REMS Z-Score (Left Femur)

Lower bone density for your age can reflect a hormone disorder, an eating disorder, medication exposure, or lower bone mass built during growth. A single scan can't distinguish these possibilities or establish that you're currently losing bone.

This score comes from radiofrequency echographic multi-spectrometry, or REMS. The method uses ultrasound to estimate bone density at your left femoral neck. REMS is an emerging clinical technology with validation studies and some fracture-outcome evidence, but evidence for using this particular Z-score to predict fractures or guide treatment is limited. DXA remains the established bone density method.

What the Score Represents

The femoral neck is the narrow section of your thigh bone just below the hip joint. REMS analyzes raw ultrasound echoes from this region and compares them with reference models to estimate bone mineral density. The calculation also uses personal details such as age, sex and body size.

Bone mineral density describes the amount of mineral within a measured area of bone. DXA stands for dual-energy X-ray absorptiometry and measures this using a small dose of X-rays. REMS estimates density from ultrasound signals. Although both methods report density in the same units, their individual results aren't interchangeable.

Your Z-score expresses how far your estimated density is from the average in its age- and sex-matched reference group. Each point represents one standard deviation. A standard deviation describes the spread of values around the average; a point on this scale is not a fixed percentage of bone gained or lost.

A T-score uses a young-adult reference group. Established DXA guidance prefers Z-scores for premenopausal women and men younger than 50, while T-scores are generally used after menopause and in men aged 50 and older. These reporting conventions don't establish equivalent diagnostic performance for REMS.

Left and right hip measurements often track together, but either side can differ because of local disease, injury or loading. A left-sided result describes the scanned hip and doesn't establish that both hips have identical density.

What the Fracture Studies Show

A fragility fracture is a break caused by a fall or force that healthy bone would usually withstand. In a study enrolling about 1,500 women, REMS T-scores were associated with subsequent fragility fractures during follow-up of up to five years. Femoral neck REMS and DXA T-scores had similar fracture discrimination. This supports the technology's potential, but it doesn't directly validate a left femoral neck Z-score as a fracture-risk calculator.

REMS can also produce a separate fragility score from features of the ultrasound signal. A conference report following 533 women found that a spine fragility score distinguished future fracture cases better than spine REMS or DXA T-scores. That finding concerns a different output and skeletal site, so it can't establish the performance of this hip Z-score.

The evidence that bone screening prevents fractures comes mainly from pathways using clinical risk assessment and DXA. Trials in older women found modest reductions in hip and major osteoporotic fractures when screening was linked to appropriate care. Comparable outcome evidence hasn't established that screening younger adults with this REMS Z-score prevents fractures.

Heart Disease and Longevity

Lower bone measurements have been associated with heart disease and earlier death in observational studies. The methods matter here: hip DXA measures a different way, and heel ultrasound examines a different bone with a different technique. None of the studies below tested this REMS Z-score.

The standard deviations in these studies describe variation within their study populations. They aren't equivalent to a one-point change in your age-adjusted REMS Z-score. These associations therefore can't be translated into a personal heart-risk or lifespan estimate from this result. They also don't establish that increasing bone density prevents heart disease.

Bone Density in Specific Conditions

Small REMS studies have examined people with conditions that affect bone health. They show that the method can detect group differences, but a lower reading doesn't automatically prove greater accuracy or explain the cause:

• Anorexia nervosa: young women had lower REMS femoral neck and total hip Z-scores than healthy comparison groups. These were group comparisons, not evidence that one scan measures the rate of ongoing bone loss.
• Osteogenesis imperfecta: adults with this inherited brittle-bone disorder had differences between REMS and DXA results, including lower total hip Z-scores with REMS. Total hip measurements cover a different region from the femoral neck.
• Type 2 diabetes: a study of older women found lower REMS estimates despite relatively higher DXA density. Diabetes can increase fracture risk beyond what DXA density predicts, but disagreement between the scans doesn't establish which individual reading is correct.

Pregnancy and Your Hips

A study comparing 40 pregnant women with 60 non-pregnant women reported lower average left femoral neck REMS Z-scores in the pregnant group: about -0.08 versus 1.18. These are study averages, not diagnostic boundaries or targets.

Each woman was scanned once. The study therefore couldn't measure how much bone an individual lost during pregnancy, whether the groups differed before pregnancy, or how density changed after birth. It supports the feasibility of a radiation-free assessment, but doesn't establish that routine REMS screening during pregnancy improves outcomes.

How Close REMS Comes to DXA

Results vary substantially across studies. In a European study of about 4,300 women, femoral neck REMS identified about 90% of the cases classified as osteoporosis by DXA after scans with acquisition or analysis errors were excluded. It correctly classified about 96% of those without DXA-defined osteoporosis. Accuracy was lower when erroneous REMS acquisitions were included. These findings concern osteoporosis classification using T-scores, not the accuracy of this Z-score in younger adults.

An Australian clinical validation found that REMS and DXA measurements couldn't be used interchangeably. Other research found that demographic inputs strongly influenced REMS results. In a small experiment, changing the age or weight entered into the software changed the estimate even though the person being scanned hadn't changed. Agreement across a group doesn't guarantee agreement for an individual.

Several condition-specific studies also found important limitations:

• Lupus: one study identified only about 45% of DXA-defined osteoporosis cases with REMS. This result concerned the study's osteoporosis classification, not specifically the left hip Z-score.
• Bone loss associated with immobility: a small subgroup had only 13% agreement between REMS and DXA diagnostic categories. A reassuring REMS result may therefore be misleading in this setting.
• Older adults: in a geriatric outpatient study, femoral neck REMS identified about 46% of DXA-defined osteoporosis cases. A reassuring result couldn't reliably exclude osteoporosis.
• Peritoneal dialysis: in a longitudinal study of 20 people, DXA detected a decline in femoral neck density that REMS didn't detect, and changes measured by the two methods didn't correlate. The study didn't directly measure separate inner and outer bone compartments.

When Results Can Be Misleading

• Incorrect personal details: errors in age, sex, height or weight can affect the calculation. A real weight change can also influence the estimate through the software's reference models, as well as through biological changes in bone.
• Acquisition quality: probe placement, positioning and signal quality affect whether a scan can be interpreted reliably. Good repeatability under study conditions doesn't eliminate operator error.
• Different methods or skeletal regions: a REMS femoral neck Z-score, a DXA total hip Z-score and a REMS fragility score describe different measurements. Their changes can't be treated as equivalent.
• Conditions with limited validation: lupus, prolonged immobility and advanced kidney disease have produced inconsistent agreement with DXA in small studies.
• Assuming the lower scan is correct: arthritis and calcification can inflate some DXA measurements, especially at the spine. REMS attempts to reject interfering echoes, but a lower REMS value doesn't by itself prove that the DXA result is wrong.

Tracking Your Trend

REMS has shown good short-term repeatability. One study found about 0.32% variation when the same operator repeated hip measurements. That describes precision under the study's conditions. It doesn't establish a universal amount of change that proves bone loss, nor does it validate a small year-to-year change in Z-score.

A Z-score changes with both your estimated density and the age-matched comparison used to calculate it. A stable score can coexist with a decline in absolute density. A falling score can reflect biological loss, measurement variation or changes in the calculation's inputs. Interpretation therefore needs the underlying density measurements and scan quality, not the score alone.

Long-term monitoring with REMS is less established than monitoring with DXA. Comparisons need a consistent method, skeletal region and measurement procedure. Switching between REMS and DXA doesn't provide a valid measure of how much bone you've gained or lost.