Osteoporosis: Reading Your T-score, Calculating FRAX, Which Drugs Actually Prevent Fractures, and Why Kidney Disease Changes the Rules

Why osteoporosis matters

Osteoporosis is loss of bone mass and deterioration of bone micro-architecture, making bones fragile. It is silent — the first symptom is usually a fracture. An osteoporotic fracture occurs every 3 seconds worldwide; about 1 in 3 women and 1 in 5 men over 50 will have one [1].

Hip fracture is the most serious: one-year mortality is about 20%, and around half of survivors never regain their previous mobility [1][2]. Vertebral compression fractures are often silent (height loss >3 cm, stooping, chronic back pain are clues), and the risk of a second fracture is highest in the two years after the first ("imminent risk") [2].

DXA and the T-score

Dual-energy X-ray absorptiometry (DXA) measures bone density at the lumbar spine and hip, reported as a T-score — standard deviations from the young-adult mean [1][2]:

A hip or vertebral fragility fracture means clinical osteoporosis regardless of T-score, and warrants treatment [2].

Who should have DXA [2]: women ≥65, men ≥70; postmenopausal women and men 50–69 with risk factors (prior fracture, parental hip fracture, low body weight, smoking, long-term steroids, rheumatoid arthritis, early menopause, CKD, etc.).

FRAX: 10-year fracture probability

FRAX, developed by a WHO collaborating centre, uses age, sex, BMI, fracture history, parental hip fracture, smoking, steroids, rheumatoid arthritis, secondary osteoporosis and alcohol (± femoral-neck T-score) to estimate 10-year probability of major osteoporotic and hip fracture, calibrated by country (Taiwan and Japan versions exist) [3].

Common treatment thresholds (US BHOF) [2]: 10-year hip-fracture probability ≥3% or major osteoporotic fracture ≥20%. Thresholds vary by country, and FRAX may under-estimate risk in CKD and after a recent fracture [3].

Calcium and vitamin D: practical advice

Caution: high-dose calcium supplements may raise kidney-stone and possibly cardiovascular risk (evidence inconsistent), and calcium intake in CKD must be individualised (KDIGO advises avoiding high calcium loads in adult CKD 3–5) [5].

Drugs: which actually reduce fractures?

Sequence matters: at very high risk (recent fracture, T ≤ −3.0, multiple fractures), an anabolic agent first, followed by a bisphosphonate or denosumab, outperforms the reverse order [2][6].

Kidney patients: why T-score alone is not enough

Bone disease in CKD is part of CKD-MBD (mineral and bone disorder) and includes several patterns of abnormal bone turnover — high turnover (secondary hyperparathyroidism), low turnover (adynamic bone), osteomalacia — which DXA cannot distinguish, and the wrong drug can harm (e.g. an antiresorptive in adynamic bone) [5].

Key points from the KDIGO 2017 update [5]:

1. DXA is reasonable in CKD 3a–5D with osteoporosis risk factors (reversing the 2009 advice, because DXA does predict fracture in CKD).
2. Before treatment, check PTH, alkaline phosphatase, calcium, phosphate and 25(OH)D; with very high or very low PTH, consider bone biopsy or specialist referral first.
3. eGFR ≥30 (CKD 1–3): if PTH is normal, standard osteoporosis therapy applies.
4. eGFR <30 (CKD 4–5, dialysis): bisphosphonate evidence is lacking and the drugs accumulate; denosumab is usable but hypocalcaemia risk is high; decisions should be shared between nephrology and bone specialists.
5. Controlling phosphate, PTH and vitamin D (including active vitamin D) is itself bone protection.

Transplant recipients: steroids drive bone loss (density can fall 5–10% in the first year); KDIGO suggests considering vitamin D, calcium and a bisphosphonate or denosumab in the first year if eGFR >30 and bone density is low [5].

Fall prevention: as important as medication

Fracture = fragile bone × a fall. Evidence-based measures [2][7]:

• Exercise: balance training (tai chi has the strongest evidence) and strength training ≥3 times/week.
• Medication review: hypnotics, sedatives, over-treated blood pressure (postural hypotension), polypharmacy.
• Vision: cataract surgery, correct glasses.
• Home: remove rug edges, bathroom non-slip mats and grab rails, night lights.
• Vitamin D repletion may slightly reduce falls in deficient people.
• Take particular care after dialysis when blood pressure is low and you feel weak.

When to seek care

Urgently: hip or groin pain after a fall and unable to stand; sudden severe back pain (possible vertebral fracture); a deformed wrist.

Routine appointment: height loss >3–4 cm; any low-trauma fracture after 50; long-term steroids (≥3 months); CKD with osteoporosis risk factors; menopause before 45; never had DXA and aged ≥65 (women) or ≥70 (men).

Questions to ask your doctor

1. What are my T-score and FRAX 10-year probabilities?
2. With my kidney function, which osteoporosis drug is appropriate? Should PTH be checked first?
3. Is my calcium intake adequate? Can I take calcium tablets with CKD?
4. If I start denosumab, what is the plan for stopping it later?
5. Can I join a balance/strength class?

References

1. Kanis JA, et al. European guidance for the diagnosis and management of osteoporosis in postmenopausal women (IOF/ESCEO). Osteoporos Int. 2019;30(1):3–44. https://doi.org/10.1007/s00198-018-4704-5
2. LeBoff MS, et al. The clinician's guide to prevention and treatment of osteoporosis (BHOF). Osteoporos Int. 2022;33(10):2049–2102. https://doi.org/10.1007/s00198-021-05900-y
3. Kanis JA, et al. FRAX and the assessment of fracture probability. Osteoporos Int. 2008;19(4):385–397. https://doi.org/10.1007/s00198-007-0543-5 ; FRAX tool https://frax.shef.ac.uk/
4. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. 2011. https://doi.org/10.17226/13050
5. KDIGO 2017 Clinical Practice Guideline Update for CKD-MBD. Kidney Int Suppl. 2017;7(1):1–59. https://doi.org/10.1016/j.kisu.2017.04.001
6. Camacho PM, et al. AACE/ACE Guidelines for Postmenopausal Osteoporosis—2020 Update. Endocr Pract. 2020;26(Suppl 1):1–46. https://doi.org/10.4158/GL-2020-0524SUPPL
7. Sherrington C, et al. Exercise for preventing falls in older people living in the community. Cochrane Database Syst Rev. 2019;(1):CD012424. https://doi.org/10.1002/14651858.CD012424.pub2

This article compiles publicly available medical information for educational purposes only. It is not medical advice and has not been reviewed by a practising physician. For any health or medication question, consult a qualified professional. For chest pain, sudden breathlessness, one-sided weakness or slurred speech, call your local emergency number or go to the emergency department immediately.