Osteoporosis Blood Test: Bone Health Markers

Osteoporosis affects an estimated 3.5 million people in the United Kingdom, causing more than 500,000 fragility fractures every year. The condition is characterised by reduced bone mineral density and deterioration of bone microarchitecture, leading to bones that fracture under forces that would not normally cause injury — a stumble, a cough, or even bending to pick something up.

Women bear a disproportionate burden. After menopause, the decline in oestrogen production accelerates bone loss dramatically: women can lose up to 20% of their bone density in the 5-7 years following menopause. By the age of 80, roughly one in three women and one in five men will have sustained an osteoporotic fracture.

Can a Blood Test Diagnose Osteoporosis?

This is an important distinction to make clearly: no blood test can diagnose osteoporosis. The definitive diagnosis requires a DEXA (dual-energy X-ray absorptiometry) scan, which directly measures bone mineral density. A T-score of -2.5 or below at the hip or lumbar spine confirms osteoporosis; scores between -1.0 and -2.5 indicate osteopenia (reduced bone density that has not yet reached the osteoporotic threshold).

However, blood tests play a genuinely valuable role in osteoporosis management. They identify the nutritional deficiencies, hormonal imbalances, and metabolic conditions that drive bone loss — many of which are treatable. Correcting these underlying factors can slow or partially reverse bone deterioration, particularly when combined with appropriate medication and weight-bearing exercise.

Key Blood Markers for Bone Health

Vitamin D (25-Hydroxyvitamin D)

Vitamin D is essential for calcium absorption from the gut. Without adequate vitamin D, you absorb only 10-15% of dietary calcium, compared with 30-40% when vitamin D levels are sufficient. The body compensates for low calcium absorption by increasing parathyroid hormone (PTH) secretion, which pulls calcium from the bones to maintain blood levels — directly accelerating bone loss.

In the UK, vitamin D deficiency is endemic. Public Health England estimates that 1 in 5 adults has vitamin D levels below 25 nmol/L (the deficiency threshold). The recommended target for bone health is:

• Above 50 nmol/L: Sufficient by most guidelines
• Above 75 nmol/L: Optimal for bone health and fracture prevention, according to the Endocrine Society
• Below 25 nmol/L: Deficient — associated with osteomalacia (softening of the bones) and significantly increased fracture risk

Vitamin D testing is particularly important because supplementation doses should be guided by your actual levels. Someone at 20 nmol/L needs a loading dose (typically 50,000 IU weekly for 6-8 weeks) followed by maintenance dosing, whilst someone at 60 nmol/L may only need standard daily supplementation of 1,000-2,000 IU.

Calcium (Corrected Calcium)

Serum calcium is tightly regulated by the body, maintained within a narrow range of approximately 2.2-2.6 mmol/L. Corrected calcium adjusts for albumin levels (since roughly 40% of calcium in the blood is bound to albumin). Persistently elevated calcium (hypercalcaemia) may indicate primary hyperparathyroidism, malignancy, or excessive vitamin D supplementation. Low calcium levels can result from vitamin D deficiency, hypoparathyroidism, or chronic kidney disease.

Importantly, serum calcium is a poor indicator of bone calcium status. The body will strip calcium from bones to maintain normal blood levels, so you can have perfectly normal serum calcium whilst your bones are progressively losing mineral content. This is precisely why vitamin D and PTH are more informative markers of the underlying process.

Alkaline Phosphatase (ALP)

ALP is an enzyme found in bone, liver, and other tissues. When bone turnover is increased — as occurs in osteoporosis, Paget's disease, fracture healing, or vitamin D deficiency — bone-specific ALP rises. Elevated ALP with normal liver function tests (GGT, ALT) points toward bone as the source. In the context of osteoporosis risk assessment, an unexpectedly raised ALP may indicate accelerated bone remodelling that warrants further investigation.

Phosphate

Phosphate works alongside calcium in bone mineralisation. Low phosphate levels (hypophosphataemia) can occur in vitamin D deficiency, hyperparathyroidism, and certain rare inherited conditions. Chronically low phosphate impairs bone mineralisation, contributing to osteomalacia. Phosphate is routinely included in bone profile panels and helps complete the metabolic picture.

