Page 16 - Medicine and Surgery

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12 Chapter 1: Principles and practice of medicine and surgery

Investigations Loop diuretics such as furosemide can be used in con-
These are aimed at assessing the severity of hypercal- junction with fluids to increase renal excretion of cal-
caemia to guide management and to look for the under- cium and prevent fluid overload.
lying cause. The serum calcium should be checked and Bisphosphonates can be used, which inhibit bone
corrected for serum albumin because only the ionised turnoverandthereforereduceserumcalcium.Steroids
calcium (not bound to protein) is active. The total serum may be used if the underlying diagnosis is a known
calcium is corrected as follows: malignancy, but is less useful if there is ectopic PTH
production.
If there is renal failure, early consultation with a
Corrected calcium = Measured calcium +
nephrologist is needed, as increased renal excretion
0.02(40 − serum albumin)
of calcium is often impossible or difficult to achieve
and dialysis may be required.
Mild hypercalcaemia (2.6–2.8 mmol/L) is suggestive Further management depends on the underlying

of primary hyperparathyroidism.
cause.
Moderatetoseverehypercalcaemiaismorecommonly

due to malignancy.
Blood should be sent for U&Es (to look for renal impair- Hypocalcaemia
ment), serum protein electrophoresis and Bence Jones
protein (to look for myeloma) and a PTH (parathyroid Definition
hormone) level. If the PTH level is normal or high, this Aserum calcium level of <2.2 mmol/L.
is diagnostic of hyperparathyroidism because it should
be suppressed in hypercalcaemia. A chest X-ray may
Aetiology
demonstrate malignancy or sarcoidosis. Serum phos-
phate may be helpful, as it tends to be low in ma- Hypocalcaemia may be caused by
vitamin D deficiency,
lignancy or primary hyperparathyroidism but high in
hypoparathyroidism (after parathyroidectomy, thy-
other causes. If PTH is low, PTH-like peptide can be
measured. roid or other neck surgery),
pseudohypoparathyroidism,
Other tests which may be useful include the following:
magnesium depletion by inducing end-organ PTH re-
Urinary calcium, which is raised in most causes

of hypercalcaemia, but relatively low (<100 mg or sistance or deficiency (causes include diuretics, alco-
2.5 mmol/day) in milk–alkali syndrome, thiazide di- holism and malnutrition),
hyperphosphataemia,
uretic use and FHH.
acute pancreatitis and severe sepsis,
Vitamin D and its active metabolites.

acute respiratory alkalosis,
Serum angiotensin converting enzyme (ACE), which

drugs, e.g. chemotherapy especially cisplatin, bispho-
may be raised in pulmonary sarcoidosis.
sphonates and
calcium chelators, e.g. citrate following large transfu-

Management
sions of blood.
This depends on the severity, whether acute or chronic
and the underlying cause. Any causative drugs should be
withdrawn. Pathophysiology
Patients should be assessed for fluid status and any Hypocalcaemia causes increased membrane potentials,

dehydration corrected. Rehydration reduces calcium which means that cells are more easily depolarised
levels by a dilutional effect and by increasing renal and therefore causes prolongation of the Q–T interval,
clearance. Intravenous saline is often needed because which predisposes to cardiac arrhythmias. It may also
many patients feel too nauseous to tolerate sufficient cause refractory hypotension and neuromuscular prob-
oral fluids and polyuria is common due to nephro- lems include tetany, seizures and emotional lability or
genic diabetes insipidus. depression.