Osteopenia is a clinical term used to describe a decrease in bone mineral density (BMD) below normal reference values, yet not low enough to meet the diagnostic criteria to be considered osteoporotic. BMD is diagnosed via dual-energy x-ray absorptiometry (DXA) bone scans. Osteopenia, as defined by the World Health Organization (WHO), is a t-score between -1 to -2.5, while values less than -2.5 are diagnostic for osteoporosis. Decreasing BMD values are reflective of an underlying disruption in the microarchitecture of bone and osteopenia, and osteoporosis is considered quantitative, not qualitative, disorders of bone mineralization. 
Bone mineral acquisition from birth to adulthood follows a predictable trend specific to an individual’s age and sex. With the onset of puberty, bone mineral accretion increases to its maximum level not long after peak height gains are achieved in adolescence. Bone mineral accretion rates remain the greatest for males and females for about four years after the peak accretion rate is achieved, and 95% of the adult bone mass is typically achieved by age 17 for females and 21 for males. Thus, peak bone mass is normally achieved by the third decade of life. Failure to achieve peak bone mass as a young adult results in early-onset conditions of decreased bone mass (osteopenia or osteoporosis) and increased risk of fragility fractures even in adolescence and young adulthood. After age 30, there is a gradual and natural bone mass reduction that takes place over the ensuing decades into later life. 
While it is estimated that heritable factors dictate up to 80% of our ability to achieve and maintain optimal bone mineralization levels, modifiable factors attributed to the rate of natural bone mass reduction into adulthood include weight-bearing exercises, nutrition status (adequate calcium and vitamin D daily intake), body mass, and hormonal milieu.
The natural bone loss that occurs gradually during adulthood is considered to be the cause of primary forms of osteopenia and osteoporosis. Secondary causes serve to accelerate this process and include lifestyle factors such as alcohol use disorder, smoking, sedentary lifestyle, thin body habitus (BMI under 18.5 kg/m2). White and Asian races are also established risk factors.
Overall disease states and certain medications are considered secondary causes as well. Medical conditions include hyperparathyroidism, anorexia, malabsorption syndromes, hyperthyroidism, chronic renal failure, hypogonadism, amenorrhea/oligomenorrhea, early onset menopause, and chronic conditions resulting in calcium and/or vitamin D deficiencies. Medications implicated in the disease process include excess glucocorticoids/long-term steroid use, valproic acid, proton pump inhibitors, antiepileptics, and chemotherapy agents. 
Currently, 34 million Americans are afflicted with osteopenia. The incidence is expected to exponentially increase as our population becomes older with each ensuing decade. Between 2010 and 2030, the United States population over 65 years of age is expected to increase from 13% to over 20%. By 2020, projections estimate that over 47 million Americans will be afflicted with osteopenia. 
Overall, females have a four-fold higher overall prevalence of osteopenia compared to males. However, males are more likely to demonstrate secondary causes of decreased bone mass. While secondary osteopenia and osteoporosis can develop at any age, the incidence of osteopenia in select subgroups demonstrates predictable patterns and trends. In the United States, 54% of postmenopausal women are osteopenic, and an additional 30% are already considered osteoporotic. By age 80, this relative trend predictably shifts in favor of osteoporosis as 27% of women are osteopenic, and 70% are osteoporotic.
Worldwide, Asia has reported the lowest average t-scores by region. Australia reported an incidence rate of osteopenia in 42% of men and 51% of women. In 2005, India reported a 52% overall incidence in its population. Perhaps more important than the population-based absolute BMD values reported is the associated burden of disease, which has been demonstrated in the reported fragility fractures by region worldwide. The greatest number of fragility fractures occur in Europe, followed by the Western Pacific region, Southeast Asia, and the Americas.
Fragility fractures significantly compromise a patient's quality of life and financially devastate the healthcare system. Roughly 2 million fragility fractures occur each year in the United States alone, and by 2025 this number is expected to increase to over 3 million. Worldwide, 9 million fragility fractures occur each year. The overall impact of fragility fractures on the healthcare system is staggering. In 2005, direct costs of care associated with fragility fractures alone tallied $19 billion, and the direct and indirect costs of care are expected to surpass $25 billion by 2025. In addition, fragility fractures significantly decrease the quality of life, and hip fractures alone are associated with a one-year mortality rate of greater than 20%. 
Osteopenia occurs secondary to uncoupling of osteoclast-osteoblast activity, resulting in a quantitative decrease in bone mass. Peak bone mass is typically achieved by males and females just prior to or early on in the third decade of life. Beyond age 30, bone resorption gradually becomes favored as dynamic bone remodeling continues into later decades of life. 
Histologic specimens demonstrate markedly thinned trabeculae, decreased osteon size, and enlarged haversian and marrow spaces. 
Bisphosphonates are the most commonly prescribed medication class for treatment. Adverse side effects are well documented in the literature as prolonged use has been linked to two major clinical side effects: osteonecrosis of the jaw (ONJ) and the atypical subtrochanteric femur fracture.
ONJ is rare and is associated with intravenous forms and not oral forms of the medication. Treatment entails immediately stopping the offending agent. Atypical femur fractures also are rare but have significant associated morbidity, and clinicians are cautioned against the chronic, uninterrupted bisphosphonate use beyond 3 to 5 years or in situations when patients report mild thigh discomfort while undergoing treatment. 
History and Physical
A comprehensive history and physical includes eliciting potential risk factors attributable to secondary bone loss. A thorough social history also should be obtained with attention to smoking history and chronic alcohol consumption. A family history of osteoporosis also should be noted. The patient should be asked about any prior fractures with focus given to low energy ground-level fall mechanisms and any fractures after the age of 40.
