Calcium

Background

Calcium is the most prevalent cation in the body, it exists in three physiochemical states:-

1. Free (ionized) approx 50%
2. Protein bound (predominately to albumin) approx 40%

and

1. Complexed with small anions approx 10%.

Calcium concentration is tightly controlled by Parathyroid Hormone (PTH) and 1, 25-dihydroxyvitamin D.

Estimations of the serum levels of calcium are used in the diagnosis and treatment of parathyroid disorders, renal disease, a variety of bone disorders, carcinomas, acromegaly and pancreatitis.

Hypocalcemia commonly presents with neuromuscular excitability, eg tetany, paresthesia and seizures. Causes include hypoalbuminemia (pseudohypocalcemia – see below), chronic renal failure, hypoparathyroidism, magnesium deficiency and acute pancreatitis.

Hypercalcemia can present with fatigue, malaise and weakness when mild. Depression, apathy, inability to concentrate, nausea and vomiting may occur at higher levels. Causes include malignancy, hyperparathyroidism and Vitamin D overdose.

Reference ranges

Serum/Plasma: 2.1 – 2.6 mmol/L
Urine: 2.5 – 7.5 mmol/24hrs

Patient preparation

Serum/Plasma: avoid haemostasis

Specimen requirements

Sample type:

• Serum, lithium heparin plasma
• Plain 24 hour or random urine

Sample identification:

• Three patient identifiers from
  • Name
  • D.O.B.
  • Address
  • N.H.S. number
  • Unit Number
  should match on the specimen and request form. This check may be performed prior to centrifugation by the Central Sort department.

Turnaround time

2 hours