Robert Lord wrote:
> I would be grateful for any advice regarding the use of urine samples in
> the diagnosis of this condition. We check up on the serum calcium of family
> members in addition to checking the urine calcium of the patient.
> Should a 24hr urine collection be used for this in the patient or is a
> random urine OK for use in the calculations (should the patient fast /
> second void?) (cut)
I believe 24 hour urine collections to be very unreliable. Ian Gunn and James
Wallace (Ann Clin Biochem 1992;29:52-58) and Stuckey et al (Clin Endocrinol
1987;27:525-533) both found that a plot of PTH against CaE separated patients
with familial benign ('hypocalciuric') hypercalcaemia from those with
hyperparathyroidism. After discarding the overnight urine the fasting patient
needs to collect a sample of the next voiding for calcium and creatinine and to
have blood taken for PTH and creatinine. A timed urine collection is not needed
to calculate CaE.
You are absolutely right to be checking the serum calcium of family members
when an asymptomatic patient with hypercalcaemia is under threat of the knife,
but it is probably worthwhile only if his or her results are close to or in the
FBH (FHH) area of the PTH vs CaE plot. Family studies can cause a lot of
anxiety, and can be difficult if children are involved.
We reported an interesting family with asymptomatic members having both
familial benign hypercalcaemia and benign hypocalcaemia (Ann Intern Med
1986;105:217-219). All had normal PTH and CaE values. Both conditions are now
known to be caused by abnormalities of the calcium-sensing receptor gene ( DA
Heath, Clin Endocrinol 1998;48:257-258). The author of this review pointed out
that unless both the benign hyper- and hypo-calcaemic variants are kept to the
front of one's mind, the wrong treatment may be given and patients may suffer.
Brian Payne
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