Bone density scans (Dexa)

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Contents and links: What is a DEXA scan | Who needs one | Having a DEXA scan | DEXA scores | Issues with bisphosphonates | Look after your bones | Lifestyle and aromatase inhibitors | Lifestyle after cancer |  
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What is a DEXA scan A DEXA scan measures the density of calcium in the bones. This steadily decreases as we get older but if it becomes impaired (osteopenia) or there is significant loss (osteoporosis) the may be a risk of fracture. There are now lifestyle and medical interventions which can treat bone loss so it is important to detect this early with a DEXA scan. The recommendations on this page are kindly supplied by the West Anglia Cancer Network and are a guideline to standard practice - They are likely to differ from hospital to hospital or between individual oncologist and the circumstances of individual patients but are illustrated here as an example of typical recommendations for patients taking aromatase inhibitor drugs in the UK. All patients taking aromatase inhibitors should be given lifestyle advice on exercise, smoking and diet.  

Who needs a DEXA scan

  • Post menopausal taking an Aromatase Inhibitor (anastrazole, letrozole, exemestane).
  • Postmenopausal women who have received chemotherapy not on tamoxifen.
  • Pre-menopausal women who are taking tamoxifen.
  • Premature menopause (<45 years)

  • Premature menopause induced by Zoladex, chemotherapy or oophorectomy.

  • Long term steroids, hypothyroidism, chronic renal failure.

  • Men taking long term Zoladex (angrogen deprevatin)

  • Family history of osteoporosis

  • Long term sedentary lifestyle 

Having a DEXA scan  

A DEXA scan is a painless test that measures the density of bones. DEXA stands for dual energy x-rays absorptiometry. There are two different types of DEXA scanning devices, central and peripheral. Central DEXA devices are large machines that can measure bone density in the centre of your skeleton, such as your hip and spine. Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of your skeleton, such as your wrist, heel or finger.

During a DEXA scan, you will be asked to lie on your back on a couch and to keep still while the scan is being taken. The scan usually takes between 10 and 20 minutes, depending on which part of your body is being examined, and whether a central or peripheral scanner is being used. There are no injections.

In order to check for osteoporosis, the doctor commonly scans the lower back bones (vertebrae) and hips. The forearm may also be scanned, because it has a different level of calcium content from other body parts.

No preparation for the test is required and, depending on which part of your body is being scanned, you may be able to remain fully dressed, in clothes without metal fastenings. It is a painless procedure and you can go straight home afterwards.

The information from the scanner is sent to a computer which calculates a score for the density of your bone. A low score indicates that the bone is less dense than it should be, and is more likely to break. If a DEXA scan shows that you have osteoporosis, you may be given advice and treatment to help strengthen your bones.

The bone density scores

Most scans produce a T score and a Z score referring to the bone density in a number of areas of the body. Usually this includes the spine and hips but can often include the wrist and ankle. A T score of zero is normal. Less than zero means the bone density is impaired and your bone density may need some lifestyle or medical attention. The table below gives an example of management recommendations for varying T-scores. The Z score is basically a T score but adjusted to the age at the time of the scan

 

The management and rescanning interval is determined by the T-score:

T score > -1

T score  1 to 2.5

T score less than 2.5

Dietary screen

Lifestyle advice

Lifestyle advice

Lifestyle advice

 

Calcium and vitamin D 

Bisphosphonate with calcium & vit D for 5 yrs.

Rescan at 18 months if taking an AI, 3 years on Tamoxifen

Rescan at 1 year

Rescan at 3-5 years

  * Z score (age adjusted) if < -2 refer patient to endocrine physician to investigate for endocrine abnormalities.

Other issues with bisphosphonates

Bisphosphonate prescribing; eg Risedronate 35mg or Aledronate 70mg PO once weekly. Always prescribe a calcium/vitamin D supplement such as Adacal-D

Weekly bisphosphonate dosing is effective, better tolerated than daily (avoids daily insult to oesophagus) with better compliance.

Dosing instructions are critical and should be reinforced at follow-up visit: take first thing in the morning, follow by drink of water, sit upright for 30 minutes, do not take lying down and do not eat or drink for 30 minutes after taking the tablet.

DEXA response to bisphosphonates is virtually universal (failure of response is a sign of non-compliance), so no need to rescan until end of five year course (more valuable to spend time ensuring compliance at each follow up visit).

Bisphosphonates are absolutely contraindicated in pregnancy so make sure younger patients are aware of this and taking appropriate precautions, even if apparently menopausal. A 6 month washout period is needed after risedronate if attempting to conceive (which is the same as the recommended tamoxifen washout period).

Patients who cannot tolerate oral bisphosphonates and have T scores less than -2.5 should be given monthly pamidronate infusions for five years.  Other intravenous preparations as they become licensed may become preferable.

Patients who have moderate to severe renal failure should only take Bonefos only under strict supervision. Care should be taken with Bonefos if it is taken with non-steroidal anti-inflammatory drugs.

Patients who have moderate to severe renal failure should only take Bonefos only under strict supervision. Care should be taken with Bonefos if it is taken with non-steroidal anti-inflammatory drugs.

 

Lifestyle guidelines to minimise bone loss:

Increase  calcium vitamin D in the diet 
Peat protein mainly from  pulses/soya rather than meat
Regular physical activity
Stop smoking
Avoid excessive alcohol intake
Avoid excessive caffeine intake (>4 cups/day)

Underweight (<18.5kg/m2)

 


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