[Daily clinical practice: Biological testing in osteoporosis].

Although biological testing has nothing to do with the diagnosis of osteoporosis, it can help the physician to: 1) identify secondary causes of low bone mass and/or fracture. There is however currently no consensus to define the biochemical parameters to be measured in this case. The cost-effectiveness of the biological evaluation, that is, measuring a minimum of parameters to detect a maximum of anomalies needs to be considered. Most experts agree that malignancy and especially a myeloma should be ruled out, and that an evaluation of calcium/phosphorus metabolism including the measurement of serum calcium, phosphate, PTH and 25 hydroxy-vitamin D should be performed. This allows to detect many anomalies including two very frequent conditions, primary hyperparathyroidism and vitamin D deficiency. Note however that complementary testing is generally needed to identify other diseases; 2) evaluate efficacy and observance of some osteoporosis treatments especially oral bisphosphonates. In this case, the evolution of the blood or urine level of some markers of bone turnover over a 3-6 month period after the initiation of therapy will be considered. For example, a decrease of more than 30% in the serum concentration of CTX (C-terminal telopeptide of type I collagen) will be regarded as a significant change indicating that treatment has reduced bone resorption.