HOMA-IR and the Kraft insulin test: seeing insulin resistance 10 years before diabetes

A normal fasting glucose is preserved until about 60% of pancreatic beta-cell function is already lost. If you want to see a metabolic problem before HbA1c climbs above 5.7%, there are two tools your physician should put next to your blood work: HOMA-IR and the Kraft insulin test.

Why fasting glucose alone hides the problem

The Whitehall II study (Lancet 2009) tracked over 6,000 people for 13 years before their type 2 diabetes diagnosis. Fasting glucose only starts rising 4–5 years before diagnosis, but insulin sensitivity begins declining 13 years earlier. That means for most of the “silent phase”, your glucose looks normal while insulin has to keep climbing to hold that norm in place.

This is exactly where HOMA-IR comes in.

HOMA-IR: two numbers, one equation

HOMA-IR (Homeostasis Model Assessment of Insulin Resistance), developed by Matthews et al. (Diabetologia 1985), combines fasting insulin and fasting glucose into a single index:

"HOMA-IR = (fasting insulin mU/L × fasting glucose mmol/L) / 22.5"

Ranges used in published studies vary by population and assay. The points below are illustrative comparisons, not diagnostic cut-offs:

• Some studies use lower HOMA-IR values to describe greater insulin sensitivity
• Higher values have been associated with lower insulin sensitivity, but there is no universal international diagnostic cut-off

International laboratory guidance does not recommend routine insulin measurement to assess diabetes or cardiovascular risk in the general population. HOMA-IR and fasting insulin are supportive measures alongside the clinical picture.

HOMA-IR needs only one fasting draw, is inexpensive, and you can compute it yourself. Its limit: once the pancreas is exhausted (beta-cell function falling, insulin deficient), the formula can look falsely normal. For those cases we have a more precise, more demanding test.

The Kraft insulin test: a slow 5-hour walk

Dr Joseph Kraft published “Detection of Diabetes Mellitus In Situ (Occult Diabetes)” in 1975, based on glucose and insulin curves in over 14,000 patients after a 100 g glucose load. A standard oral glucose tolerance test (OGTT) tracks the glucose response; the Kraft test tracks the insulin response in parallel. What emerges is an insulin curve whose shape says more than the glucose curve.

Kraft classified five patterns. Only pattern I is truly normal – insulin peaks at 0.5–1 h and returns to baseline by 2 h. Patterns II–V represent progressive dysfunction: delayed peak, exaggerated peak, prolonged decay. The clinically most relevant in the Kraft database were patterns III–V in patients whose glucose curves were perfectly normal – occult hyperinsulinaemia (Crofts et al., BMJ Open Diabetes Res Care 2016).

"Kraft historically used the phrase “diabetes in situ.” His classification is not a stand-alone diagnostic standard: an unusual insulin curve may indicate higher risk, but it does not confirm disease."

The full Kraft protocol is rarely done in Estonian clinics because it requires 5 hours and 4–5 insulin draws. In practice we use a shorter modification: OGTT plus insulin at 0, 60 and 120 min. That captures most of the meaningful patterns.