Patient information from Canterbury Health Limited Endocrine Services
LOW BLOOD CALCIUM LEVELS ("HYPOCALCAEMIA")
What is hypocalcaemia and why is it important?
Hypocalcaemia means an abnormally low level of calcium in the blood stream. Normally
the body is able to keep the blood level within a narrow range (2.2-2.6 mmol/L) which in
health fluctuates little in any one person.
If for some reason the calcium level falls well below normal, important symptoms can
occur. For instance, muscles tighten up (especially if under repetitive strain), and painful
muscle cramps and "pins and needle" sensations may develop.
These symptoms are more likely to occur if there is a sudden drop in the calcium level -
for instance over 1 to 2 days.
If the calcium is subnormal for long periods of time (months or years), these muscle
symptoms may lessen but other problems may eventually develop - for instance lens
cataracts (affecting vision), dry skin and hair, brittle nails and chronic tiredness. In
children, enamel on the teeth may not develop properly and other more serious problems
affecting leaning ability and behavior may be seen.
For all these reasons, it is necessary to use specific treatment to restore the calcium level
towards normal in any person with a significantly low blood level of calcium.
Why does the calcium level fall?
Normally the calcium level is kept in the normal range by the action of a hormone
produced by the parathyroid glands. These are 4 small pieces of tissue (each the size of
a grain of rice) which are situated on either side of the thyroid gland in the neck. If there is
a deficiency of the hormone (called parathyroid hormone, or PTH for short), then the
blood level of PTH fails and insufficient calcium is absorbed from the food so that the
blood level of calcium eventually falls to levels below normal.
While there are several causes of hypocalcaemia, the commonest is due to damage to
the parathyroid glands (for instance after surgery for goiter) or failure of the glands to form
properly during fetal development. Antibodies may also develop against some tissue
component of the parathyroid gland, affecting the ability of the glands to make sufficient
Occasionally hypocalcaemia occurs because of tissue insensitivity to PTH. In such
cases, the parathyroid glands are working normally but there is an impaired response of
the tissues, and insufficient calcium is absorbed from the food, urine or bone - so that the
calcium level in the blood stream becomes subnormal.
What treatment is needed to keep the calcium normal?
Usually specific medication is needed, since simply taking a high content of dietary
calcium (as in milk, cheese etc), or extra calcium pills, will not be sufficient to restore the
The usual treatment is vitamin D - most often calcitriol (also known as
Rocaltrol) or calcidiol. These forms of vitamin D are very powerful chemicals which act on the intestine
to increase the amount of calcium (and phosphate) absorbed from the food. They also
act on the kidney and bone tissues, the net effect of which is to further increase the blood
level of calcium towards normal.
To be sure there is a sufficient supply of calcium in food, your doctor will often prescribe a
calcium pill, as well as vitamin D (for example, Oscal or calcium Sandoz). The actual dose
of vitamin D very much depends on the severity of the problem, with daily doses varying
from 0.5 to around 2.0 µg calcitriol daily, depending upon the blood level of calcium.
The aim of the treatment is to raise the blood calcium level into the normal range, usually
2.1 to 2.3 mmol/L. If the level is maintained in this range, all the above symptoms should
disappear and there would be little or no risk of complications. Usually the calcium level in
the blood needs to be measured several times after starting treatment.
Once stable and in the desired range, the blood level need be checked less often, say
once or twice a year in most cases. After making a dose change, it is also wise to
recheck the calcium level - for example 1-2 weeks later.
Are there risks from the treatment?
The main risk for vitamin D/calcium pill treatments is excessive correction of the calcium
producing an abnormally high blood calcium level (hypercalcaemia).
This should not happen provided the effects of treatment are carefully monitored but it is
very important that you understand how to recognize a high calcium level and what to do if
it happens. Small increases above normal (say 2.6-2.7) cause no ill effects but levels
above this may cause thirst, increased volumes of urine (including the need to rise at
night to pass urine), sometimes fatigue with loss of appetite, leading to nausea and
vomiting. Constipation can occur.
If you develop these symptoms, or you are suspicious of any one of them, you should
have a blood calcium level checked promptly.
Should the level be raised, it is important that you stop taking the vitamin D/calcium
A lower dose of pills can usually be recommenced a few days later, and arrangements for
rechecking calcium levels after you restart treatment need to be made.
Are there things I can do for myself or other things I should know?
Usually there are no dietary restrictions. However, if you decided to change your dietary
intake of dairy products (milk, cheese, yogurt etc) it could affect the blood calcium level,
and it would be wise to recheck it.
It is a good idea to record the calcium result and understand the small fluctuations that
can occur over the years. Remember that it is the "corrected calcium" level that should
be in the 2.1-2.3 range.
Eventually you will learn to make appropriate changes in treatment (in consultation with
your doctor) to keep the calcium levels in this range.
Some drugs will interfere with your vitamin D/calcium medication. For instance "fluid pills"
(especially thiazide diuretics), lithium and corticosteroids
may alter the tissue responses
to vitamin D.
If in doubt arrange to have a blood calcium check after you have been on any new
medication for 2-3 weeks.
In pregnancy, and during breast feeding, there may be additional demands for calcium.
However any change in dose of vitamin D/calcium will be dependent on the blood calcium level which needs to be checked more often (e.g. 3 monthly and soon after
commencing breast feeding).
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