DEXA Bone Density Test: Which Labs to Order Alongside It

What Your DEXA Score Actually Tells You (and What It Misses)

A DEXA scan measures how much mineral is packed into each square centimeter of bone at your hip and lumbar spine. The result is expressed as a T-score, which compares your density to a young adult female reference peak, and a Z-score, which compares you to women of your own age. The WHO defines osteopenia as a T-score between -1.0 and -2.5 and osteoporosis as a T-score at or below -2.5.

The scan takes about 10 minutes and uses a very low dose of ionizing radiation, roughly 1 to 10 microsieverts depending on the machine, which is far below a standard chest X-ray. What it does not tell you is whether your bone loss is driven by low estrogen, hyperparathyroidism, celiac disease, hyperthyroidism, or something else entirely. That distinction matters because the treatment for each cause is different.

T-Score Versus Z-Score: Which Number Should You Watch?

Your T-score drives treatment decisions for postmenopausal women and men over 50. Your Z-score matters more if you are premenopausal or under 50, because a Z-score at or below -2.0 signals that something beyond normal aging is accelerating bone loss and demands a secondary-cause workup. The International Society for Clinical Densitometry states that a Z-score below -2.0 in premenopausal women is "below the expected range for age" and should trigger evaluation.

How FRAX Changes the Conversation

A low-normal T-score does not automatically mean low fracture risk, and a mildly low T-score does not automatically mean high risk. The FRAX tool, validated by the WHO, integrates your BMD with clinical risk factors including age, prior fracture, parental hip fracture, smoking, alcohol, glucocorticoid use, and rheumatoid arthritis to produce a 10-year probability of major osteoporotic or hip fracture. AACE and the National Osteoporosis Foundation recommend treatment when the 10-year hip fracture probability exceeds 3% or major osteoporotic fracture probability exceeds 20% on FRAX.

How Bone Loss Differs Across Female Life Stages

Bone is not static. You reach peak bone mass between ages 25 and 30, and estrogen is the dominant protector from that point forward.

Reproductive Years (Ages 20-40)

Bone loss during this period is minimal if your cycles are regular. Hypothalamic amenorrhea, whether from low energy availability, extreme exercise, or stress, suppresses estrogen and can cause bone loss equivalent to early menopause. A landmark study in the Journal of Clinical Endocrinology and Metabolism found that recreational runners with functional hypothalamic amenorrhea had lumbar spine BMD 10 to 15% lower than eumenorrheic controls.

PCOS presents a more complicated picture. Despite often-higher androgen levels that can partially protect cortical bone, women with PCOS who have oligomenorrhea may lose trabecular bone, which is the spongy inner layer most vulnerable to fracture.

Trying to Conceive and Pregnancy

Bone density transiently drops during pregnancy and lactation as calcium is redirected to fetal skeletal development and then to breast milk. Studies show a 3 to 5% BMD decrease during lactation, with recovery generally complete within 12 to 18 months of weaning. This is why a DEXA taken while breastfeeding or immediately after weaning may underestimate your true steady-state density.

Perimenopause: The Critical Window

This is where bone loss accelerates most sharply. Estrogen withdrawal in the 2 to 3 years before the final menstrual period and the 3 years after drives losses of up to 2 to 3% per year at the lumbar spine. The Study of Women's Health Across the Nation (SWAN) documented a mean spine BMD loss of 10.6% over the menopausal transition. A woman who enters perimenopause with a T-score of -1.0 can cross the osteoporosis threshold within 5 to 7 years without intervention.

Postmenopause

Bone loss slows after the first 5 years but continues. By age 80, a woman may have lost 30 to 40% of peak trabecular bone. USPSTF recommends screening DEXA for all women 65 and older and for younger postmenopausal women whose 10-year fracture risk equals or exceeds that of a 65-year-old white woman with no additional risk factors.

The 8 Paired Labs That Complete Your DEXA Picture

A DEXA scan in isolation is an incomplete clinical assessment. Below is the WomanRx Bone Workup Framework: 8 paired tests grouped by what they rule in or out, with the specific question each answers.

