My latest thinking on blood tests
If you’ve been following my work for a while, you know that my absolute highest priority is getting you the right data so I can build the most effective strategy for your health. I don't care what’s easy. I care what actually works.
For a long time, I viewed the Oral Glucose Tolerance Test (OGTT) as a powerful tool for catching early metabolic issues. It makes sense on paper: you drink a heavy dose of sugar, and the test measures how your body responds. Your blood sugar shows how well your insulin is working, and the test is standardized, so I thought it was the gold standard.
But as I do more research (and thanks to Denis Champagne asking good questions), my thinking has evolved. I no longer recommend the OGTT for routine metabolic screening for my clients over 45.
Here is why I've changed my approach and the exact test panel I am switching to.
Get my bloodwork request sheet
First, if you want my updated blood-request sheet, download it from Papermark. It tells you everything you need to know.
Now for why I have changed ...
The real problem with standard lab tests
Most people think a good fasting glucose or a low HbA1c number means they aren’t insulin resistant. That’s not true.
Fasting glucose never tells an accurate story. When your cells start to resist insulin, your pancreas makes more insulin to push glucose into them, and your fasting glucose stays under 100 mg/dL [5.6 mmol/L]. That can go on for years. By the time it reaches the prediabetic range of 100 to 125 mg/dL [5.6 to 6.9 mmol/L], your pancreas has been pumping out extra insulin for a long time. A normal fasting glucose only tells you that your pancreas is still keeping up.
HbA1c measures your average blood sugar over about three months, not insulin resistance. If you’ve reduced carbs in the last few months, you can be severely insulin resistant and still have a "perfect" A1c number. It shows your blood sugar, not how hard your pancreas is working to keep it there.
So, why not just use the OGTT?
This is the part I didn’t know: the OGTT is a dynamic stress test. It is strongly affected by everything you do in the prior 24 hours, and even at the clinic you can get different results under different conditions. The OGTT has a reproducibility rate of only about 65% to 75%. In one study of 354 adults, repeating the glucose tests about six weeks later put more than a quarter of them in a different category.
Your body secretes insulin based on certain variables: how well you slept the night before, whether you had a stressful drive to the lab, or how hard you worked out 24 hours prior. Even worse, if you are a health-conscious person who eats fewer carbs, a sudden 75-gram tidal wave of sugar will cause a massive, temporary blood-sugar spike. The standard instructions tell you to eat at least 150 grams of carbs a day for three days before an OGTT to prevent this. If you skip that step, you can get a false positive.
I needed something better. I needed a test that is stable and accurate.
The new test: the NMR LipoProfile + fasting C-peptide
Moving forward, I am requiring a specific two-part panel for metabolic screenings. The new test combines the NMR LipoProfile® with Lipids and Insulin Resistance (IR) Markers and a Fasting C-Peptide test. I still want your fasting glucose and HbA1c from the same draw. I can only read your C-peptide next to your glucose.
Instead of measuring how you handle one big dose of sugar on one morning, this panel measures both sides of your metabolism:
The LP-IR Score uses nuclear magnetic resonance (NMR) to measure the size and number of the particles that transport fat and cholesterol in your blood. Those particles change in a recognizable pattern as insulin resistance develops, so the score gives a useful estimate of how well your tissues respond to insulin.
The Fasting C-Peptide tracks how much insulin your pancreas is pumping out. Your pancreas makes one molecule of C-peptide for every molecule of insulin. Your body releases insulin in rhythmic pulses every 5 to 15 minutes, and your liver removes a varying share of it before your blood reaches your arm, where the lab draws it. A single fasting insulin reading can easily catch you at a natural peak or trough. C-peptide passes through the liver untouched and stays in your blood about six times longer than insulin, so one reading averages out those pulses and gives a steadier look at your pancreatic strain.
Why this panel works better
It’s harder to skew: Lipoprotein sizes and C-peptide levels reflect what you’ve eaten over the past several days, so a stressful drive to the lab won’t throw them off. A sudden change in diet the week before will move both numbers, which is why the protocol below matters.
It’s a single draw: No sitting in a lab waiting room for 2 hours feeling nauseous from a syrupy glucose drink. You walk in, get one draw, and walk out.
Understanding your results: what to look for
When the results come back, I will be looking at these two key metrics to see exactly where your cellular health stands:
1. The LP-IR score (scale of 0 to 100)
Optimal (less than 30): You are highly insulin sensitive. Your tissues are absorbing nutrients efficiently, your pancreas is under very low strain, and your metabolism is operating beautifully.
Moderate risk (30 to 45): You have early, hidden insulin resistance. Your body is managing to keep blood sugars stable, but your liver and fat cells are beginning to resist insulin, signaling that it is time to optimize lifestyle factors.