The physical exam is often normal except in certain cases of advanced disease states (i.e., osteoporosis). In healthy individuals without risk factors, most clinicians recommend women approaching menopause (or by age 65 years at the latest) and males at the age of 70 to be screened via a dual x-ray absorptiometry (DXA) scan. However, it should be noted that the United States Preventative Services Task Force (USPTF) has not found sufficient evidence to establish official screening recommendations for men, and systematic population-based screening for osteoporosis has yet to be implemented. 
Much attention should be given to the patient sustaining a fragility fracture, and early follow-up with an appropriate practitioner is highly encouraged. Although a standardized follow-up protocol is yet to be recommended, automated follow-up systems and fracture liaison services are two increasingly popular strategies to help improve on the historically reported and strikingly low follow-up rates of 1% to 10%.
Women with normal DXA scans do not need follow-up DXA scans, as studies have shown that most women with normal scores did not progress to osteoporosis. Some experts may advocate for follow-up scans upon treatment implementation, but this modality remains controversial as the literature suggests subsequent DXA scans have rarely resulted in interventions or treatment adjustments. 
The WHO has established DXA scans as the gold standard for assessing BMD levels. DXA scans utilize a single x-ray beam to measure calcified tissue in select regions of the body. Measurements are reported with 1% to 2% precision rates, and DXA scans are considered the most accurate diagnostic imaging modality with the least amount of radiation exposure. The lumbar spine (L2 to L4), the hip (compiled from the femoral neck, trochanters, and intertrochanteric regions), and the wrist are routinely included in the scan. The BMD reported reflects the absolute, patient-specific score determined from these measured anatomic areas.
In addition, the scan also reports a t-score and a z-score. The t-score is measured in standard deviations and reflects the difference between the patient's measured BMD and the mean value of BMD in healthy, young, matched controls (30-year-old women). By definition, a normal BMD measurement is within one standard deviation of the young adult mean. The WHO defines t-scores between -1 and -2.5 as osteopenic and scores below -2.5 as osteoporotic. The z-score is also measured in standard deviations, but the z-score is compared to a healthy, age-matched control group. The z-score is most clinically relevant when obtaining a DXA scan in younger patients when secondary osteoporosis is being considered. A z-score less than -1.5 warrants a comprehensive secondary osteoporosis workup.
Standard laboratory workup includes checking calcium, phosphorus, albumin, alkaline phosphatase, liver function tests, creatinine (serum and urine), 25 hydroxyvitamin D, TSH and free T4, and intact PTH levels. Males should have a free testosterone level checked to rule out hypogonadism.
The routine use of checking bone turnover markers (BTM) is debated. The utility of obtaining markers of bone resorption can be considered if this is being considered the possible underlying cause of secondary osteoporosis. Although reports question the reproducibility of such values, available tests include checking serum or urinary cross-links of type I collagen (deoxypyridinoline), N-telopeptide of type I collagen (NTx), or C-telopeptide of type I collagen (CTx).
The WHO created a fracture risk assessment tool (FRAX score) to predict the 10-year risk of sustaining a hip or other major osteoporotic fracture. These other major fragility fractures include fractures of the spine, wrist, forearm, or humerus. The assessment includes 12 questions weighted by the relative risk associated with a future fragility fracture event. Assessment includes age, sex, personal history of fracture, low BMI, oral steroid use, secondary osteoporosis, parental history of hip fracture, smoking status, and alcohol intake. In addition, optional BMD measurement values can be included from a prior DXA scan (if available) to provide a more comprehensive score report. 
The utility of the FRAX score is emphasized, especially in the osteopenic patient. Although fracture risk increases with decreases in BMD, the concept that the vast majority of these fragility fractures occur in osteopenic (as opposed to osteoporotic) patients poses a conflicting treatment paradigm. Thus, clinicians rely on the FRAX score to stratify in which osteopenic patients exceed the risk threshold to warrant more aggressive pharmacologic treatments.
Patients younger than 50 at increased fragility fracture risk are recommended to obtain a DXA scan if one has not been already obtained for another reason. A study from 2013 analyzed the worldwide uptake of FRAX calculation over one year from 2012 to 2013. Nearly 2.5 million calculations from 173 countries were reported, with the USA, UK, Canada, Spain, Japan, France, Belgium, Italy, Switzerland, and Turkey representing over 80% of all calculations.
Enhancing Healthcare Team Outcomes
Osteopenia and osteoporosis and its associated complications constitute a significant source of patient morbidity and mortality, and the treatment of its complications provide an enormous financial and resource burden to the healthcare system . The key is to prevent osteopenia. Thus, this is best done with an interprofessional team with a focus on patient education. All clinicians should educate patients about the morbidity of osteopenia. The nurse practitioner, pharmacist, and primary care provider should encourage the patient to eat a healthy diet rich in calcium. In addition, the patient should be encouraged to exercise, cease smoking, and abstain from alcohol. The pharmacist should educate the patient on the bisphosphonates, their benefits, and adverse effects.
All postmenopausal women should undergo bone densitometry and understand the benefits of this test.
Healthcare providers must all coordinate to ensure that patients initially diagnosed with a fragility fracture receive early follow-up with an appropriate provider experienced in managing low bone mineral density conditions. The latter has been receiving significant attention in the literature over the last few decades, as followup rates have been documented to be extremely low (i.e., in the range of 5% to 15%). The goal is to enhance interprofessional care and prevent further fracture, surgery, morbidity, and associated mortality. Evidence level: Level 2 and Level 3.