Do you have three serves of dairy (or dairy-free equivalent) every single day?
Calcium deficiency is quite common and is a serious issue with potential long reaching health issues.
Adolescents (especially girls) and post-menopausal women are at a particularly high risk as these groups have higher calcium requirements than other gender and age groups (1300mg per day compared to the RDI for most adults of 1000mg per day).
You can't tell if you are calcium deficient, which is why osteoporosis is often called the silent killer . . . a blood test will not tell if you are not getting enough calcium.
Bone mineral density scans are a good indicator as calcium is leached from the bones if not enough is eaten (bone density is lower), but this is not an actual direct measure of calcium status.
It is important to also get your RDI of vitamin D as this is assists calcium to be absorbed.
If you don't believe that you are getting your RDI of calcium through food, then you could also take a calcium supplement . . . remember that calcium is essential for healthy, strong bones and teeth and is also required to maintain correct pH levels in your blood.