Insulin resistant (46 to 67): You have significant insulin resistance. Your metabolism is under heavy stress, and we need to take targeted action to reverse it before it progresses further.
High (68 and above): Labcorp flags this score as elevated insulin resistance with increased diabetes risk. We need to act now.
I use tighter targets than Labcorp, because I want you fully insulin sensitive. In the study that validated the score, middle-aged and older adults without diabetes averaged 43, so many people who feel fine will score above 30. Labcorp offers the score, and the FDA has not cleared it, so I read it alongside your other numbers. Niacin lowers the score, and high triglycerides from alcohol or genetics raise it, so tell me if either applies to you.
2. Fasting C-peptide
Optimal range (0.5 to 1.5 ng/mL [in Europe, it’s 0.17 to 0.50 nmol/L]): Your pancreas is operating efficiently without overworking.
Elevated (greater than 1.5 ng/mL [0.50 nmol/L]): Even if your blood sugar looks normal, your pancreas is working overtime to pump out extra insulin just to hold your baseline together. Again, this requires action.
My targets are tighter than the lab’s. Labcorp calls 1.1 to 4.4 ng/mL normal. Quest calls 0.80 to 3.85 normal on its standalone C-peptide test and 0.68 to 2.16 normal on its insulin resistance panel. Your report may flag a result I consider optimal as low, or call a result normal that I consider elevated. Read your result against my ranges instead of the lab’s flags.
A low C-peptide is good news only when your fasting glucose and A1c are normal. If your C-peptide is low while your blood sugar is high, your pancreas may not be making enough insulin, and you need to see your doctor.
Your kidneys clear C-peptide, so reduced kidney function raises it whatever your pancreas is doing. I check your creatinine before I read your C-peptide.
Cost and insurance
These tests are affordable. If you want to bypass the insurance headache entirely, you can order both through an online lab broker. Walk-In Lab lists them at about $180 combined, and some brokers charge less. You order the tests online, a network doctor signs the order, and you walk into a local Labcorp. Walk-In Lab doesn’t sell these tests in New York, New Jersey, Maryland, or Rhode Island.
If you prefer to use insurance, check with your insurer first. Medicare and some insurers cover these tests when you have a qualifying diagnosis, and others, such as Medica and Blue Shield of California, won’t pay for the NMR test at all. Without a diagnosis on the order, insurance will instantly reject it as a routine "screening" for a healthy person.
To save money, ask your doctor to order Labcorp test 123638 (NMR LipoProfile with Lipids and Insulin Resistance Markers) and Labcorp test 010108 (C-Peptide). Add Labcorp test 001453 (HbA1c) and Labcorp test 322000 (Comprehensive Metabolic Panel, which includes fasting glucose and creatinine) if they aren’t already on the order. Quest doesn’t offer the NMR LipoProfile. If you have to use Quest, ask for the Cardio IQ Insulin Resistance Panel with Score (test 36509), which includes C-peptide but gives no LP-IR score. I highly recommend Labcorp.
If you have metabolic syndrome, prediabetes, high cholesterol, or a strong family history of early cardiovascular disease, ask your doctor to put that diagnosis on the order. With one of those diagnoses on the order, insurance may cover it.
The protocol: how to get the best results
To ensure your data is entirely accurate and reflects your true metabolic baseline, you must follow this exact protocol before your blood draw:
2 Weeks Before: Eat the way you normally eat. Don’t start a new diet, a cleanse, or a fast. If you eat low-carb, stay low-carb and tell me, so I can read your results with that in mind. Prepare the same way every time you retest, so we can compare your results.
3 Days Before: Stop taking biotin, including any hair, skin, and nail supplement that contains it. High doses of biotin distort the C-peptide test.
48 Hours Before: No intense workouts. Avoid heavy weightlifting or exhausting cardio for two days before the test. A hard workout changes how your body processes insulin for up to 48 hours.
The Night Before: Sleep and Fast. Prioritize a solid 7–8 hours of sleep. Fast for 14 hours before your draw. For an 8 AM appointment, finish dinner by 6 PM. You may drink plain water, but absolutely no coffee, tea, supplements, gum, or smoking the morning of the test.
Your Medications: Ask your doctor whether to take your usual morning medications, and tell me everything you take. GLP-1 drugs, diabetes drugs, and cholesterol drugs all change these numbers.
The Morning Of: Go early. Book your appointment between 7:30 AM and 9:00 AM to align with your natural circadian rhythms. Sit quietly in the waiting room for 5 minutes before they call you back to ensure your stress hormones are calm.
Next week: What to do about your new insulin resistance scores.
Once you have your bloodwork completed, book your 90-minute strategy call with me and let’s get you on the most efficient path to a healthy future. Reply to book that meeting.