Bone Density Test

In medical terms, bone density refers to the amount of matter per cubic centimeter of bones. Bone density is measured by means of a procedure known as densitometry, which is performed over the lumbar spine. It is painless and involves the least amount of exposure to radiation. Most commonly the bone density test is used for the diagnosis of osteoporosis.

Osteoporosis is a bone disease that results in an increase in the risk of fractures. An abnormality in the bone mineral density, disruption in the micro architecture of bones and a deviation in the proportion of non-collagenous proteins in bone, characterize osteoporosis. Advancing age, low bone mass, a sedentary lifestyle, smoking and drinking habits and a family history of osteoporosis form the major risk factors for this bone disease. In order to bring about an early detection of osteoporosis, a bone density test is advisable.

Women, who are in their post menopausal stage and have one additional risk factor for osteoporosis, should get a bone density test done. Women undergoing a hormone replacement therapy or those having a sustaining fracture are also advised to get the bone density test done. Apart from detecting osteoporosis, the bone density test also helps in predicting the risk of broken bones and determines the need for its treatment.

The DEXA scan is believed to be the most accurate bone density test. DEXA is short for dual-energy x-ray absorptiometry and can detect even a 1% change in bone density. The scan takes about ten minutes and exposes the patient to an amount of radiation that is less than that during a chest x-ray. During the test, the person lies in bed under a scanner and a plastic arm that radiates x-rays. The scanner then takes images of the patient’s body and the images are subject to comparison of the patient's bone strength with the desirable bone density values with respect to the age, lifestyle and risk factors of the patient.

The results of the bone density test are reported in terms of three parameters namely, the Z-score, the T-score and the density measured in grams per cubic centimeter.

A T-score compares the patient's bone density with the optimal peak bone density for the patient's gender. It is reported as the number of standard deviations, which are below the average value of the bone densities. A T-score that comes to a value grater than -1 is considered normal. If a patient scores between -1 and -2.5, he/she is diagnosed osteopenia and is considered being at the risk of falling prey to osteoporosis. A T-score of less than a -2.5 is diagnostic of osteoporosis. In short, a T-score is the number of standard deviations above or below the mean for a healthy 30-year-old adult of the same gender as that of the patient.

A Z-score is the number of standard deviations above or below the average for the patient's age and sex. It is used to compare the results of the patient with others of the patient's age, weight, ethnicity and gender. A Z-score is used to detect an unusual factor, if any, resulting in the bone loss of the patient. A Z-score of a less than -1.5 is diagnostic of other factors leading to osteoporosis. Thyroid abnormalities, malnutrition, negative side effects of certain medications or the consumption of tobacco are the probable factors leading to the diminishing bone density.

Bone density test is an excellent tool in the diagnosis of osteoporosis and is fairly accurate in predicting the risk of fractures. A bone density test can detect a low bone density but cannot tell the reason behind it. It remains with the patient, with the consultation of a medical practitioner to reflect on his/her lifestyle and assess his/her family history to find out the reason and act upon it.