Blood Tests for Osteoporosis and Bone Health
No blood test diagnoses osteoporosis. Here is the Australian screen your GP uses to find the treatable causes behind a low bone density result, and why vitamin D and calcium are corrected before treatment starts.
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· · Reviewed against the sources listed at the end of this page.
The Quick Answer
No blood test diagnoses osteoporosis. The diagnosis is made on a DEXA (dual energy X-ray absorptiometry) bone density scan. The scan measures how dense your bone is at the hip and spine and expresses the result as a T-score, compared with a healthy young adult average. A T-score of -2.5 or below at the hip or spine meets the definition of osteoporosis. A T-score between -1.0 and -2.5 is called osteopenia, or low bone mass.
Blood tests are ordered for a different reason: to find a treatable secondary cause sitting behind a low bone density result. Vitamin D deficiency, an overactive parathyroid gland, thyroid disease, coeliac disease and low testosterone in men are all common, correctable contributors that a DEXA scan cannot detect on its own. A secondary cause is found in a meaningful minority of people investigated for osteoporosis, more often in men and in younger women than in older postmenopausal women, and finding one changes the treatment plan.
The practical difference: the scan and the blood screen answer two different questions. The DEXA scan tells you how dense your bone is and how urgently it needs treating. The blood tests tell you why it may have become that way, and whether anything needs fixing before, or instead of, starting bone-specific medication.
The Standard Secondary Cause Screen
This is the panel ordered when someone is diagnosed with, or is being investigated for, low bone density. Every Australian pathology provider sets its own exact reference interval, so always check the range printed on your own report rather than the typical figures below.
Corrected calcium
Total calcium adjusted for your albumin level. Both a high and a low result need explaining before any bone medication is started.
Phosphate
Read alongside calcium and PTH. Low phosphate with high calcium and high PTH supports primary hyperparathyroidism.
Magnesium
Low magnesium blunts the parathyroid response and can stop vitamin D and calcium replacement from working properly.
Alkaline phosphatase (ALP)
A marker of bone and liver activity together. An isolated rise with normal liver enzymes points to a bone source, such as Paget disease or a healing fracture.
25-hydroxyvitamin D
The most common reversible finding on this screen. Deficiency drives secondary hyperparathyroidism and directly weakens bone.
Parathyroid hormone (PTH)
Only interpretable alongside calcium and vitamin D from the same sample, never read on its own.
Kidney function (UEC, eGFR)
Determines whether bisphosphonates can be used safely and whether denosumab needs closer calcium monitoring.
Liver function tests (LFTs)
Excludes chronic liver disease and confirms whether a raised ALP is coming from bone or liver.
Full blood count (FBC)
Unexplained anaemia, alongside bone pain or a raised ESR, is one of the earliest clues to myeloma.
ESR or CRP
A raised inflammatory marker without an obvious infection is one of the triggers for a myeloma screen.
Thyroid function (TSH)
Untreated hyperthyroidism, or a thyroxine dose that runs too high, both accelerate bone turnover.
Coeliac serology (anti-tTG IgA)
Undiagnosed coeliac disease causes malabsorption of both calcium and vitamin D from the gut.
Morning testosterone (men only)
Low testosterone is a significant and frequently missed reversible cause of osteoporosis in men.
Interpreting the Patterns
No single result on this screen is read alone. The combination of PTH, calcium and vitamin D in particular tells a specific story, and the pattern is what determines what happens next.
High PTH + Low Vitamin D + Normal or Low Calcium
By far the most common pattern found on this screen. Vitamin D deficiency reduces calcium absorption from the gut, so the parathyroid glands raise PTH to pull calcium out of bone instead, keeping blood calcium normal at the bone's expense.
Common causes: Vitamin D deficiency, low dietary calcium intake, malabsorption including undiagnosed coeliac disease. Usually corrects with vitamin D and calcium replacement over weeks to months.
High PTH + High Calcium
The parathyroid glands are producing PTH independently of what the body needs, driving both PTH and calcium up together. This is a distinct condition from vitamin D deficiency and does not correct with vitamin D replacement alone.
Common causes: A single parathyroid adenoma in most cases. Confirmed with a 24-hour urine calcium and often referred to an endocrine surgeon.
Low or Undetectable PTH + High Calcium
The parathyroid glands have appropriately switched off, but calcium is still high, meaning something else is driving it. This pattern needs prompt investigation rather than routine follow-up.
