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Metabolic health testing: HbA1c, fasting insulin and what they miss

Headshot of Dr. Nikola Topalovic, MD PhD
Medically reviewed by Dr. Nikola Topalovic, MD PhD · Last reviewed 4 September 2026

By the time fasting glucose is abnormal, insulin resistance has usually been present for years. Measuring insulin as well as glucose is what turns a late diagnosis into an early one.

What people notice

  • Weight settling around the abdomen despite unchanged diet
  • Energy crash an hour or two after meals
  • Rising blood pressure and triglycerides
  • Skin tags or darkened skin in the neck folds
  • Fatty liver found incidentally on a scan

Symptoms overlap between causes. This list is a prompt to measure, not a diagnosis.

Markers worth measuring

HbA1c
Reflects roughly three months of average glucose. No fasting required, and the standard measure for diagnosing and monitoring diabetes.
Fasting glucose
A single point in time — useful, but the last thing to become abnormal.
Fasting insulin
The early marker. Rises for years while glucose stays normal, as the pancreas compensates.
HOMA-IR
Calculated from fasting glucose and insulin. A simple, usable estimate of insulin resistance.
Triglycerides and HDL
The triglyceride-to-HDL ratio is a strong, cheap surrogate for insulin resistance.
ALT, GGT
Elevated liver enzymes in a non-drinker often signal fatty liver, which travels with insulin resistance.
Uric acid, CRP
Both track with metabolic dysfunction and add to the risk picture.

Why insulin is the marker that gets skipped. Fasting insulin is not routinely rebated or routinely ordered, so most people never see it. Yet the natural history is well described: insulin rises first as tissues become resistant, glucose holds normal for years on the back of that compensation, and only when the pancreas can no longer keep up does glucose drift. Measuring both gives you a decade of warning instead of a diagnosis.

HbA1c's blind spots. HbA1c measures glycated haemoglobin, so anything that changes red cell lifespan changes the result. Iron deficiency and B12 deficiency push it up; haemolysis, recent blood loss, blood donation and some haemoglobin variants pull it down. In those situations the number can misrepresent actual glucose control, which is another argument for reading it with a full blood count and iron studies alongside.

The hormone connection. Insulin resistance and visceral fat lower SHBG and testosterone and raise aromatase activity, which is why the metabolic and hormone panels belong in the same draw. In men under 50 presenting with low testosterone, the metabolic picture is frequently the driver, and it is the one that responds to change.

What to do with the numbers. Metabolic risk is a conversation with your own doctor, particularly if HbA1c sits in the pre-diabetes band or above. Our report lays out the pattern in plain English, including the calculated HOMA-IR and triglyceride-to-HDL ratio, so that conversation starts from complete data.

FAQs

Do I need to fast for HbA1c?
No. HbA1c reflects three months of average glucose and can be drawn at any time. Fasting glucose, insulin and triglycerides on the same panel do require 8–12 hours.
What does fasting insulin add over glucose?
Years of lead time. Insulin rises long before glucose does, so it identifies insulin resistance while it is still easily reversible.
Can HbA1c be misleading?
Yes. Iron and B12 deficiency raise it; recent blood loss, donation, haemolysis and some haemoglobin variants lower it. Read it alongside a full blood count.
How often should I retest?
For most people, a baseline and then a repeat at three to six months after changing something. More frequent testing rarely adds information.

Measure it properly, in one morning draw.

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