Hi Peadar,
This is a question that has exercised us as well, prompted by the need
to monitor possible vitamin D excess. Nothing in the literature quite
fits the bill and in our (outpatient) population the receipt of
accurate 24 hour urine collections is even more of a fantasy than it
is for most labs. I've added in magnesium and zinc, for good measure.
I also looked at early morning first void random urines, but the
problem there is that they do tend to be more concentrated and
therefore less representative of the physiological situation.
We measure urine calcium, phosphorus, magnesium and zinc, in early
morning second void random urine samples.with the results expressed as
the molar ratio to creatinine. Reference ranges (n = 225) are:
UCa/Cr 0.25 – 0.60 mol Ca /mol creat
UPO4/Cr 1.46 – 4.75 mol PO4 /mol creat
UMg/Cr 0.50 – 0.85 mol Mg /mol creat
UZn/Cr 17 – 1624 umol Zn/mol creat (population mean for zinc was 644)
It's a little difficult to extrapolate to Trevor's New Zealand ranges!
Urine calcium can be used in the assessment of vitamin D status; if
the serum vitamin 25-hydroxy cholcalciferol is > 200 nmol/L and the
UCa/Cr is > 0.65, that is evidence for vitamin D toxicity.
Urine phosphate essentially reflects dietary intake of phosphorus, but
varies with age, muscle mass, renal function, PTH secretion and time
of day. In elevated PTH states serum Ca will be high, serum PO4 will
be low, with increased urine PO4, (reflecting the phosphaturic action
of PTH and vitamin D which increase the clearance of PO4 by the
kidney).
While a normal result does not exclude magnesium deficiency, a low Mg
value in urine suggests poor Mg intake. Phosphate depletion can be a
cause of concurrent magnesium loss.
The wide reference interval (17 - 1624 mol/mol creatinine) reflects
the poor intake of zinc in many subjects, combined with the effect of
zinc wasting into the urine.
I'd be interested to know if other list members have tried to
calculate these ranges.
Nick Miller
London
On 14/11/2012, Dr Peadar McGing <[log in to unmask]> wrote:
> Dear colleagues,
> I am looking for some help regarding adult reference intervals for urine
> calcium to creatinine ratio and phosphate to creatinine ratio.
> I would appreciate if you could send me the reference ranges you use if you
> report these parameters. I have some information from literature searches
> but not many actual ranges for adults, and more ambiguity than I would like
> in what I have found. The source of your range would also be useful.
> Thank you all in anticipation.
>
> best wishes.
>
> Peadar
>
>
> Dr Peadar McGing, FRCPath EurClinChem,
> Principal Biochemist,
> Biochemistry Dept., Mater Misericordiae University Hospital,
> Eccles Street, Dublin 7, Ireland.
> Tel: (+353 1)8032374; Fax: (+353 1)8034781.
>
>
>
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