There is an inverse relationship between Z-scores and the presence of causes of secondary osteoporosis.
However only a small difference in mean Z-scores of 0.3 between those with
and without secondary causes of osteoporosis was detected
[17].
Indeed, a study done in Singapore found that the traditional
Z-score value of 2 as an indicator of patients with
secondary cause of osteoporosis performed abysmally with a
sensitivity of less than or below 20.7% for both males and
females. Using a Z-score of 1 gives a sensitivity of 71.7%
in females and 59.1% in males. The specificity was 37.8%
and 35.3% respectively [5]. Moreover, the Z-score is obtained
from comparison of the patient's BMD to the mean BMD of a
cohort consisting of people in the same age range as the patient.
This is as opposed to the T-score where the comparison
is against the peak BMD of the cohort. In the oldest old, this
might at times not be possible as there were insufficient
volunteers in the age range to calculate the mean BMD in that
age range.