A simple grip-strength test can reveal if people of normal weight have undetected metabolic syndrome, a potentially deadly condition that usually includes diabetes, high blood pressure, and high cholesterol.

According to University of Florida researchers, there are about 30 million Americans who are of normal weight but have high levels of body fat. They are known as “healthy-weight obese” or “skinny fat”and are unlikely to be screened for metabolic syndrome because from outward appearances they do not seem at risk.

For their study, researchers assessed a national survey that contained information on grip strength measurements, blood pressure readings, and blood sugar levels for nearly 1,500 adults whose body mass index (BMI) fell within the normal range.

Those with undiagnosed diabetes and high blood pressure had weaker grip strength than other healthy-weight individuals without the conditions, they found.

Researchers speculate that the reduced grip strength of those with hidden diabetes could be the result of lower muscle quality or a condition called “diabetic hand syndrome,” which limits finger movement.

Scientists are working to refine the test so that it can be used at home and in doctors' offices.