risk by 58%. If the elevation stems from kidney disease or comes with low blood sugar episodes, it needs medical evaluation, not lifestyle changes alone.

What conditions cause high C-peptide?

The most common cause is insulin resistance, seen in prediabetes, early type 2 diabetes, and metabolic syndrome, where the pancreas compensates by producing extra insulin. Chronic kidney disease raises C-peptide artificially because the kidneys normally clear it. Rarer causes include insulinoma, a benign insulin-secreting tumor, plus Cushing’s syndrome and certain medicines that stimulate insulin release. Your doctor interprets the value alongside glucose, kidney function, and your medication list.

Do I need to fast before a c peptide test?

Usually yes — most C-peptide tests are ordered fasting, typically 8 to 12 hours without food or caloric drinks, because eating triggers insulin release and raises the result. Plain water is generally fine. Some versions are deliberately non-fasting: random tests during a low-blood-sugar episode, or stimulated tests after a standardized meal. Follow the specific instructions on your lab order, and ask your care team if anything is unclear.

What is a normal C-peptide level in ng/mL?

Typical fasting values fall roughly between 0.5 and 2.0 ng/mL, though some laboratories use ranges closer to 0.8–3.1 ng/mL depending on their assay. Because methods and units differ between labs, the reference range printed on your own report is the one that counts. A result should also be read alongside the glucose level from the same draw, since blood sugar directly drives how much insulin — and C-peptide — the pancreas releases.

Can C-peptide tell type 1 from type 2 diabetes?

Often, yes — especially a few years after diagnosis. Persistently very low C-peptide points toward type 1, where autoimmune damage destroys insulin-producing cells. High or preserved C-peptide fits type 2, where the pancreas still produces insulin but the body resists it. Around the time of diagnosis, values overlap considerably, so doctors add autoantibody testing and clinical judgment. A robust C-peptide years after a type 1 diagnosis is reason to reconsider the label.

Why measure C-peptide instead of insulin directly?

Two reasons. The liver removes about half of the insulin the pancreas releases before it reaches a blood draw site, while C-peptide largely bypasses that filter, giving a truer measure of production. C-peptide also lasts about 30 minutes in blood versus just a few minutes for insulin, making it steadier to measure. In people who inject insulin, C-peptide has a third advantage: injected insulin contains none, so the test isolates the body’s own output.

Does injected insulin affect C-peptide results?

Yes, in two ways. Manufactured insulin contains no C-peptide, so it never inflates the result — that’s precisely why the test can separate your own production from injected insulin. Indirectly, insulin therapy lowers blood glucose, which quiets your own beta cells and can suppress your measured C-peptide. This suppression reflects resting cells, not necessarily lost ones. Always tell the lab and your doctor about insulin use so the result is interpreted correctly.

What does low C-peptide with low blood sugar mean?

It depends on the insulin level measured at the same time. Low glucose with high insulin but low C-peptide indicates the insulin came from outside the body — an injection — since injected insulin carries no C-peptide. Low glucose with both insulin and C-peptide low suggests insulin isn’t the cause at all, turning attention to hormone deficiencies, liver disease, alcohol, or illness. Capturing blood during an actual episode is essential for a clear answer.

References

• MedlinePlus: C-Peptide Test
• MedlinePlus Medical Encyclopedia: Insulin C-peptide Test
• Jones AG, Hattersley AT. The clinical utility of C-peptide measurement in the care of patients with diabetes (NIH/PMC)
• NIH NIDDK: Insulin Resistance & Prediabetes

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.