Dear Colleagues,
To follow on from Rita's message about the common reference interval for sodium I Australia an New Zealand:
When performing a reference interval study for serum sodium (direct or indirect methods) at a single site the range will approximately 8 or 9 mmol/L (eg 136 - 144 mmol/L a range of 9; or 136 - 143 a range of 8). This includes within and between subject biological variation and the analytical variation (over the time of the study) of the instrument(s) used to perform a study. For a shared reference interval, the between lab and between method analytical variation needs to be added which will make the range wider. The AACB range (135 - 145 mmol/L, range 11 mmol/L) allows a bias of approximately +/- 1 mmol/L for individual labs without increasing flagging rates unreasonably at that lab. Of course the wider range will reduce the flagging rate below 2.5% at either end of the range (for healthy subjects) for any individual lab and one or both needs of the range, depending on the magnitude and direction of any lab bias compared with the midpoint of the reference interval.
There are compromises with common reference intervals; but also clear benefits to labs and users.
The decision to implement the common intervals needs to be taken by individual labs aware of their analytical performance (especially bias) and any important population differences.
Regards,
Graham
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Rita (Andrea) Horvath
Sent: Thursday, 1 June 2017 8:04 AM
To: [log in to unmask]
Subject: Re: Sodium reference range
In Australia the harmonised RI for Na is 135-145 mmol/L - for more details and paediatric harmonised RIs see the full report on harmonisation of terminology and common RIs at our College's website: https://www.rcpa.edu.au/Library/Practising-Pathology/PTIS/APUTS-Downloads/Chemical-Pathology/SPIA-Chemical-Pathology-Reporting-Terminology-(1)
Kind regards, Rita Horvath
________________________________________
From: Clinical biochemistry discussion list [[log in to unmask]] on behalf of Michael Petchey [[log in to unmask]]
Sent: Wednesday, May 31, 2017 6:56 PM
To: [log in to unmask]
Subject: Re: Sodium reference range
It was a consensus range derived from what was in use at a wide selection of labs. Lab data suggests that the chosen lower limit may be below what was observed especially for GP patients.
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