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Secondary Hyperparathyroidism

Normally, low blood calcium triggers an increase in parathyroid hormone (PTH) which raises the calcium level. When the calcium level goes high, the PTH is autonatically reduced which lowers the calcium level.

In Primary Hyperparathyroidism, however, this amazing feedback mechanism doesn't kick in when the PTH gets too high due to a parathyroid gland disorder and you will have high calcium and high PTH levels.

In Secondary Hyperparthyroidism, the disorder is due to an underlying condition which causes low blood calcium levels.  Here, the PTH remains high until whatever caused the low calcium in the first place has been treated. So you will have low or normal calcium and high PTH. You may also have high phosphate or low vitamin D too.

 

Causes

The low calcium levels may be caused by

  • insuffcient calcium in the diet or by  losing too much calcium in the urine. The normal level of calcium in the blood is 2.1- 2.5 mmol/L. The normal level of calcium in the urine is 2.5 to 7.5 mmol/L
  • high phosphate levels which in turn affect calcium levels may be due to diet, kidney disease, poor absorption, aluminium poisoning . Rarely this may be due to some types of cancer. The normal level of phophate in the blood is 0.8 to 1.4mmol/L.
  • low vitamin D levels due to diet, lack of sunlight, poor absorption, or problems breaking down vitamin D due to certain drugs.

 

Symptoms

Symptoms relate to the underlying causes above so may include

  • the symptoms of hypocalcaemia (low calcium)
  • the symptoms of high phosphate ( eg itching, problems with breathing, calciphylaxis or calcium deposits in the body  )
  • the symptoms of low vitamin D (eg ostoemalacia, rickets, bone deformities, joint swelling or fractures)

 

What tests do I need?

If you or your doctor suspect sceondary hyperparathyroidism, you should get the following tests  done:

  • calcium, phosphate and PTH levels. Phosphate levels will be low if you have absorption problems, and high if you have kidney failure.
  • a 24 hour urine test to determine how much calcium/phosphate is being removed from the body.
  • bone x-rays and a bone density test can help detect fractures, bone loss, and bone softening.

 

Treatment

Treating the underlying problem usually brings the calcium and PTH levels back to normal. Sometimes parathyroid surgery may be necessary. In secondary hyperparathyroidism, usually all four of the parathyroid glands are affected.

Patients with chronic kidney failure are usually given calcium and vitamin D, and are told to avoid phosphate in their diet. A medication called cinacalcet (Sensipar) may also be recommended. Sometimes, dialysis or a kidney transplant may be needed.

 

Complications

Sometimes, more often in those with kidney problems, one of the parathyroids becomes autonomous and starts producing too much parathyroid hormone after the underlying cause has been treated. You will have high calcium and high PTH. lThis, then, is called Tertiary Hyperparathyroidism. If this happens the offending parathyroid is usually removed surgically. Sometimes this may, in turn, lead to hypocalcaemia due to the long term or chronic affect on the bone.

Other complications include:

  • Increased risk of broken bones

  • Renal osteodystrophy (a condition that causes bone pain, weakness, and fractures)


   
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