Chapter 11: Getting Tested

11

Knowing your bone health status starts with the right tests. Here's what to ask for and when.

The DXA Scan: When to Get One

Standard recommendations:

Who	When to Screen
Women 65+	Routine screening recommended
Men 70+	Routine screening recommended
Postmenopausal women under 65	If risk factors present
Men 50-69	If risk factors present
Anyone with a fragility fracture	Immediately
Anyone on long-term steroids	Within first year of treatment

Risk factors that warrant earlier screening:

• Previous fracture as an adult
• Parent who broke a hip
• Low body weight (under 127 lbs / 58 kg)
• Current smoking
• Excessive alcohol (3+ drinks daily)
• Rheumatoid arthritis
• Long-term steroid use
• Early menopause (before 45)
• Conditions affecting absorption (celiac, IBD)

How often to repeat:

• Every 1-2 years if on treatment (to monitor response)
• Every 2 years for monitoring without treatment
• More frequently if rapid changes expected

Blood Tests to Request

Don't settle for just a DXA. These blood tests reveal the why behind your bone health:

Essential Tests

Vitamin D (25-hydroxyvitamin D)

• The most important blood test for bone health
• Optimal: 30-70 ng/mL
• Deficient: Below 20 ng/mL
• Many labs say "normal" starts at 20, but that's the floor, not the goal

Calcium (serum)

• Usually normal even with osteoporosis
• Abnormal levels suggest other problems (parathyroid, kidney, etc.)
• Normal range: 8.5-10.5 mg/dL

Calcium Blood Test Doesn't Show Calcium Intake

Many people assume that a "normal" blood calcium level means they're getting enough calcium. This is wrong.

Your body treats blood calcium as critical—it's essential for heart function, nerve signaling, and muscle contraction. So it maintains blood calcium within a tight range at all costs. If you're not getting enough calcium from food, your body simply pulls it from your bones (via PTH) to keep blood levels normal.

This means:

• You can have severe calcium deficiency and still show "normal" blood calcium
• You can be losing bone rapidly while blood calcium looks fine
• Blood calcium only goes abnormal when something else is wrong (parathyroid disease, kidney failure, cancer, etc.)

Bottom line: A normal serum calcium tells you your body's regulation is working—not that your calcium intake is adequate.

PTH (Parathyroid Hormone)

• Rules out hyperparathyroidism (a treatable cause of bone loss)
• Normal range: roughly 10-65 pg/mL (varies by lab)
• High PTH + high calcium = likely parathyroid problem

Bone Turnover Markers

These show how fast you're building and breaking bone:

CTX (C-terminal telopeptide) - Bone breakdown marker

• Shows how fast bone is being resorbed
• Drops significantly on anti-resorptive medications
• Must be drawn fasting, in the morning

P1NP (Procollagen type 1 N-terminal propeptide) - Bone building marker

• Shows how fast new bone is forming
• Rises on anabolic medications (teriparatide, romosozumab)

Approximate reference ranges (ng/mL—varies by lab):

Group	P1NP	CTX
Premenopausal women	15–80	0.03–0.65
Postmenopausal women	15–100	0.10–1.05
Men (adult)	15–95	0.05–0.85

These ranges are approximate. Postmenopausal women naturally have higher turnover, so values like P1NP of 80 or CTX of 0.8 can be normal. Always compare to your lab's specific reference range, and remember: the trend over time matters more than any single value.

Why Bone Markers Matter

Your doctor can use these to see if medication is working within 3-6 months—much faster than waiting for the next DXA scan. If CTX doesn't drop on a bisphosphonate, something's wrong (absorption issue? not taking correctly?).

Hormone Tests

For women:

• FSH and estradiol (confirms menopausal status if unclear)
• Consider if periods are irregular or absent

For men:

• Total testosterone (morning draw)
• SHBG (sex hormone binding globulin)
• Sensitive estradiol (LC/MS method—regular estradiol tests are inaccurate for men)
• Albumin (usually included in metabolic panel)

The Free Testosterone Testing Problem

Free testosterone is what actually matters—it's the portion available for your body to use. But here's the catch: most lab tests for "free testosterone" are notoriously inaccurate.

Why direct free testosterone tests fail: The common "analog" or "direct" assays for free testosterone can be wildly off—sometimes measuring values 5-7x lower than the true level. These tests have been criticized for decades, yet many labs still offer them.

The better approach: Calculate it. The Endocrine Society recommends calculating free testosterone from:

1. Total testosterone (measured accurately)
2. SHBG (sex hormone binding globulin)
3. Albumin

This calculation correlates much better with the gold-standard equilibrium dialysis method than direct assays do.

What is SHBG? SHBG is a protein made by your liver that binds to testosterone (and estrogen) in your blood. Testosterone bound to SHBG is "locked up" and unavailable for use. Only the unbound (free) portion can enter cells and exert effects.

SHBG Level	Effect on Free Testosterone
High SHBG	Less free testosterone available (even if total is normal)
Low SHBG	More free testosterone available

What affects SHBG:

• Increases SHBG: Aging, hyperthyroidism, liver disease, low calorie intake, estrogen therapy
• Decreases SHBG: Obesity, insulin resistance, hypothyroidism, high androgen states

Bottom line: Ask for total testosterone AND SHBG. Many online calculators (like the ISSAM calculator) can then compute your free testosterone accurately. Don't rely on a "free testosterone" direct assay.

Other Useful Tests

Complete metabolic panel - Kidney and liver function, electrolytes

CBC (Complete blood count) - Rules out blood disorders

Thyroid (TSH) - Overactive thyroid causes bone loss

Celiac panel - If any GI symptoms or unexplained bone loss

24-hour urine calcium - Shows if you're absorbing and retaining calcium properly

When to Test

Best practices:

• Vitamin D: Check at baseline, then 3 months after starting supplements, then annually
• Bone markers (CTX, P1NP): Baseline before treatment, then 3-6 months after starting medication
• Hormones: Morning draw (testosterone peaks in early morning)
• CTX: Must be fasting (eating affects results significantly)

Red Flags That Need Investigation

If you have osteoporosis, especially if you're young or male, ask about:

• Celiac disease (blood test)
• Thyroid disorders
• Hormone deficiencies
• Medication side effects (steroids, etc.)

What to Do With Results

Vitamin D low? Supplement and recheck in 3 months.

PTH high with high calcium? See an endocrinologist—possible parathyroid adenoma.

Bone markers very high? Suggests rapid turnover; treatment may be more urgent.

Testosterone low (men)? Consider TRT evaluation with a knowledgeable physician.

Celiac antibodies positive? Get endoscopy to confirm, then strict gluten-free diet.

Questions to Ask Your Doctor

1. "Can I get my vitamin D level checked?"
2. "What's my actual number?" (Don't accept just "normal")
3. "Should we check PTH to rule out parathyroid issues?"
4. "Can we do bone turnover markers to monitor treatment?"
5. "Are there any secondary causes we should test for?"

The Bottom Line

A DXA scan tells you where you are. Blood tests tell you why you're there and whether treatment is working.

Key points:

• DXA screening: 65+ for women, 70+ for men, earlier if risk factors
• Vitamin D is the most commonly deficient nutrient affecting bones
• Bone markers (CTX, P1NP) can track treatment response in months, not years
• Always look for underlying causes, especially in younger people
• Get your actual numbers, not just "normal" or "abnormal"