Common causes: Malignancy including myeloma, excess vitamin D intake, sarcoidosis, or prolonged immobility. Serum protein electrophoresis and free light chains are usually added straight away.
High ALP Alone, With Normal Calcium, Phosphate and Liver Enzymes
Because ALP comes from both bone and liver, a normal set of liver enzymes confirms the rise is coming from bone activity rather than the liver.
Common causes: Paget disease of bone, a recent or healing fracture, or bone metastases. Usually prompts an X-ray of the affected area.
Low TSH, or a Thyroxine Dose Running High
Excess thyroid hormone, whether from an overactive thyroid or a thyroxine replacement dose that has crept too high, speeds up the entire bone remodelling cycle and accelerates bone loss over time.
Common causes: Hyperthyroidism such as Graves disease or a toxic nodule, or over-replacement in someone already taking thyroxine. Usually corrected by adjusting thyroid treatment.
Low Morning Testosterone (Men)
Testosterone helps maintain bone density in men. A genuinely low result on a fasting, before 10am sample is a significant and treatable contributor to male osteoporosis.
Common causes: Primary testicular failure, pituitary disease, opioid use, or late-onset hypogonadism with ageing. Usually referred for an endocrinology assessment before testosterone replacement is considered.
Raised ESR or CRP, With Anaemia or Renal Impairment
This combination, alongside unexplained low bone density or a fragility fracture, is the classic trigger to look specifically for multiple myeloma before assuming the cause is purely age-related.
Common causes: Multiple myeloma. Investigated with serum protein electrophoresis, serum free light chains, and sometimes a skeletal survey or a haematology referral.
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Upload Your Blood Test ResultsWhen the First-Line Screen Points Somewhere Specific
These second-line tests are not ordered as a matter of routine. Each one is added only when a specific abnormality on the first-line screen, or a specific clinical feature, points toward it.
Serum protein electrophoresis (SPE) and serum free light chains
Ordered when: Unexplained anaemia, a raised ESR, renal impairment, or hypercalcaemia not explained by PTH
Screens for multiple myeloma, a cause of bone loss and fracture that mimics osteoporosis on a DEXA scan but needs entirely different treatment.
24-hour urine calcium
Ordered when: High PTH together with high calcium
Distinguishes true primary hyperparathyroidism from familial hypocalciuric hypercalcaemia, a benign genetic condition that does not need surgery.
Cortisol screening (overnight dexamethasone suppression test or 24-hour urinary free cortisol)
Ordered when: Clinical features suggesting Cushing syndrome, such as easy bruising, muscle weakness or a rounded face, alongside an otherwise unexplained fracture
Excess cortisol causes rapid bone loss and is often under-recognised.
Serum tryptase
Ordered when: Unexplained fractures with flushing, itching, or a history of skin lesions such as urticaria pigmentosa
Screens for systemic mastocytosis, a rare but genuine cause of unexplained osteoporosis and fracture.
Iron studies
Ordered when: Anaemia on the full blood count, or coeliac serology suggesting malabsorption
Confirms whether iron deficiency is part of the same malabsorption process affecting calcium and vitamin D.
Bone Turnover Markers: CTX and P1NP
CTX (C-terminal telopeptide, sometimes written beta-CTX) measures how quickly bone is being broken down. P1NP (procollagen type 1 N-terminal propeptide) measures how quickly new bone is being formed. Together they are called bone turnover markers.
Neither test diagnoses osteoporosis, and neither is used to decide whether you have low bone density: both overlap too widely between people with normal and low bone density to be useful for diagnosis. They are used to monitor how well treatment is working once it has started.
Once a bisphosphonate is started, CTX typically falls by 50 to 70 per cent within three months if the medication is being taken correctly and absorbed as intended. A P1NP that has barely moved at three to six months is one of the more reliable early clues that a tablet is not being taken as directed. The usual reason is the strict empty-stomach dosing bisphosphonates require, and it shows up well before the next DEXA scan would.
Both markers have significant day-to-day and time-of-day variation, so they are best measured fasting, in the morning, and ideally on the same instrument each time if you are having them repeated.
Symptoms of a Fragility Fracture, and When to Seek Urgent Care
Osteoporosis itself causes no symptoms. The first sign is often a fragility fracture: a broken bone from a fall from standing height or less, or, in the spine, sometimes with no clear injury at all.