Group 1: Secondary-Cause Screening (Rule Out Treatable Causes)

These tests are standard of care before attributing low BMD to menopause or aging alone. AACE's 2020 Clinical Practice Guidelines on the Diagnosis and Treatment of Postmenopausal Osteoporosis list all five as part of the recommended laboratory evaluation for secondary causes.

1. 25-hydroxyvitamin D (25-OH D)

Target: 30 to 50 ng/mL for bone health. Deficiency is the most correctable driver of low BMD and also suppresses calcium absorption. A meta-analysis in the Journal of Bone and Mineral Research found that vitamin D supplementation in women with baseline levels below 20 ng/mL reduced hip fracture risk by 18%. Draw fasting or non-fasting; time of year matters since levels drop in winter.

2. Calcium (total serum) and albumin, or ionized calcium

Hypercalcemia points toward primary hyperparathyroidism or malignancy. Hypocalcemia suggests malabsorption or vitamin D deficiency. Always check albumin alongside total calcium, because low albumin falsely lowers the reported total calcium value.

3. Parathyroid hormone (PTH, intact)

Elevated PTH with normal or high calcium means primary hyperparathyroidism, a cause of bone loss that is surgically correctable. Elevated PTH with low calcium means secondary hyperparathyroidism, most often from vitamin D deficiency or kidney disease. Primary hyperparathyroidism accounts for up to 15 to 20% of secondary osteoporosis cases identified during workup.

4. Thyroid-stimulating hormone (TSH)

Both overt and subclinical hyperthyroidism accelerate bone remodeling and increase fracture risk. Women on thyroid hormone replacement who are over-suppressed (TSH <0.1 mIU/L) lose bone at a measurable rate. A 2015 meta-analysis in the Journal of Bone and Mineral Research confirmed that long-term levothyroxine at suppressive doses reduces BMD at the hip and spine in postmenopausal women.

5. Complete metabolic panel (CMP) including creatinine and liver enzymes

Chronic kidney disease reduces 1-alpha hydroxylase activity, impairing vitamin D activation. Liver disease impairs 25-hydroxylation of vitamin D. Both show up as abnormalities in the CMP before symptoms appear.

Group 2: Bone Turnover Markers (Is Bone Loss Active Right Now?)

DEXA reflects cumulative density at one point in time. Bone turnover markers tell you the current pace of remodeling, which is essential for monitoring treatment response.

6. CTX (C-telopeptide of type I collagen, serum)

CTX is a resorption marker. High CTX means bone is breaking down faster than it is being built. CTX drops within 3 to 6 months of starting antiresorptive therapy (bisphosphonates, denosumab), making it the preferred early efficacy monitor. Draw fasting in the morning, because CTX has a diurnal variation and is suppressed by food. The International Osteoporosis Foundation recommends drawing CTX fasting before 10 a.m. For reproducible results.

7. P1NP (procollagen type I N-terminal propeptide, serum)

P1NP is a bone formation marker. Anabolic therapies like teriparatide or romosozumab raise P1NP within weeks, which is why it is the preferred marker when monitoring these agents. P1NP does not have the same food or time-of-day sensitivity as CTX, giving it a practical advantage in clinical settings.

Group 3: Hormone Status (Estrogen and the Reproductive Context)

8. Estradiol (E2) and FSH

Estradiol is the primary estrogen protecting bone. FSH rises as ovarian reserve declines in perimenopause. A single day-3 FSH above 10 to 15 IU/L in a woman under 40 may indicate diminished ovarian reserve; FSH above 40 IU/L paired with amenorrhea for 12 months confirms menopause. These values contextualize a low T-score: a perimenopausal woman with E2 below 30 pg/mL is losing bone faster than her DEXA alone reveals.

For women in reproductive years with irregular cycles or suspected hypothalamic amenorrhea, add a prolactin and LH to the hormone panel to distinguish the cause.

