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LABORATORY SERVICES
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MEMORANDUM
th
DATE:
19 July 2010
TO:
Clinicians/Healthcare Professionals
FROM:
Prof. Andrea Rita Horvath, Clinical Chemistry Department, SEALS North
SUBJECT:
Corrected Calcium released as a new orderable test in eMR
Dear Colleague,
Please note that as from 19th July 2010, Corrected Calcium can be requested in eMR for SEALS North and
Central.
When Corrected Calcium is requested, on the laboratory report Corrected Calcium, Total Calcium and
Albumin results will be provided. No Corrected Calcium calculation will be produced if calcium or albumin is
requested alone.
Background and rationale:
At physiological pH albumin binds approximately 45% of total serum/plasma calcium. Variation in albumin
concentration therefore alters the concentration of total calcium while the concentration of the physiologically
active ionized calcium remains constant. Various equations have been used to adjust total calcium for albumin to
reflect the “true” calcium status, and results obtained this way are called Corrected Calcium or adjusted calcium.
However, these equations are dependent on the calcium and albumin methods used in the laboratory(1).
Therefore SEALS has derived its own validated formula which provides a more reliable estimate of the biological
calcium status of the patient.
Please note that other commonly used formulas, also accessible from the internet, might be based on different
calcium and albumin measurement methods and thus may give false results. Therefore we strongly advise you
(1)
not to use any of these formulas with Calcium and Albumin test results provided by SEALS! .
Limitations of Corrected Calcium:
The calculation formula was not validated in patients under the age of 18 years and may be unreliable in:
• patients with renal failure,
• critical illness,
• patients whose serum albumin is less than 30g/L or greater than 50g/L.
Therefore Corrected Calcium values in these patient subgroups are indicative and can be used as a guide only!
The recommended test for patients in these cases is ionised calcium (collection requirements are the same as for
a blood gas).
If you need further information please contact SEALS Clinical Chemistry staff:
SEALS North:
Prof. Andrea Rita Horvath, Prince of Wales Hospital, Tel: 9382 9078
Email: [email protected]
SEALS Central:
Dr. Vivienne Ellis, St George Hospital, Tel: 9113-3306
Email: [email protected]
(1)
James MT et al. BMC Clinical Pathology, 2008; 8:12 (www.biomedcentral.com/1472-6890/8/12)
SEALS
North I l Randwick/Sydney
Central l Kogarah/Sutherland
South I l Wollongong/Nowra/Shellharbour