Before Starting Treatment: Correcting Vitamin D and Calcium First
Bisphosphonates, such as alendronate, risedronate and zoledronic acid, and denosumab both work by slowing the cells that break down bone. If either is started while vitamin D is deficient or corrected calcium is low, the drug can suppress bone turnover so effectively that blood calcium falls further, sometimes to a dangerously low level. This is called treatment-induced hypocalcaemia, and it is preventable.
Your GP follows a practical rule: correct vitamin D deficiency, and calcium if it is low, recheck both, and only then start the bisphosphonate or denosumab. This typically adds a matter of weeks, not months, to the timeline, and is not a reason to delay the DEXA scan or the rest of the workup.
Kidney function also determines which medication is appropriate. Oral and intravenous bisphosphonates are cleared by the kidneys and are generally avoided, or used at a reduced dose with specialist input, below an eGFR of approximately 30 to 35 mL/min/1.73m2. Denosumab is not cleared renally and can be used at a lower eGFR, but the hypocalcaemia risk is significantly higher in kidney impairment, so calcium is checked more frequently, sometimes within the first two weeks of the first dose, in anyone with reduced kidney function.
Medicare Rules for DEXA Scans
Medicare Benefits Schedule rules for bone density scans depend on your age and, if you are under 70, on having a qualifying risk factor.
Aged 70 or over
An initial DEXA scan is Medicare rebated without needing any specific risk factor.
Under 70, with a qualifying risk factor
Includes a previous minimal trauma fracture, prolonged corticosteroid use of around three months or more, a condition known to cause bone loss such as hyperparathyroidism or coeliac disease, early menopause, or male hypogonadism.
Monitoring known osteoporosis
Repeat scans are generally rebated at a minimum two-year interval, though some high-risk situations, such as long-term high-dose corticosteroid therapy, allow more frequent monitoring.
Scan requested outside these criteria
Still available privately, typically around 100 to 150 dollars at most Australian radiology and pathology providers.
Your GP or the radiology provider can confirm your specific eligibility before the scan is booked, since rebate rules are periodically updated.
What Your GP Will Do Next
Confirm the diagnosis with a DEXA scan
If a DEXA scan has not already been done, this comes first. Blood tests alone never confirm osteoporosis, and the T-score also determines how urgently treatment is needed.
Review every result in the secondary cause screen
Even one abnormal result, such as a low vitamin D or a mildly raised PTH, changes the plan, because a treatable cause found now can reduce or remove the need for lifelong bone medication.
Treat any correctable cause first
Vitamin D and calcium replacement, thyroid dose adjustment, a gluten-free diet for coeliac disease, or endocrine surgery for primary hyperparathyroidism are all addressed before or alongside starting bone-specific treatment.
Correct vitamin D and calcium before starting a bisphosphonate or denosumab
This is done routinely, not just when levels are severely abnormal, because both drug classes can trigger significant hypocalcaemia in someone who starts treatment already deficient.
Choose a treatment based on kidney function and preference
Oral or intravenous bisphosphonates are generally avoided, or dose-adjusted with specialist input, below an eGFR of approximately 30 to 35 mL/min/1.73m2. Denosumab can be used at lower eGFR but requires closer calcium monitoring, since hypocalcaemia risk is higher in kidney impairment.
Arrange a falls-risk assessment and lifestyle review
Vision, medication review, home hazards, weight-bearing exercise, adequate dietary calcium, smoking cessation and limiting alcohol are all addressed alongside any medication, since preventing the fall matters as much as strengthening the bone.
Set a monitoring plan
A repeat DEXA scan is typically arranged in one to two years. If a bisphosphonate is started, CTX or P1NP at three to six months confirms the medication is being taken correctly and is working, well before the next scan is due.
Sources and reference ranges
Adult reference ranges on this page follow the AACB and RCPA harmonised reference intervals unless stated otherwise; the range printed on your own report always takes precedence because laboratories differ.
Blood Tests for Osteoporosis and Bone Health: Frequently Asked Questions
Does a blood test diagnose osteoporosis?
No blood test diagnoses osteoporosis. The diagnosis is made on a DEXA (dual energy X-ray absorptiometry) bone density scan, which measures how dense your bone is at the hip and spine and compares the result to a healthy young adult average, expressed as a T-score. A T-score of -2.5 or below at the hip or spine meets the definition of osteoporosis. Blood tests are ordered for a different reason: to look for a treatable secondary cause, such as vitamin D deficiency, an overactive parathyroid gland, thyroid disease, or low testosterone, that may be contributing to low bone density alongside age and menopause.
What blood tests are done for osteoporosis?
