Are laboratories reporting serum quantitative hCG results correctly?

BACKGROUND: Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone that exists in multiple forms. Immunoassays commonly used in clinical laboratories measure intact hCG, total beta hCG (intact hCG + hCG free beta-subunit), and/or hCG free beta-subunit. Measurement of serum concentrations of hCG is useful for confirmation and monitoring of pregnancy, diagnosis of trophoblastic diseases and monitoring of the efficacy of treatment, and prenatal screening. Correctly reporting results for the various forms of hCG is clinically important. METHOD: We prepared samples by addition of intact hCG and hCG free beta-subunit to an essentially hCG-free human serum matrix. The samples were analyzed by participant laboratories using various immunoassay methods. RESULTS: We identified errors in participant reporting of intact hCG results as total beta hCG (9.3%; 22 of 235 laboratories) and total beta hCG as intact hCG (13.1%; 8 of 61 laboratories). CONCLUSIONS: Many factors contribute to the erroneous reporting of hCG results, including (a) the complexity of hCG molecule and confusion of nomenclature on the various forms of hCG; (b) laboratory personnel's lack of awareness of the distinctions of the forms of hCG and failure to recognize the specificity of assays for their measurement; (c) lack of clarity and uniformity in manufacturers' reagent labeling; and (d) most product inserts' lack of information on the specificity of each method to the various forms of hCG.     

Free alpha-subunit, free beta-subunit of human chorionic gonadotropin (hCG), and intact hCG in sera of healthy individuals and testicular cancer patients.

To determine the serum concentrations of human chorionic gonadotropin (hCG), its free beta-subunit (hCG beta), and the free alpha-subunit (free alpha) common to all human glycoprotein hormones under physiological and pathological conditions, we developed monoclonal antibody-based immunoenzymometric assays. Free alpha-subunit was detected in the sera of all healthy individuals of both sexes; hCG was measurable in sera of 54% of the men, and 46% were positive for free hCG beta; in nonpregnant women, 69.5% were positive for hCG, 68.4% for the free beta-subunit. Pathological conditions, i.e., hCG-producing tumors, were studied in vitro and in vivo. In vitro, the concentrations of hCG, free hCG beta, and free alpha in tissue-culture supernates of a choriocarcinoma cell-line ("JAR") showed a parallel pattern during time-course analysis. In vivo, in long-term follow-up studies of 13 patients with testicular cancer, serum concentrations of the three analytes paralleled each other, whether the disease was in remission or not. Because of a selective increase of free hCG beta and free alpha in 27% of seminomatous tumor patients and in 13% of the nonseminomatous patients, the percentage of tumor-marker-positive sera was increased from 15% to 42% and 57% to 70%, respectively, by the additional measurement of free hCG beta and free alpha. Thus hCG, free hCG beta, and free alpha are physiologically present in a high percentage of the sera from healthy men, and the determination of free hCG beta and free alpha, although not of prognostic value, improves the diagnostic possibilities in patients with testicular cancer.     

Choriogonadotropin and its beta subunit separated by hydrophobic-interaction chromatography and quantified in serum during pregnancy by time-resolved immunofluorometric assays

Concentrations of human choriogonadotropin (hCG) and its free beta subunit (beta hCG) were measured in serum by highly sensitive and specific time-resolved immunofluorometric assays (IFMAS). The results were confirmed by completely separating beta hCG and hCG by a novel method based on hydrophobic-interaction chromatography. We used three monoclonal antibodies in two different combinations. In both assays an antibody reacting with both free beta hCG and with intact hCG was immobilized onto the wall of a microtiter strip well. For assay of intact hCG we used as the indicator antibody an antibody against the alpha subunit, labeled with a europium chelate. For assay of beta hCG we used an indicator antibody that reacted only with the free beta subunit. hCG cross-reacted in the assay of beta hCG by 0.6%. Quantifying hCG in serum after in vitro fertilization showed that, seven to eight days after embryo transfer, the hCG concentration started to increase, thereafter increasing with a doubling time of 1.9 days during the following three weeks. hCG concentrations in serum peaked six to 10 weeks later, corresponding to eight to 12 weeks after the last menstrual period. Throughout pregnancy, measurable amounts of beta hCG were present in serum. The highest beta hCG/hCG ratio (maximum 7.3%, median 3.0%) was observed during early gestation. During the fourth to 13th weeks after the last menstrual period the ratio of beta hCG/hCG decreased gradually, being 1.0% during the second and third trimesters.     

