Dear Ahmed

 

You may have misunderstood the Harmony recommendation for calcium adjustment. The following is a response to a FAQ on the Pathology Harmony website:

 

                    4. Adjusted calcium 

Please could you advise on how to normalise the adjusted Calcium calculations to a mean calcium of 2.4 mmol/L? Please clarify what is meant by the term ‘normalised to a mean calcium of 2.4 mmol/L’. 

 

The method described in the Annals of Clinical Biochemistry (1996;33:55-58) was used by Pathology Harmony for the adjustment of serum calcium. The only difference is that following the generation of the least squares regression of calcium on albumin for the data collected the intercept on the y-axis is subtracted from 2.4 

This value is substituted into the calcium adjustment equation in the general form: 

Ca]adj = [Ca]tot – (x * [Alb]) + y 

where x is the slope of the regression line and y the intercept subtracted from 2.4 

The desired effect of this is to “normalise” the adjusted calcium values from various different platforms so that the mean of the normal population is 2.4, and since the distribution of adjusted calcium is reasonably Gaussian we have proposed a range of 2.2 – 2.6 mmol/L. 

 

In other words Harmony is using a published method which describes how to derive an appropriate equation from your methods and population as advocated by various contributors as the best approach to this problem. The normalization described does not invalidate this approach; it simply shifts the adjustment for each lab to a mean of 2.4 mmol/L which allows the adjusted calcium results to be comparable between labs and a harmonized reference range to be proposed.

 

I hope you will agree that this is a scientifically based approach but also a positive step towards improved lab to lab result transferability.

 

Best regards

Gethin 

 

Gethin Roberts

Cons Clinical Biochemist

01970 63(5784) WHTN 0-1822 5784
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