Bone mineral content of the spine with dual photon absorptiometry: normalization of the values

A Novo Industry BMC-LAB 22a densitometer equipped with a 153Gd source was recently implemented for the measurement of bone mineral content (BMC). 70 females (aged 16 to 86 years) and 67 males (aged 20 to 79 years) were selected to form a reference population. Care was taken to exclude patients with an illness or taking a drug that could influence the measurements, made at the lumbar spine level (L2-L4). Normalization procedures using several parameters (age, length, weight, span, lean body mass, an index of obesity, accepted scans) were developed to try and reduce the large interindividual coefficient of variation (CV). Total BMC values were found to yield a larger CV than when expressed as BMC cm-1. The relation of BMC with age showed a significant linear decrease of 0.3% year-1 for the male population. In the female population the BMC was not correlated with age up to the age of 50 years. Thereafter a linear bone loss of 0.76% year-1 was noted. Correcting for length decreased the CV in males and in females younger than 50 years. The use of the other parameters resulted in no or a very slight improvement. Combining parameters in a multiple regression analysis resulted in a significant decrease of the CV in females older than 50 years only.