High prevalence of laboratory abnormalities indicative of secondary osteoporosis detected by systematic testing

Osteoporosis treatment guidelines recommend assessment for potential causes of secondary osteoporosis, however, there are limited data evaluating the yield of laboratory tests recommended for routine screening. The purpose of this study was to quantify the frequency of abnormal laboratory results indicative of secondary osteoporosis in patients referred to a Metabolic Bone Clinic with a diagnosis of low bone density or fracture. A retrospective chart review was conducted on 890 consecutive patients at a tertiary academic medical center from October 2018 to December 2021. Upon referral, patients were asked to complete a standardized set of laboratory tests, including comprehensive metabolic panel, 25OHD, PTH, thyroid testing, complete blood count, phosphorus, tissue transglutaminase antibodies, and 24-h urine calcium with creatinine. Among 890 patients, 67% of subjects had at least one laboratory abnormality. The most common abnormalities were of 25OHD and PTH with 22.4% and 19.1% of each test respectively showing abnormal results. Over 99% of serologic testing was completed; however, urine calcium testing was completed in only 34% of subjects. Among individuals who completed 24-h urine calcium testing (<i>n</i> = 304), 26.5% had hypocalciuria (<100 mg/24 h), and 25.2% had hypercalciuria (>250 mg/24 h). Subjects with a Z-score <-2.0 were more likely to have abnormal laboratory results. This study demonstrates that laboratory abnormalities indicating secondary osteoporosis are very common among patients with low bone density and fracture. Systematic laboratory testing with a circumspect number of tests is appropriate in all patients with skeletal fragility.