The Fasting Glucose Comeback: Why an Old Test Still Wins for High-Risk Families

The study, published in BMJ Open Diabetes Research & Care, followed 583 adults from a Hong Kong workforce cohort first assessed between 1998 and 2003 and reassessed roughly 12 years later. About 40% of them had a family history of young-onset type 2 diabetes (a parent or sibling diagnosed before age 40), a group the researchers call FmH-YOD. The question: does adding a 1-hour glucose reading from a standard OGTT meaningfully sharpen prediction in that high-risk group, the way it does in the general population?

The answer, per the Hong Kong analysis, is more nuanced than the wellness shorthand suggests. Both family history and a high 1-hour glucose independently predicted who'd later develop diabetes — but the two risk factors interacted negatively, meaning the predictive bang you get from adding a 1-hour reading is smaller in the family-history group than in everyone else. Practically speaking: when your baseline risk is already loaded by genetics, the fancier test buys you less new information.

Among the 583 participants — median age 41, mostly lean by Western standards with a median BMI of 23.3 — 99 (about 17%) had developed diabetes by follow-up. Split them by family history and the picture sharpens. In the family-history group, 45% of those with a high 1-hour glucose progressed to diabetes, versus 17% of those with a normal 1-hour glucose. In the no-family-history group, the same split was 16% versus 1.8%, according to the study.

Notice what jumps out: a family-history participant with a normal 1-hour glucose still had a 17% chance of developing diabetes — roughly the same risk as someone without family history but with an elevated 1-hour reading. In other words, a reassuring OGTT result didn't reassure very much in the high-risk group. The genetics were doing a lot of the talking.

That's where fasting glucose re-enters the chat. In the receiver-operating-characteristic analysis the authors ran to compare tests head-to-head, the 1-hour glucose's discriminative performance dropped in the family-history subgroup, while plain fasting plasma glucose outperformed it for predicting incident diabetes in that same group. The older, cheaper, less-trendy measurement won where it arguably matters most.

A few honest caveats before anyone reorganizes their next physical. This is a single observational cohort of fewer than 600 people, drawn from one Hong Kong workforce, and the confidence intervals around some of the headline odds ratios are wide — the combined family-history-plus-high-1-hour group, for instance, carried a 28-fold odds of incident diabetes but with a confidence interval spanning roughly 5 to 146, per the published estimates. That's a strong signal with imprecise edges.

It also doesn't mean the 1-hour OGTT is overrated in general. International groups have been pushing the test precisely because it catches dysglycemia that fasting numbers miss in average-risk adults — and this study doesn't contradict that. What it does suggest is that which test is most informative depends on who's being tested. Add strong family history and the calculus shifts.

There's a tidy logic to it. A 1-hour glucose spike is largely a story about how your pancreas and tissues handle a sugar load right now. A fasting number is closer to a long-run summary of your baseline metabolism. In people whose biology is already nudged toward early diabetes by inherited factors, that baseline drift may simply show up earlier — and more legibly — in a fasting draw.

The takeaway isn't to skip any test, and it certainly isn't to self-diagnose from a single number. It's to know which questions you're actually asking your bloodwork to answer. If a parent or sibling was diagnosed with type 2 diabetes before 40, that fact is itself a major piece of information — and the new data suggest your fasting glucose deserves close attention rather than being dismissed as old-fashioned. A clinician who knows your family history is best placed to decide what to order, how often, and when to add hemoglobin A1c or an OGTT to the picture.

For everyone else, the broader point still holds: family history is data. So is a fasting number you've been ignoring on the lab printout because your 1-hour glucose looked fine.