Thursday, April 9, 2009

How sensitive are "early" pregnancy tests?

How sensitive are so called early pregnancy tests?

Apparently not that sensitive. Quoting from medscape.com:
Quoted from Medscape.com:

"Regular hCG is neither the principal nor the sole hCGrelated molecule present in urine on the first day of the missed period, as demonstrated in multiple studies.[5-8] Studies show that a mixture of hCGrelated molecules is present, principally hyperglycosylated hCG, with lesser amounts of regular hCG, and much smaller amounts of free beta-subunit and beta-subunit core fragment. In this study we mimic this mixture as closely as possible. Manufacturers of OTCPTs design their products strictly to measure regular hCG and sometimes also free beta-subunit. They also determine the sensitivity of their products using regular hCG. Not surprisingly then, most OTCPTs have much lower sensitivity for hyperglycosylated hCG and beta-core fragment.[2,8] Five of the products evaluated here (Clearblue Easy Earliest Results, CVS One Step, E.P.T., Eckerd One Step, and First Response Early Result) were previously evaluated using pure hCG.[3] Their analytical sensitivities were 12.5, 50, 25, 50, and 6.3 mIU/mL, respectively, quite different from the analytical sensitivities in the current study, which used urine samples much more closely mimicking those of the first day of a missed period[2,8]: 25, 100, 100, 100, and 6.3 mIU/mL, respectively. At four of the five tested concentrations the sensitivity was greatly reduced. Manufacturers need to make OTCPTs based on the real mixture of hCGrelated molecules present in urine at the time of pregnancy detection and to make clinically accurate and relevant sensitivity claims based upon detection of this mixture rather than just regular hCG, which is predominantly present alone in the later trimesters of pregnancy.[2,3,5-8]"

The test which they are talking about that detects a mere 6.3mIU/mL is First Response Early Results. Personally they aren't my favorite because I feel like they need to dry before a faint line can be seen. In my experience anyway, that was the case.

From other studies I've read; the two OTC home pregnancy tests that are most sensitive to h-hCG (the earliest pregnancy hormone see
here) are first Fact Plus and second EPT. FRER is now claiming "detects the early form of the pregnancy hormone" I'm guessing this is h-hCG, so maybe it's up with those two now?

Quoted from "S. Davies et al / Clin Lab Med 23 (2003) 257–264":

It is not uncommon for a woman to have a negative urinary home pregnancy test result around the time of her missed menstrual period but a positive serum hCG result when
assessed a few weeks later. This discrepancy may be due to the insensitivity of
a home or point-of-care pregnancy test [3]. A similar situation may occur
when a woman has a positive early pregnancy test, but a repeat urine or
serum test approximately 1 week later is negative. This is due to early
pregnancy loss [8,9]. There also is a clear variance in the sensitivity of home
and point-of-care pregnancy test devices for detecting intact hCG and HhCG:
some tests poorly detect H-hCG (the key molecule in early pregnancy),
and others more efficiently detect H-hCG than intact hCG [3]. The data from
Butler et al [3] indicate that urine devices need to be formulated to optimally
recognize H-hCG.



More to come...

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