Polypeptide nicks cause erroneous results in assays of human chorionic gonadotropin free beta-subunit.

Pregnancy and trophoblastic disease testing laboratories measure human chorionic gonadotropin (hCG; human choriogonadotropin) free beta-subunit to screen for Down syndrome and to diagnose persistent trophoblastic disease (invasive mole and choriocarcinoma). The results from various laboratories, however, vary widely for similar groups of patients. Average concentrations of free beta-subunit reported for persistent trophoblastic disease, for instance, range from 2.6% to 37% of total hCG. On hCG and its free beta-subunit, peptide bonds can be missing between beta-subunit residues 44 and 45 or between residues 47 and 48 (nicked molecules). To explore the possibility that the disparity in the reported concentrations of free beta-subunit was due to differences in recognition of nicked molecules by different antibodies, we generated 0% and 100% nicked beta-subunit standards and investigated their recognition in three separate immunoassays of free beta-subunit. The immunoassay with antibody 1E5 did not recognize nicked beta-subunit (4% cross-reactivity with nicked beta-subunit) and thus detected only intact beta-subunit. The immunoassay with antibody FBT11 gave similar results with nicked and nonnicked thus standards (96% cross-reactivity with nicked beta-subunit), as did the assay with antibody B204 (73% cross-reactivity with nicked beta-subunit). These two immunoassays thus measured total (nicked + nonnicked) beta-subunit. We used the three immunoassays to examine sera from normal pregnancy, Down syndrome pregnancy, hydatidiform mole, and persistent trophoblastic disease, all of which contain nicked and nonnicked beta-subunit molecules. The results obtained resembled the studies with nicked beta-subunit standards. The results from the FBT11 and B204 assays (total beta-subunit) were highest, results from the 1E5 assay (intact molecules only) being as much as 10 times lower. We conclude that nicks in beta-subunit and the extent of recognition of nicked molecules by different antibodies affect the concentrations reported for free beta-subunit.     

Discordant results in human chorionic gonadotropin assays.

Discordance has been reported in human chorionic gonadotropin (hCG) concentrations measured by different immunoassay kits. We examined the results for 40 serum samples assayed with 10 different hCG immunoassay kits. Results varied considerably. Individual sample results varied by as much as 58-fold. Average results for different kits varied by as much as 1.4-fold for pregnancy (20 samples) and 2.2-fold for trophoblast disease (20 samples) serum. We investigated the causes of this discordance. hCG or hCG beta are general names for mixtures of hCG, hCG alpha, or hCG beta immunoreactive molecules in serum. These mixtures include regular hCG, nicked hCG (missing peptide linkages at beta 44-45 or beta 47-48), carbohydrate variants of hCG, hCG missing the beta-subunit C-terminal segment, free beta-subunit, beta-core fragment, and free alpha-subunit. We prepared standards for each of these major variants and measured their reactivities in the 10 hCG immunoassay kits. Free beta-subunit reactivity varied from nonrecognition (anti-beta:anti-alpha type kits; Hybritech Tandem-R and others) to overrecognition (one kit had five-fold greater affinity for free beta than for hCG). Kits with antibodies to beta-subunit C-terminal segment (Organon NML and others) failed to recognize hCG missing this segment, a component of serum hCG in trophoblast disease. Kits with anti-hCG antibodies (Serono MAIA-clone and others) had minimal recognition of nicked hCG (12%), a component of all serum hCG samples, and consistently gave the lowest values with all serum samples. We conclude that differences in recognition of nicked hCG, free beta, and these other hCG variants cause discordance in hCG immunoassay results.     

