The Overlooked Biomarker A Cardiac Surgeon Wants More People To Test
Jeremy London, M.D., is a cardiovascular surgeon who has spent decades operating on blocked arteries. He exercised regularly, ate well, didn't smoke, and kept his blood pressure in check. By every standard measure, he looked like someone who would never have a heart attack. Then one day, he started experiencing chest pain and shortness of breath, and by the time he went to the hospital his artery was 99% blocked.
As a heart surgeon, London was up to date on all the recommended screenings and bloodwork based on his age and identifiable risk factors. But it wasn't enough to catch London's heart disease early enough. Two years later, after putting on a continuous glucose monitor at his son's suggestion, London learned insulin resistance was very likely the hidden driver of his heart attack. He only uncovered the root cause through measuring metabolic biomarkers standard blood tests don't include.
The CGM experiment that changed everything
About two years after his heart attack, London still didn't feel like he completely understood what caused his heart attack. His son Max suggested he try wearing a continuous glucose monitor (CGM) and see what it shows. London agreed, half-expecting to prove what a great job he was doing with his diet and fitness.
Within 48 hours, London could see that his glucose levels were chronically elevated, regardless of what he was eating and whether was fasting. He realized his hemoglobin A1c drawn and fasting insulin levels had never been checked. His standard labs had only ever included fasting glucose, and those numbers never raised a red flag.
Fasting glucose is a snapshot measuring the amount of sugar in your blood after an overnight fast, but hemoglobin A1c and fasting insulin produce a more complete picture.
Hemoglobin A1C measures the percentage of red blood cells that have glucose attached to them, reflecting your average blood sugar over the past two to three months. Fasting insulin measures how much insulin you produce after an overnight fast.
When London showed his CGM readings to his internist, the doctor told him to get his hemoglobin A1c tested the next day. His hemoglobin A1c came back at 5.9, which is high-end pre-diabetic. Having the CGM insights led him on the right path to catch something years of standard bloodwork had missed entirely.
Why your labs look normal, even when something is wrong
London explains how his story is the perfect example of how measurements like fasting glucose can "within normal limits" while insulin resistance is already building in the background. In fact, insulin resistance (and an elevating fasting insulin) is believed to precede type II diabetes by 10 to 15 years..
"Our pancreas is an incredibly resilient and efficient organ. It keeps up for a long time. Your hemoglobin A1c may be totally normal, and your fasting glucose may be totally normal, but your insulin level is unacceptably high," he says.
In other words, your pancreas keeps pumping out more and more insulin to manage glucose that isn't being processed efficiently. The glucose numbers stay in range, so your labs look fine. But the insulin required to keep them there is climbing. Chronically high insulin from insulin resistance promotes vascular inflammation1, which accelerates the buildup of plaque in artery walls.
Research supports this picture. A study published in PLOS Medicine2 found that fasting insulin was a stronger predictor of coronary heart disease and stroke risk than fasting glucose or hemoglobin A1c in women with normal glucose levels. A separate meta-analysis of more than 26,000 non-diabetic adults3 linked elevated fasting insulin to increased risk of cardiovascular and all-cause mortality.
Testing your fasting insulin
London's full picture of cardiovascular risk goes well beyond a standard comprehensive metabolic panel (which only includes fasting glucose for blood sugar insights), and he is confident fasting insulin is going to be the next routine heart test. While no major guidelines currently recommend universal fasting insulin screening, he believes that is going to change. He aims to have a fasting insulin level of 5 or less.
London recommends getting fasting insulin checked at the same lab over time, and tracking the trend. Because different labs can return different results for the same sample, London recommends going to the same lab each time, and treating fasting insulin as a relative scale rather than a fixed number.
"You wanna weigh on the same scale every day," he said. "You don't wanna go get an insulin level checked in one lab and then get it checked in another."
What else to test for
London's own post-heart attack labs told a complicated story. His ApoB came back at 180, far above the target of 80, so he went on Repatha, a cholesterol-lowering injectable. The medication wasn't enough on its own, so he's since made significant dietary changes and is considering adding a statin depending on his next particle count.
His experience mirrors what he sees in patients—standard labs often look reassuring, while the real risk is hiding in numbers no one thought to check. Here's what he looks at, and where he wants the numbers to land for primary prevention.
- Fasting insulin: London's target is 5 or less. Use the same lab each time to track trends accurately.
- Hemoglobin A1c: London aims for 5.5 or less. Even small changes matter here. A shift of 0.1 or 0.2% is significant because the range before crossing into pre-diabetic territory is narrow.
- ApoB: London's target is under 80. ApoB measures the number of artery-clogging particles in your blood, a more precise picture of cardiovascular risk than total LDL cholesterol alone. "Many times we see people with low normal LDLs that have really high levels of atherogenic ApoB," he noted.
- Lp(a): A genetically controlled lipoprotein that can significantly elevate heart disease risk. London's own Lp(a) was near zero, which he considers fortunate. If yours is elevated, the strategy is to control every other modifiable risk factor as aggressively as possible.
- Fasting glucose and triglycerides: Still useful as part of the broader picture, alongside total cholesterol.
The takeaway
Heart disease isn't something that happens suddenly. For most people, it happens under the surface for years, which means the real leverage over heart disease is in catching it earlier than a standard cholesterol panel ever will.
The practical takeaway here is simple. Ask your doctor to add fasting insulin to your next metabolic panel. It requires a blood draw after an overnight fast, and while it may not be on your doctor's standard order form, most labs can easily run it. However, there's still the question of whether insurance will cover it, so be sure to ask to avoid surprises. Pair it with hemoglobin A1c and ApoB and track your numbers at the same lab over time so you can act on the trend instead of waiting for a wake-up call.