Parathyroid Hormone (PTH)

PTH is secreted by the four small parathyroid glands behind the thyroid. Its primary function is maintaining blood calcium levels. When calcium or vitamin D levels drop, PTH rises to compensate — a condition called secondary hyperparathyroidism. This is one of the most common and underdiagnosed drivers of bone loss.

Elevated PTH increases bone resorption (the process by which osteoclasts break down bone to release calcium into the blood). Over months and years, secondary hyperparathyroidism from untreated vitamin D deficiency causes measurable bone density loss, particularly at cortical bone sites such as the hip. Correcting vitamin D deficiency and ensuring adequate calcium intake will typically normalise PTH and reduce this source of bone loss.

Primary hyperparathyroidism — where one or more parathyroid glands are overactive independently of calcium status — is another important diagnosis that PTH testing can reveal. It affects approximately 1 in 1,000 people in the UK and is a treatable cause of osteoporosis.

Thyroid Function (TSH, Free T4)

Hyperthyroidism (overactive thyroid) accelerates bone turnover and is a recognised cause of osteoporosis. Thyroid hormones directly stimulate osteoclast activity, and even subclinical hyperthyroidism (suppressed TSH with normal free T4) has been associated with reduced bone density and increased fracture risk in several large population studies. Conversely, overtreatment of hypothyroidism with levothyroxine, resulting in a suppressed TSH, has the same bone-damaging effect. Thyroid function should be checked in anyone undergoing bone health assessment.

Oestradiol

Oestrogen is the primary hormonal protector of bone density in women. It inhibits osteoclast activity (bone resorption) and promotes osteoblast survival (bone formation). The precipitous fall in oestradiol at menopause is the single biggest driver of postmenopausal osteoporosis. Measuring oestradiol can help quantify the hormonal contribution to bone loss and inform discussions about hormone replacement therapy (HRT), which remains one of the most effective interventions for preventing postmenopausal bone loss when initiated around the time of menopause.

Additional Markers Worth Considering

• Kidney function (eGFR, creatinine): Chronic kidney disease affects vitamin D metabolism and calcium-phosphate balance, both critical for bone health
• Full blood count: To exclude conditions such as myeloma, which can present with bone pain and fractures
• Protein electrophoresis: If myeloma is suspected (particularly in older adults with unexplained back pain, anaemia, and raised calcium)
• Testosterone (in men): Hypogonadism is the male equivalent of low oestrogen as a driver of osteoporosis

Who Should Consider Bone Health Blood Tests?

• Women who are perimenopausal, menopausal, or postmenopausal
• Anyone with a family history of osteoporosis or hip fracture
• People taking long-term corticosteroids (prednisolone, dexamethasone) — even low doses increase fracture risk
• Those with coeliac disease, inflammatory bowel disease, or other malabsorption conditions
• Anyone with previous fragility fractures
• Men over 50 with risk factors (low testosterone, steroid use, low body weight)
• People with eating disorders or very low body weight

Testing With Lola Health

Our Core Health 45 blood test (£120) includes vitamin D, calcium, ALP, phosphate, thyroid function, kidney function, and a full blood count. Calcium and vitamin D are available as standard biomarkers, and additional markers such as oestradiol and PTH can be added to customise your panel for bone health assessment.

Results are reviewed by qualified clinicians and returned with detailed commentary. If your results indicate vitamin D deficiency, suboptimal calcium metabolism, or thyroid dysfunction, you will receive specific guidance on next steps — whether that involves supplementation, a GP referral for a DEXA scan, or further investigation.

Prevention Remains the Priority

Osteoporosis is often called a "silent disease" because bone loss progresses without symptoms until a fracture occurs. By the time a fracture happens, significant bone density has already been lost. Blood tests cannot replace a DEXA scan, but they identify the modifiable metabolic factors — vitamin D deficiency, secondary hyperparathyroidism, thyroid dysfunction, oestrogen decline — that accelerate bone loss. Correcting these factors is one of the most effective preventive measures available, particularly when combined with regular weight-bearing exercise, adequate dietary protein, and, where indicated, bone-protective medication.

The cost of treating an osteoporotic hip fracture in the UK exceeds £30,000, and hip fractures carry a one-year mortality rate of approximately 30% in elderly patients. Investing in a blood test to check your bone health markers is a remarkably cost-effective step toward preventing these outcomes.