|
Headlines:
|
 |
Pregnancy test
A pregnancy test is done to determine whether or not a woman is
pregnant.
All tests currently available to depend on testing for the presence of beta HCG or
human chorionic gonadotropin in the blood or urine.
Pregnancy tests measure the levels of hCG in the blood or urine to
indicate the presence or absence of a fertilized egg. In particular,
most pregnancy tests employ an antibody that is specific to the
β-subunit of hCG (βhCG). This is important so that tests do not make
false positives by confusing hCG with LH and FSH. (The latter two are
always present at varying levels in the body, while hCG levels are
negligible except during pregnancy.)
This hormone is only released by trophoblastic tissue, which usually
is produced by a growing fetus and its associated placenta or, rarely,
from a choriocarcinoma or some other germ cell tumours.
False negative readings (from home kits) can result from the
sensitivity of the test being lower than the current concentration of
the HCG in the woman's urine. This can occur quite commonly before the
6th week of pregnancy (defined as 6 weeks from the last menstrual
period) - beta HCG levels rise exponentially in the first two months
or so of pregnancy so the earlier the test is performed, the higher
the chance of a false negative result.
False positive results can result from rare beta-HCG producing tumors
like choriocarcinomas.
Reference levels
A single HCG level cannot indicate a normal pregnancy. In a normal
pregnancy there is a regular increase of the HCG, so you need to see
more than one value before you can better understand what's going on.
Additionally, a single value cannot always tell you how far along the
pregnancy is, because of the wide range of blood HCG levels in
pregnancy.
Sample reference list for HCG levels in singleton pregnancies, based
on days past ovulation (DPO):
* At 14 DPO, the average HCG level is 48 mIU/ml, with a typical range
of 17-119 mIU/ml.
* At 15 DPO, the average HCG level is 59 mIU/ml, with a typical range
of 17-147 mIU/ml.
* At 16 DPO, the average HCG level is 95 mIU/ml, with a typical range
of 33-223 mIU/ml.
* At 17 DPO, the average HCG level is 132 mIU/ml, with a typical range
of 17-429 mIU/ml.
* At 18 DPO, the average HCG level is 292 mIU/ml, with a typical range
of 70-758 mIU/ml.
* At 19 DPO, the average HCG level is 303 mIU/ml, with a typical range
of 111-514 mIU/ml.
* At 20 DPO, the average HCG level is 522 mIU/ml, with a typical range
of 135-1690 mIU/ml.
* At 21 DPO, the average HCG level is 1061 mIU/ml, with a typical
range of 324-4130 mIU/ml.
* At 22 DPO, the average HCG level is 1287 mIU/ml, with a typical
range of 185-3279 mIU/ml.
* At 23 DPO, the average HCG level is 2034 mIU/ml, with a typical
range of 506-4660 mIU/ml.
* At 24 DPO, the average HCG level is 2637 mIU/ml, with a typical
range of 540-10,000 mIU/ml.
Accordingly, the key to interpreting the true value of HCG
measurements is to look at their progression. In general, the HCG
level will double every two to three days in early pregnancy.
|
|
|
|
Are you a doctor or a nurse?
Do you want to join the Doctors Lounge online medical community?
Participate in editorial activities (publish, peer review, edit) and
give a helping hand to the largest online community of patients.
Click on the link below to see the requirements:
Doctors Lounge Membership
Application |
|
Doctors can also perform quantitative serum beta HCG levels.
This is commonly done in cases of suspected abortion, where a reading
that is lower than the expected range of readings based on the
patient's stated last menstrual period would be highly suggestive of a
miscarriage.
Other uses of a quantitative beta HCG reading are in evaluation of
ectopic pregnancy and in trophoblastic and other germ cell tumors.
|
send
to a friend
printer
friendly version
