I would like to know the minimal amount of hCG (human chorionic
gonadotropin) detectable by a home pregnancy test kit IN GRAMS.  The
amount is usually measured in mIU (milli International Units).  An
International Unit represents an amount of biological activity a
substance has, and varies from substance to substance.  In your
answer, please provide a conversion for IU's into grams for hCG.

Hello -

While it is quite likely that the exact molecular weight/IU ratio
differs from sample to sample (due to such factors as differential
glycosylation, cleavage, degradation, complex formation,
co-precipitated salts, etc) there are several suppliers who are
willing to list their conversions.

One company in China advertises their product at >= 3000 IU/mg:
http://www.ahtech.com.cn/chembio.html

Scripps Laboratories offers three grades of hCG ranging from 2000 -
11,000 IU/mg (the 11,000 IU/mg they consider to be >99% pure based on
an SDS-PAGE gel which is a technique for measuring protein purity,
among other things...):
http://www.scrippslabs.com/graphics/pdfs/hCG.pdf

Another company sells "highly purified" hCG with a potency of 9,000
IU/mg:
http://www.affiland.com/protein/hcg.htm

Oem concepts advertises their hCG at 16,000 IU/mg:
http://www.oemconcepts.com/fertilit.html

Research Diagnostics advertises the following:
>96% purity  = 14,000 IU/mg
20-35% purity = 3000 - 5000 IU/mg
35-65% purity = 5000 - 9000 IU/mg
http://www.researchd.com/humanag/scp111.htm

Antigensite, offers a >98% pure hCG at 14,000 IU/mg
http://www.antigensite.com/hcg.htm

BiosPacific offers >98% pure at 14,000 IU/mg
http://biospacific.com/datasheets/J1310012.HTM

So, given the array of different potencies, I would suggest first
disqualifying any of lower purity than our lowest high purity sample
(11,000 IU/mg).  I would also remove the repeat 14,000 IU/mL as this
makes me suspect that they are buying from the same supplier.  This
leaves us with 11,000 , 14,000, and 16,000, which roughly averages to
around the middle value of 14,000 IU/mg.

There is a also test site which gives a conversion factor of 100pg/1.1
mIU hCG (11,000 IU/mg):
http://scooter.cyto.purdue.edu/pucl_cd/flow/vol3/7/luminex/hcg.htm

Applying these numbers to the values found for the sensitivities of
home pregnancy kits (14000 IU/mg used for low value, 11,000 IU/mg used
for high value):

Home pregnancy tests range in sensitivity, from 20mIU/mL (1.42 - 2.2
ng/mL):
http://www.babyhopes.com/pregnancytests.html

to between 25-250 mIU/mL (1.8 - 23 ng/mL):
http://www.babyhopes.com/pregnancytests.html

and between 10-25 mIU/mL (0.7 - 2.3 ng/mL):
http://www.pregnancytesting.freeserve.co.uk/


Specialized tests can apparently measure down to 0.5 mIU/mL (around 35
- 45 pg/mL ):
http://www.hcg.info/assays.htm


As for a direct, cut the calculations, kind of answer, one supplier of
pregnancy tests offers a lower limit of 10-20 pg/ml for their home
pregnancy kit:
http://www.biotraces.com/Bio56.html


I hope that this answered your question, please feel free to ask for
clarification as needed.

synarchy


Search strategy:

Google: hCG iu/mg
        human chorionic gonadotropin iu/mg
        hCG iu/mL
        hCG pg/mL
        hCG sensitivity

As you yourself have mentioned, IU is a measure of activity. It is
activity relative to the activity of a standard reference preparation.
As far as I am aware, there is no correlation between IU and weight.

Would the hGC found in a human body have the same potency as the hGC
from a laboratory? I have no idea, but that factor would certainly
affect the answer.

Well, the hCG in a laboratory is from humans, so, the molecule itself
should have the same potency.  The question of potency per weight is
an issue of how pure the protein can be made before assaying it.