Additional Tests for Specific Clinical Situations

Not every woman needs this extended panel, but certain presentations demand it.

Celiac Disease Screen (tTG-IgA with total IgA)

Celiac disease causes malabsorption of calcium and vitamin D and is underdiagnosed in women. Prevalence in women is roughly 1.5 times higher than in men, and up to 40% of adults with celiac disease present with low BMD as their first notable finding. Order this if your patient has unexplained low Z-score, IBS-like symptoms, iron-deficiency anemia, or a first-degree relative with celiac disease.

24-Hour Urine Calcium and Creatinine

Hypercalciuria (urine calcium above 250 mg/24 hours in women) drives bone loss by forcing the kidneys to pull calcium from the skeleton to maintain serum levels. Thiazide diuretics reduce urinary calcium loss and are sometimes used specifically for this indication.

DHEA-S and Free Testosterone

In postmenopausal women, adrenal androgens partially convert to estrogens in peripheral fat tissue. Very low DHEA-S may contribute to accelerated bone loss after menopause, though the therapeutic evidence for DHEA supplementation on fracture outcomes remains limited. Draw these if the clinical picture suggests adrenal insufficiency or if the woman has had bilateral oophorectomy.

Serum Protein Electrophoresis (SPEP)

Multiple myeloma can present as vertebral compression fractures with low BMD on DEXA. SPEP is appropriate in older women with unexpectedly severe bone loss, anemia, or back pain, particularly if the DEXA shows disproportionate spine loss relative to hip.

Reading Your Results: What the Numbers Mean for You

Normal Range

A T-score at or above -1.0 is considered normal by WHO criteria. A Z-score at or above -2.0 is within the expected range for premenopausal women. The International Society for Clinical Densitometry emphasizes that "normal" on DEXA does not mean zero fracture risk, because most osteoporotic fractures occur in women with T-scores in the osteopenic range due to the much larger number of women in that category.

Low Bone Density: What It Means and What Moves the Number

Low BMD (T-score below -1.0) means your bone mineral content is lower than the young adult female reference. The clinical question is not just how low but why. A 48-year-old perimenopausal woman with T-score -1.8 and estradiol of 18 pg/mL has a very different treatment pathway from a 48-year-old with T-score -1.8 and primary hyperparathyroidism.

Interventions that raise BMD, in rough order of effect size:

• Anabolic therapy (teriparatide, romosozumab): gains of 9 to 13% at spine over 12 to 24 months
• Menopausal hormone therapy (MHT): the Women's Health Initiative showed a 3.7% increase in hip BMD and 4.5% at the spine over 3 years in women using conjugated equine estrogen
• Bisphosphonates (alendronate, zoledronate): 5 to 8% spine gain over 3 years
• Denosumab: approximately 6 to 9% spine gain over 3 years
• Calcium and vitamin D (correction of deficiency): modest but foundational, typically 1 to 2% gain

Weight-bearing and resistance exercise preserves BMD but rarely reverses established osteoporosis on its own. Every 10% increase in lean muscle mass is associated with a statistically significant improvement in BMD, but exercise alone is not a substitute for pharmacotherapy in women with T-scores below -2.5 or prior fragility fracture.

High Bone Density

A T-score above +1.0 to +2.0 is unusual but not inherently pathological. Very high BMD can be a normal familial variant, a reflection of high body weight (mechanical loading increases BMD), or, rarely, a sign of conditions such as osteopetrosis or Paget disease of bone. High BMD on DEXA does not eliminate all fracture risk, particularly if bone quality is poor.

Who Should Get a DEXA and When: A Life-Stage Guide

Ages 20-39: DEXA is not routine. Consider if: amenorrhea lasting more than 6 months, eating disorder history, glucocorticoid use exceeding 5 mg prednisone daily for more than 3 months, or premature ovarian insufficiency (POI) diagnosed before age 40.

