These look at specific markers in the blood such as bone alkaline phosphatase, calcium, phosphate which indicate the state of the bones. In osteoporosis these are all normal (ruling out other conditions such as Paget's disease of the bone), except when there has been a recent fracture when alkaline phosphatase, produced by osteoblasts, is raised.
These are used to diagnose fractures. In addition certain features such as cortical pencilling (where the outlines of the bone appear more vibrant due to the loss of ventral parts of the bone) are indicative of osteoporosis.
This is where X-ray beams are used to measure the bone mineral density (BMD). The principle method used is Dual Energy X-ray Absorptiometry (DEXA). The patient is placed in a scanner which moves over the whole body and the absorption of small amounts of X radiation by the bones indicates the amount of bone present. In total, the radiation dose to the patient is no more than spending a day in Cornwall! It does have some disadvantages, such as it is less accurate in very overweight or very underweight people. Degenerative conditions, such as osteoarthritis, where bone mass is lost not due to osteoporosis, can produce an artificially low result. However, at present it is the most accurate and precise tool available with the least radiation dose.
The report comes back with a reading called a T score which indicates how close to a normal peak bone mass the patient is. A T score of less than -1 is normal. Between -1 and -2.5 indicates the beginnings of bone loss (osteopenia). Less than -2.5 is indicative of osteoporosis.