About the OST osteoporosis screening index
This calculator implements the OST (Osteoporosis Self-Assessment Tool) index, a simple weight-and-age screening formula developed to flag people who may benefit from a bone density scan. It is one of the simplest validated osteoporosis screening tools in the clinical literature, requiring only two measurements. This page is intended for educational and informational use and does not diagnose osteoporosis or replace a bone density (DXA) scan.
How the OST index is calculated
The formula is: OST index = 0.2 x (weight in kilograms - age in years), with the result truncated to a whole number. Because lower body weight and older age are each independently associated with lower bone mineral density, subtracting age from weight and scaling the difference produces a single number that trends lower (more negative) as osteoporosis risk rises. This calculator accepts weight in pounds and converts it to kilograms (1 lb = 0.453592 kg) before applying the formula.
Reading the risk bands
- OST index above -1: Low risk on this screening tool.
- OST index -1 down to -4: Moderate risk.
- OST index below -4: High risk, generally warranting a bone density scan if one has not been done.
The calculator also reports body mass index (BMI) and a simple count of three well-known clinical risk factors for osteoporosis - a prior fragility fracture after age 50, a parent's hip fracture, and current smoking. These are shown for context; they are not added into the OST index itself, since the OST formula uses only weight and age.
Important disclaimer
The OST index is a screening aid, not a diagnosis. It was derived and validated mainly in postmenopausal women, and results in other groups should be interpreted cautiously. A DXA bone density scan remains the standard for diagnosing osteoporosis. Discuss your result, and any risk factors present, with a healthcare provider before making decisions about testing or treatment.