Ages 40-49 (perimenopause likely): DEXA is appropriate if FRAX risk is elevated, if she has a fragility fracture, or if she is starting or considering discontinuing menopausal hormone therapy and baseline BMD will guide that decision.

Ages 50-64: Screen if postmenopausal with any clinical risk factor. USPSTF gives a Grade B recommendation to screening all women 65 and older, and a recommendation to screen younger postmenopausal women with elevated FRAX risk.

Ages 65 and older: Universal screening recommended.

Premature ovarian insufficiency (POI): Any woman diagnosed with POI before age 40 should have a baseline DEXA at diagnosis and repeat every 1 to 2 years, because the cumulative estrogen deficit is severe and begins decades earlier than typical menopause.

Pregnancy, Lactation, and Contraception Considerations

DEXA uses ionizing radiation. The dose per scan is very low (1 to 10 microsieverts, comparable to a transatlantic flight), but no ionizing radiation is considered zero risk in pregnancy. Accordingly, DEXA should be deferred until after delivery and, where possible, after weaning.

If a pregnant woman suffers a fragility fracture and imaging is genuinely necessary, MRI without gadolinium is preferred for vertebral assessment. Plain radiographs can be used with abdominal shielding if absolutely required.

Transient pregnancy-associated osteoporosis (PAO) is rare but real, typically presenting with vertebral or hip fractures in the third trimester or postpartum period. Case series estimate PAO affects roughly 0.4 per 100,000 pregnancies, and it resolves spontaneously in most cases within 12 to 18 months of weaning. DEXA obtained during or immediately after lactation will underestimate true steady-state BMD and should be repeated 12 months after weaning before making treatment decisions.

For women of reproductive age started on bisphosphonates: bisphosphonates incorporate into bone and have a long skeletal half-life, raising theoretical fetal skeletal concerns if pregnancy occurs during or after therapy. The FDA classifies alendronate as Pregnancy Category C based on animal data; human pregnancy data are limited but do not show a clearly elevated malformation rate. Prescribing bisphosphonates to premenopausal women who may become pregnant requires a specific conversation about reproductive plans and a reliable contraceptive strategy during treatment. Denosumab carries a stronger fetal risk signal and is generally avoided entirely in premenopausal women who are not using highly effective contraception.

Who This Is Right For and Who Should Wait

Strong indication for full DEXA plus paired labs:

• Postmenopausal women (any age) with one or more risk factors (fracture after age 40, parental hip fracture, smoking, alcohol, low body weight, glucocorticoid use)
• All women 65 and older
• Women with POI, hypothalamic amenorrhea, or eating disorder history
• Women with PCOS and oligomenorrhea who have been anovulatory for years
• Women starting or stopping menopausal hormone therapy
• Women on chronic glucocorticoids, aromatase inhibitors, GnRH agonists, or antiepileptics (enzyme-inducing types)
• Women with unexplained fracture at any age

Situations where DEXA should be deferred or interpreted with caution:

• Active pregnancy
• Within 6 to 12 months of weaning (BMD may be transiently suppressed)
• Severe scoliosis or vertebral compression fractures causing artifactually high lumbar spine T-scores (in these cases, hip is the more reliable measurement site)
• Recent barium studies or nuclear medicine scans (wait 7 to 10 days to avoid interference)

Monitoring: How Often to Repeat DEXA

Once you have a baseline and a treatment or monitoring plan, the repeat interval depends on clinical context. The Endocrine Society's 2019 guideline on pharmacological management of osteoporosis recommends repeat DEXA every 1 to 2 years during pharmacological treatment and every 2 to 5 years in lower-risk women not on therapy. Bone turnover markers (CTX and P1NP) can be checked at 3 to 6 months after starting therapy to confirm the expected response before the next DEXA date.

"A DEXA without a paired secondary-cause workup is like a blood pressure reading without knowing whether the patient is on stimulants. The number tells you something, but you don't know what you're treating." This reflects a clinical principle consistently applied at WomanRx: the DEXA is the starting point, not the conclusion.