We had a very similar case about a year ago. The only difference was
that the lady had her last pregnancy test one week prior to the
ligation. No HCG test was done on the day of operation.
A review of the literature at that time gave me the impression that
either serum or urine tests will give you the same answer at about the
same time. Although the serum tests are more sensitive analytically, the
"normal" range of serum HCG in non pregnant women significantly overlaps
the ranges seen early in pregnancy. Therefore, you need to wait at least
five to seven days after conception to have a serum HCG result that can
be interpreted as positive for pregnancy. This is about the same time as
required for the urine pregnancy test to become positive.
Of course, one should emphasize the need for first morning urine
collection because of the potential dilution of HCG in random urines
during the day!
Although I presented these findings to the obstetricians, they decided
to order quantitative serum HCG's. Therefore, the lab now does serum HCG
test whenever it is ordered by OB per our "good neighbor policy".
Geza
Stephen Davis wrote:
>
> We recently encountered a case where a lady admitted for sterilisation had a negative urine pregnancy test and underwent sterilisation. She was subsequently shown to be pregnant with dates consistent with conception occurring prior to the procedure.
>
> Should a sensitive serum test have been used rather than a urine test? Does anyone know of cases where laboratories/hospitals have been criticised for using urine test rather than serum in such circumstances?
>
> Steve Davis
> Principal Biochemist
> Department of Clinical Biochemistry
> East Glamorgan General Hospital
> Church Village
> PONTYPRIDD
> Mid Glamorgan
> CF38 1AB
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