The standard secondary cause screen includes corrected calcium, phosphate, magnesium, alkaline phosphatase, 25-hydroxyvitamin D, parathyroid hormone (PTH), kidney function (UEC and eGFR), liver function tests, a full blood count, ESR or CRP, thyroid function (TSH), and coeliac serology. In men, a morning testosterone level is also checked, since low testosterone is a common and often overlooked reversible cause of male osteoporosis. If any of these come back abnormal, more specific second-line tests are added depending on the pattern found.
Why do I need a vitamin D and calcium test before starting a bisphosphonate or denosumab?
Bisphosphonates and denosumab both work by slowing the cells that break down bone. If you start either medication while vitamin D deficient or with a low corrected calcium, the drug can suppress bone turnover so effectively that your blood calcium drops further, sometimes to a dangerously low level. This is called treatment-induced hypocalcaemia and can cause muscle cramps, tingling and, in severe cases, seizures. Correcting vitamin D and calcium beforehand, and rechecking them, is a standard safety step before either medication is started.
What is a secondary cause of osteoporosis?
A secondary cause is an identifiable medical condition contributing to low bone density, rather than bone loss simply from ageing and menopause. Common examples include vitamin D deficiency, primary hyperparathyroidism, hyperthyroidism or thyroxine over-replacement, coeliac disease, chronic kidney or liver disease, long-term corticosteroid use, and low testosterone in men. A secondary cause is found in a meaningful minority of people investigated for osteoporosis, more often in men and younger women, and finding one matters because it is frequently directly treatable.
Do CTX and P1NP diagnose osteoporosis?
No. CTX, a marker of bone breakdown, and P1NP, a marker of new bone formation, are bone turnover markers, not diagnostic tests. They cannot tell you whether you have osteoporosis, because levels overlap too widely between people with normal and low bone density. Their real value is in monitoring treatment: a significant fall in CTX or P1NP within three to six months of starting a bisphosphonate confirms the medication is being taken correctly and is working, which matters because oral bisphosphonates have strict dosing requirements that are easy to get wrong.
Is a DEXA bone density scan covered by Medicare?
Yes, in most circumstances. Anyone aged 70 or over can have an initial DEXA scan rebated by Medicare without needing a specific risk factor. Under 70, you generally need a qualifying reason, such as a previous minimal trauma fracture, prolonged corticosteroid use, a condition known to cause bone loss such as hyperparathyroidism or coeliac disease, or early menopause. Repeat scans to monitor known osteoporosis are usually rebated at a minimum two-year interval, sometimes more often in specific high-risk situations. Your GP can confirm your eligibility when requesting the scan.
Can my osteoporosis blood tests all come back normal?
Yes, and this is the most common outcome, especially in older postmenopausal women, where osteoporosis is often simply the result of age-related and post-menopausal bone loss with no single reversible cause behind it. A completely normal secondary cause screen does not mean the blood tests were pointless. It rules out the treatable explanations and confirms that starting bone-specific treatment, if your DEXA result and fracture risk warrant it, is the right next step without further delay looking for a hidden cause.
What does high parathyroid hormone with low vitamin D mean?
This is the single most common abnormal pattern found on an osteoporosis blood screen, called secondary hyperparathyroidism. When vitamin D is low, your gut absorbs less calcium from food, so your parathyroid glands release more PTH to pull calcium out of your bones instead, keeping blood calcium normal at the expense of bone density. It is usually corrected simply by replacing vitamin D, after which PTH falls back toward normal over some weeks to months. It differs from primary hyperparathyroidism, where PTH and calcium are both raised together.
Do men need different blood tests for osteoporosis?
The core secondary cause screen is the same for men and women, with one addition for men: a morning, before 10am, total testosterone level. Low testosterone, or hypogonadism, is found in a meaningful proportion of men investigated for osteoporosis and is a significant, reversible contributor to bone loss when present. Because osteoporosis in men is less common overall and more often has an identifiable secondary cause than in postmenopausal women, completing the whole screen matters in male osteoporosis.
Related Reading
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Upload your pathology PDF and SmarterBlood's AI will explain your calcium, vitamin D, PTH and every other marker in plain English, flag which pattern above matches your own results, and track your bone and mineral panel over time with Australian reference ranges.
This page provides general educational information about the blood tests used to investigate osteoporosis and bone health. It is not a substitute for professional medical advice, diagnosis, or treatment, and does not diagnose osteoporosis, which requires a DEXA bone density scan. Always discuss your results with your GP, who has access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.