Standardization of BMD

The three manufacturers of DEXA equipment do not give STANDARDIZED RESULTS. The differences are clinically important, making it difficult to compare a measurement made from one machine to the other. For example, the hip bone density on a Lunar scan is about 6% higher than on a Hologic scan. If the physician must try to compare studies done on different machines, the best way is to apply the following equations:

TOTAL HIP
First Measurement Hologic Lunar Norland g / cm2	Second Measurement Hologic Lunar Norland g / cm2

--- mg/cm2	--- mg/cm2
--- % change

LUMBAR SPINE
First Measurement Hologic Lunar Norland g / cm2	Second Measurement Hologic Lunar Norland g / cm2

--- mg/cm2	--- mg/cm2
--- % change

These are the equations:
sBMD = 1000 (a + b x BMD)
Manufacturer Parameter Femoral neck Trochanter Total hip
Hologic a 0.019 -0.017 0.006
b 1.087 1.105 1.008
Lunar a -0.023 -0.042 -0.031
b 0.939 0.949 0.979
Norland a 0.006 0.057 0.026
b 0.985 0.961 1.012

Reference: Y.Lu, T.Fuerst, S.Hui and H.K.Genant, Standardization of Bone Mineral Density at Femoral Neck,Trochanter and Ward's Triangle, Osteoporos Int (2001)12:438-444.

Manufacturer	Parameter	Femoral neck	Trochanter	Total hip
Hologic	a	0.019	-0.017	0.006
b	1.087	1.105	1.008
Lunar	a	-0.023	-0.042	-0.031
b	0.939	0.949	0.979
Norland	a	0.006	0.057	0.026
b	0.985	0.961	1.012

Spine

Hologic: 1.0550 (BMD - 0.972) +1.0436
Lunar: 0.9683 (BMD - 1.100) + 1.0436
Norland: 0.9743 (BMD - 0.969) + 1.0436

Using these equations, the average error using standarized BMD for an individual patient was 3.5%. Reference: Hui, SL, et al. Universal Standardization of Bone Density Measurements: A Method with Optimal Properties for Calibration Among Several Instruments. J Bone Mineral Research 1997;12:1463-70.

Updated 10/20/05 - a reader noted an error in the conversion for Norland spine, which was corrected