An algorithm for testing and reporting serum choriogonadotropin at clinically significant decision levels with use of "pregnancy test" reagents

We present an algorithm for monitoring the concentration of human choriogonadotropin (hCG) in serum at various clinical decision levels with use of fast, simple, and cost-effective qualitative pregnancy test reagents for hCG in serum. Based on correlation between laboratory data and clinical observations described in the literature, the following concentrations of hCG in serum can be considered as clinically significant decision levels: 5 int. units/L to exclude or "rule out" the presence of increased hCG; 25 int. units/L for "confirming pregnancy" or confirming the presence of increased hCG from sources other than the trophoblast; and 6500 and 82 500 int. units/L to enhance the sonographic diagnoses of ectopic pregnancies and molar pregnancies, respectively. We used Tandem Icon II (Hybritech) pregnancy test reagents and evaluated the reagents for possible "false-positive" findings at the 25 int. units/L limit of hCG detectability by analyzing 100 post-menopausal and more than 4000 premenopausal serum specimens. The performance of the reagents was validated also at 5 int. units/L and at limits of hCG detectability greater than 25 int. units/L.     

Beta-hCG vs intact hCG assays in the detection of trophoblastic disease

We describe a case of choriocarcinoma in which increased concentrations of beta-choriogonadotropin subunits in serum indicated recurrence of metastasis long before the tumor could be confirmed by visualization techniques, while intact choriogonadotropin remained normal (less than 5 int. units/L). Therefore, detection or monitoring of choriocarcinoma requires the assay of free beta-hCG subunit or an assay that measures both the free beta-subunit and intact choriogonadotropin.     

Immunoassays for quantifying choriogonadotropin compared for assay performance and clinical application.

We examined calibration and accuracy, precision, sensitivity, specificity, and "hook" effects for recently revised automated choriogonadotropin (hCG) immunoassay systems (Baxter-Dade Stratus II, Abbott IMx intact hCG and total beta hCG) and compared them with a widely used immunoradiometric assay (Hybritech). We estimated hCG in pregnant women, women with trophoblastic disease, nonpregnant young and menopausal women, normal men, and men with testicular tumors. We found clinically unimportant differences in calibration (all calibrated to the 3rd International Standard). Detection of hCG by all four assays was limited by their responses in serum from nonpregnant women and men. Precision within-run was best for the automated instruments, but all four assays had similar between-run precision. The Hybritech, Stratus, and IMx intact assays are specific for intact hCG. The IMx total beta assay quantifies both free beta subunit and beta subunit present in intact hCG. There is a clinically important hook effect in the Hybritech assay but not the Stratus or IMx assays (to 1.2 x 10(6) int. units/L). Results for pregnant women were similar by all four assays. We measured "hCG" to 8 int. units/L in menopausal women, which weakly correlated with concentrations of lutropin and follitropin and was, in part, explained by crossreactivity. There was no sample-probe carryover in either instrument. We found the IMx diluting module as well as results at the extremes of the IMx calibration curves (less than 10, 800-1200 int. units/L) unreliable but encountered no such problems with the Stratus system. Both automated systems involve batch analyzers with limited throughput but provide hCG concentration estimates much more quickly than the Hybritech assay can.     

Thyroid function during pregnancy

BACKGROUND: This Case Conference reviews the normal changes in thyroid activity that occur during pregnancy and the proper use of laboratory tests for the diagnosis of thyroid dysfunction in the pregnant patient. CASE: A woman in the 18th week of pregnancy presented with tachycardia, increased blood pressure, severe vomiting, increased total and free thyroid hormone concentrations, a thyroid-stimulating hormone (TSH) concentration within the reference interval, and an increased human chorionic gonadotropin (hCG) beta-subunit concentration. ISSUES: During pregnancy, normal thyroid activity undergoes significant changes, including a two- to threefold increase in thyroxine-binding globulin concentrations, a 30-100% increase in total triiodothyronine and thyroxine concentrations, increased serum thyroglobulin, and increased renal iodide clearance. Furthermore, hCG has mild thyroid stimulating activity. Pregnancy produces an overall increase in thyroid activity, which allows the healthy individual to remain in a net euthyroid state. However, both hyper- and hypothyroidism can occur in pregnant patients. In addition, two pregnancy-specific conditions, hyperemesis gravidarum and gestational trophoblastic disease, can lead to clinical hyperthyroidism. The normal changes in thyroid activity and the association of pregnancy with conditions that can cause hyperthyroidism necessitates careful interpretation of thyroid function tests during pregnancy. CONCLUSION: Assessment of thyroid function during pregnancy should be done with a careful clinical evaluation of the patient's symptoms as well as measurement of TSH and free, not total, thyroid hormones. Measurement of thyroid autoantibodies may also be useful in selected cases to detect maternal Graves disease or Hashimoto thyroiditis and to assess risk of fetal or neonatal consequences of maternal thyroid dysfunction.     

