Nicola,
It's a matter of getting a relaible estimate of the urine calcium
excretion. We use the second void early morning urine sample for
urine calcium, and also for urine magnesium, phosphorus and zinc.
The logic this thus:
1) It's impossible to obtain reliable 24 hour urine collections on
outpatients and, probably, on in-patients unless they are in a
metabolic ward (does anybody still have a metabolic ward?)
2) If you are looking for an exogenous substance or an abnormal
metabolite, then you need a concentrated urine specimen to exclude its
presence - hence the em urine collection
3) However, for urine calcium etc the first void em urine is not
representative of the daily excretion rate, so we take the second void
em urine and express the results as the molar ratio to creatinine.
Nick Miller
London
On 03/07/2013, Nicola Pullan <[log in to unmask]> wrote:
> Dear Mailbase,
>
> Can anyone explain the origin of the "fasting, second-void" urine sample for
> the assessment of familial benign hypercalcaemic hypocalciuria vs primary
> hyperparathyroidism?
>
> Particularly, why is it recommended that the sample is second-void rather
> than just fasting?
>
> Do any labs/endocrinologists recommend anything other than this when trying
> to distinguish between primary hyperparathyroidism and FHH?
>
> Best wishes,
>
> Nicola
>
>
> Nicola Pullan
> Clinical Scientist - Biochemistry
> Pathology Sciences Laboratory
> Southmead Hospital
> Westbury on Trym
> Bristol, BS10 5NB
>
> Email: [log in to unmask]
>
> Tel: 0117 32 38514
>
>
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