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Discriminatory beta-hCG level

Posted by Dr KAMAL DEEP on August 16, 2010

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When the last menstrual period is unknown, serum b-hCG testing is used to define expected sonographic findings. Each institution must define a b-hCG discriminatory value, that is, the lower limit at which an examiner can reliably visualize pregnancy. At most institutions, a concentration between 1,500 and 2,000 IU/L represents this value.

 

Units in the above diagram is in IU/ML.So maximum levels are 120 IU/ml OR 120,000 mIU/ml OR 120,000 IU/L at 8 weeks of gestation in the above diagram.

Distinct profiles for the concentrations of human chorionic gonadotropin (hCG), human placental lactogen (hPL), and corticotropin-releasing hormone (CRH) in serum of women throughout normal pregnancy.Because hCG circulates as multiple highly related isoforms with variable cross-reactivity between commercial assays, there is considerable variation in calculated serum hCG levels among the more than 100 assays. Peak levels reach about 100,000 mIU/mL OR 100 IU/MLbetween the 60th and 80th days after the last menses (see Fig. 3–26). Beginning at about 10 to 12 weeks’ gestation, maternal plasma levels of hCG begin to decline, and a nadir is reached by about 20 weeks. Plasma levels are maintained at this lower level for the remainder of pregnancy.Current serum and urine pregnancy tests that use enzyme-linked immunosorbent assays (ELISAs) are sensitive to levels of chorionic gonadotropin of 10 to 20 mIU/mL

1. There has been much improvement in the early diagnosis of ectopic pregnancy using vaginal sonography. Its use results in earlier and more specific diagnoses of uterine pregnancy than abdominal sonography, and it has become the imaging method of choice in early pregnancy.

A.Using a vaginal transducer allows ultrasonic detection of a uterine gestation as early as 1 week after missed menses(5 WEEKS GESTATION).

B.When serum chorionic gonadotropin (B-hCG) levels exceed 1000 mIU/mL or 1 IU/ML, a gestational sac is seen half the time (De Cherney and Eichhorn, 1996). Criteria include identification of a 1- to 3-mm or larger gestational sac, eccentrically placed in the uterus, and surrounded by a decidual–chorionic reaction. A fetal pole within the sac is diagnostic, especially when accompanied by fetal heart action1.

The choice of diagnostic algorithm applies only to hemodynamically stable women; those with presumed rupture should undergo prompt surgical therapy. In a woman in whom ectopic pregnancy is suspected because of pain, bleeding, and a positive pregnancy test, performance of vaginal sonography is a logical first step. If a live uterine gestation is present, ectopic pregnancy is extremely unlikely. A heterotypic pregnancy is, of course, the rare exception (Hirsch and associates, 1992). Alternatively, if the uterus is empty, an ectopic pregnancy can be diagnosed based on visualization of an adnexal mass separate from the ovaries (Fig. 10–6).

In the event of a nondiagnostic study, subsequent management can be based on serial serum -hCG values and repeat vaginal sonography. A number of investigators have described discriminatory -hCG levels . Above these levels, failure to visualize a uterine pregnancy by transvaginal ultrasound indicates with high reliability that the pregnancy is either ectopic or nonviable. In a study by Barnhart and colleagues (1994), an empty uterus with a serum -hCG concentration of 1500 mIU/mL OR 1500 IU/L (1.5 IU/ML) or higher was 100-percent accurate in excluding a live uterine pregnancy. Thus, if the initial -hCG exceeds the discriminatory level, and no live intrauterine pregnancy is identified by vaginal sonography, the differential diagnosis is narrowed to a uterine pregnancy with a dead fetus versus an ectopic pregnancy. Early multifetal gestation, of course, remains a possibility. Uterine curettage will distinguish an ectopic from a nonliving uterine pregnancy. If an embryo, fetus, or placenta is identified, the diagnosis is apparent. When none of these is identified, tubal pregnancy is a probability.

If the initial B-hCG level is below the discriminatory value, early uterine pregnancy is a possibility, and serial assays of -hCG, in conjunction with repeat vaginal sonography, may prove useful. Kadar and Romero (1987) confirmed earlier work and demonstrated that in women with normal pregnancies, mean doubling time for -hCG in serum was approximately 48 hours(2 DAYS), and the lowest normal value for this increase was 66 percent (Table 10–2). In a series of 287 pregnant women, Barnhart and co-workers more recently (2004) reported a somewhat lower 48-hour minimum rise for a live intrauterine pregnancy of 53 percent, and a 24-hr minimum rise of 24 percent. Kadar and Romero concluded that failure to maintain this minimum rate of increased -hCG production, along with an empty uterus, was suggestive of an ectopic pregnancy. Thus, appropriately selected women in whom ectopic pregnancy is suspected, but whose initial -hCG is below the discriminatory level, may be followed expectantly. They are seen at 2- to 3-day intervals for further evaluation. If the -hCG level rises inappropriately, plateaus, or exceeds the discriminatory level without evidence of a uterine pregnancy by vaginal sonography, a live uterine pregnancy can be excluded. Then, distinction between nonliving uterine versus an ectopic pregnancy is made by uterine curettage, or in some cases, by endometrial biopsy. Barnhart and associates (2003) reported that biopsy was less sensitive than curettage.

3 Responses to “Discriminatory beta-hCG level”

  1. Veronica said

    Nicely Explained about HCG. Thanks for sharing this information

    Veronica Pitman
    HCG

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  3. ___123___Discriminatory beta-hCG level « Review of Critical Care Medicine___123___

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