Use of serum FSH to identify perimenopausal women with pituitary hCG

BACKGROUND: Human chorionic gonadotropin (hCG) tests are performed on many female patients before performing medical procedures or administering medications that may harm a fetus. hCG of pituitary origin has been shown to increase with age. Therefore, mild increases in serum hCG in an older patient can be of pituitary origin and does not necessarily indicate pregnancy. The inability to rule out pregnancy in perimenopausal women can create clinical confusion and may delay needed therapies. Our objective was to determine the diagnostic utility of serum follicle-stimulating hormone (FSH) concentrations to rule out hCG of placental origin in perimenopausal women with a low concentration of serum hCG (5.0-14.0 IU/L). METHODS: Seven testing centers performed 39 742 physician-ordered serum quantitative hCG tests over a 15-month period. From these, 100 samples from women 41-55 years of age with serum hCG concentrations 5-14 IU/L were identified. We performed FSH testing and patient chart review for each sample. RESULTS: Twenty-three patients were found to have hCG of placental origin (pregnancy, resolving abortion, or gestational trophoblastic disease), and in those cases serum FSH was 0.4-43.8 IU/L. An FSH cutoff of 45.0 IU/L identified hCG of placental origin with 100% sensitivity and 75% specificity. FSH >45 IU/L was never observed when hCG was of placental origin (negative predictive value). CONCLUSIONS: These data indicate that quantitative serum FSH can be used to rule out pregnancy and hCG of placental origin in women 41-55 years of age with mild increase in serum hCG concentrations.     

Charge variants in serum and urine hCG

BACKGROUND: All serum and urine pregnancy tests sold in the United States are calibrated against the WHO 3rd and 4th International Standards (3rd and 4th I.S.) of Human Chorionic Gonadotropin (hCG). These standards have been isolated from pregnancy urine; however, they are used to calibrate, and generate antibodies used in both urine and serum hCG tests. hCG molecules may vary in sialic acid content; this changes the acidity of the molecule. Published studies have shown that these carbohydrate elements may alter recognition of hCG in different serum and urine hCG tests. We investigated the charge variants of hCG in serum and urine samples, and in hCG standards. METHODS: Samples were analyzed by preparative isoelectric focusing. Charge variants of hCG were quantitated using the DPC Immulite hCG assay. RESULTS: A difference was observed in the proportion of charge variants in urine and serum samples. There was a significantly higher proportion of more-acidic variants in the urine samples. CONCLUSIONS: Urine-derived standards may not be representative of serum hCG and therefore may not be appropriate for calibrating serum assays. Variation among hCG test results when using different immunoassays has been a persistent problem for years. Additional studies are needed to focus on the molecular dissimilarity of urine and serum hCG, as well as other factors, to determine their significance and contribution to the problem of interassay variation when comparing hCG results.     

Qualitative beta-hCG urine assays may be misleading in the presence of molar pregnancy: a case report

Molar pregnancy is a rare complication of pregnancy and the diagnosis is usually confirmed with a markedly elevated beta-hCG and a "snowstorm" appearance on pelvic ultrasound. Patients frequently present with a positive pregnancy test, vaginal bleeding, nausea and vomiting. A 23-year-old woman presented to our Emergency Department with a history of 7 weeks of intermittent vaginal bleeding and 1 h of peri-umbilical abdominal pain. She reported that 7 weeks before this visit she was diagnosed with a miscarriage. The bedside qualitative urine human chorionic gonadotropin (hCG) test that we performed was negative, but the quantitative serum hCG was markedly elevated. Ultrasound and operative findings confirmed the diagnosis of molar pregnancy. We conclude that rapid urine qualitative hCG assays may not be reliable in the presence of markedly elevated hCG levels found in molar pregnancy.     

