Serum versus plasma hormone assay

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Evan - 09 Oct 2005 18:15 GMT

Would there be any appreciable benefit in assaying a hormone (in
general) in plasma as opposed to serum (or vice versa).

Also, urinalysis is often used. Aside from the much less technical or
invasive method of collecting urine over blood, does urine provide any
benefits for hormone analysis?

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Robert - 09 Oct 2005 20:00 GMT

> Would there be any appreciable benefit in assaying a hormone (in
> general) in plasma as opposed to serum (or vice versa).
>
> Also, urinalysis is often used. Aside from the much less technical or
> invasive method of collecting urine over blood, does urine provide any
> benefits for hormone analysis?

It varies based on the hormone. In general it is preferable to use serum
which is cleaner as most of the clottable proteins are removed.
Urine is water and hormones would thus be dependent on diluting effects.
There is a problem with specificity and sensitivity with urine. Serum
pregnancy testing is more sensitive than urine testing with the same
identical reagent kit.
Urine hormones like cortisol is termed "urinary free cortisol" meaning it is
free of carrier proteins. Alterations in carrier proteins in blood may alter
hormone concentrations. Urine does not allow the passage of carrier proteins
so all you have is the hormone.
It is thus easier to interpret urine cortisol levels better than blood
cortisol levels.

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