The need for a quantitative urine hCG assay

BackgroundThe USA uniquely does not use quantitative urine human chorionic gonadotropin (hCG) tests despite being invaluable in pregnancy testing and in monitoring cancer patients. We look at current hCG tests and their detection of the degraded forms of hCG predominant in urine. We examine levels of urinary hCG, its usefulness in pregnancy testing, and advantages of urine testing in false positive hCG cases and cancer cases.MethodshCG assays were blindly evaluated at 10 laboratories running different methodologies. Daily urine samples from 164 women were collected through 5 menstrual cycles or until pregnancy was achieved. Urines were assayed for total hCG. We also examined the use of quantitative urine hCG in confirming false positive serum hCG results in 80 clinical cases.ResultsOnly the Siemens Immulite test was shown to detect the degraded forms of hCG present in urine. This test equally recognized urine and serum hCG. We investigated background hCG in 9026 urines, the mean hCG level was 0.04 IU/L, and the 99th centile was 1.4 IU/L. In cycles where pregnancy was achieved, hCG could be detected in urine at 24.6 days of a 28.7 day menstrual cycle. At this time, the average hCG was 6.02 IU/L, setting a sensitivity level for quantitative urine hCG tests to detect pregnancy. Quantitative urinary hCG proved critical in detecting cancer in 3 of 80 cases complicated by false positive serum hCG.ConclusionsThe need for a quantitative urine hCG assay is undeniable and we invite manufacturers to produce a quantitative urine hCG test.     

Evaluation of an assay of the free beta-subunit of choriogonadotropin and its potential value in screening for Down's syndrome.

In this study I investigated the analytical and clinical performance of the measurement of the free beta-subunit of choriogonadotropin (hCG) in normal pregnancies and in pregnancies affected by Down's syndrome. Free beta-hCG in maternal serum has been shown to be increased in Down's syndrome-affected pregnancies and is proportionally increased in more cases than is total hCG. This study confirms previous findings of low concentrations of unconjugated estriol and alpha-fetoprotein in maternal serum in Down's syndrome-affected pregnancies. Using a multivariate risk analysis of maternal age and concentrations of alpha-fetoprotein, unconjugated estriol, and hCG in maternal serum, I determined that, at a risk cutoff value of 1 in 300, 52% of Down's cases could be detected with total hCG in the calculation, compared with 66% with the free beta-hCG concentration. The false-positive rate was 5.9% in both cases. Therefore, free beta-hCG can be used effectively in a screening program for Down's syndrome; however, further studies are required to ascertain whether the measurement of free beta-hCG has any advantages over the use of total hCG for detecting Down's syndrome.     

Hyperglycosylated human chorionic gonadotropin (invasive trophoblast antigen) immunoassay: A new basis for gestational Down syndrome screening

BACKGROUND: Serum human chorionic gonadotropin (hCG) and hCG free beta-subunit tests are used in combination with unconjugated estriol and alpha-fetoprotein in the triple screen test, and with the addition of inhibin-A in the quadruple marker test for detecting Down syndrome in the second trimester of pregnancy. These tests have a limited detection rate for Down syndrome: approximately 40% for hCG or free beta-subunit alone, approximately 60% for the triple screen test, and approximately 70% for the quadruple marker test, all at 5%, or a relatively high, false-positive rate. New tests are needed with higher detection and lower false rates. Hyperglycosylated hCG (also known as invasive trophoblast antigen or ITA) is a new test. It specifically detects a unique oligosaccharide variant of hCG associated with Down syndrome pregnancies. We evaluated this new Down syndrome-directed test in prenatal diagnosis. METHODS: Hyperglycosylated hCG was measured in urine samples from women undergoing amniocentesis for advanced maternal age concerns at 14-22 weeks of gestation, 1448 with normal karyotype and 39 with Down syndrome fetuses. RESULTS: The median hyperglycosylated hCG value was 9.5-fold higher in Down syndrome cases (9.5 multiples of the normal karyotype median). The single test detected 80% of Down syndrome cases at a 5% false-positive rate. Urine hyperglycosylated hCG was combined with urine beta-core fragment (urine breakdown product of serum hCG free beta-subunit), serum alpha-fetoprotein, and maternal age-related risk. This urine-serum combination detected 96% of Down syndrome cases at a 5% false-positive rate, 94% of cases at a 3% false-positive rate, and 71% of cases at a 1% false-positive rate. These detection rates exceed those of any previously reported combination of biochemical markers. CONCLUSIONS: Hyperglycosylated hCG is a new base marker for Down syndrome screening in the second trimester of pregnancy. The measurement of hyperglycosylated hCG can fundamentally improve the performance of Down syndrome screening protocols.     

Cross-reaction with luteinizing hormone beta-core is responsible for the age-dependent increase of immunoreactive beta-core fragment of human chorionic gonadotropin in women with nonmalignant conditions

BACKGROUND: The beta-core fragment of human chorionic gonadotropin (hCGbetacf), also termed "beta-core" and urinary gonadotropin peptide (UGP), has been reported to be present in the urine of healthy women and to increase in concentration after menopause. This could reflect cross-reaction with the equivalent metabolite of luteinizing hormone (LH), the beta-LH-core. METHODS: We measured immunoreactive LH, hCG, free alpha-subunit, and free beta-subunit hCG (hCGbeta), as well as beta-core, using the S504 RIA and Triton UGP enzyme immunoassay in 274 urine samples from women with nonmalignant gynecological conditions. The molar cross-reaction of each assay with purified beta-LH-core was determined. RESULTS: Cross-reaction with beta-LH-core was 100% in the LH and the S504 beta-core assay, 5% in the Triton UGP assay, and <0.1% in the hCG, free alpha-subunit, and free hCGbeta assays. Median urine concentrations of all analytes showed an age-dependent increase. LH and free alpha-subunit concentrations were approximately 10(3) pmol/mol creatinine; hCG and S504 beta-core were approximately 10(2) pmol/mol creatinine; free hCGbeta and Triton UGP beta-core were in the tens of pmol/mol creatinine. The S504 beta-core concentrations were 10% of those of LH. S504 beta-core was strongly correlated with LH, but not with hCG or with free hCGbeta (LH, r2 = 0.45; hCG, r2 = 0.26; free hCGbeta, r2 = 0.03). The concentrations of beta-core detected by the Triton UGP assay, which has a 5% cross-reaction with beta-LH-core, were 2% of LH and 5% of the S504 beta-core concentrations. Triton UGP values correlated strongly with LH concentrations, but less well with S504 beta-core, intact hCG, and free hCGbeta (LH, r2 = 0.44; S504 beta-core, r2 = 0.33; hCG, r2 = 0.32; free hCGbeta, r2 = 0.19). CONCLUSIONS: Immunoreactive beta-core in women free of malignancies reflects cross-reaction with concentrations of the metabolite of LH, beta-LH-core, within the health-related reference interval.Copyright 1999 American Association for Clinical Chemistry     

Highly sensitive qualitative methods for serum choriogonadotropin (hCG): clinical specificity studies

We screened six highly sensitive kits, designed for serum pregnancy tests, for false-positive results. The two best were then evaluated more extensively. The "BETA-hCG MAIA-clone" (I) and the "TANDEM ICON" (II) kits gave only negative results for 100 sera from men at 5, 10, and 25 int. units/L (1st IRP). Of 100 serum specimens from post-menopausal women three and 10 were hCG positive by the II and the I reagents, respectively, but only at the 5 int. units (1st IRP) of hCG per liter level of sensitivity. At 10 and 25 int. units/L, all specimens were negative by both tests. The manufacturers of these kits recommend pregnancy testing only at the 25 int. units/L level of analytical sensitivity. By quantitative methods, hCG concentrations in the II positive samples ranged from 6 to 20 int. units/L (1st IRP) and lutropin concentrations were between 130 to greater than 150 int. units/L. The medical records of the corresponding patients did not support the presence of trophoblast or any other hCG-secreting tissues. During 15 months of routine use of the II reagents at an analytical sensitivity of 25 int. units/L (1st IRP) hCG for pregnancy testing (greater than 4000 serum specimens from pre-menopausal women), the staff has not reported to us any suspected false-positive findings.     

Concentrations of human choriogonadotropin, its beta-subunit, and the core fragment of the beta-subunit in serum and urine of men and nonpregnant women.

Sensitive, specific time-resolved immunofluorometric assays were used to measure the concentrations of human choriogonadotropin (hCG), free beta-subunit (beta-hCG), and the core fragment of beta-hCG (c beta-hCG) in serum and urine of men and nonpregnant women without evidence of cancer. Concentrations of hCG and beta-hCG were measurable in 59-70% of serum samples and in 50-59% of urine samples. c beta-hCG was mostly undetectable in serum but measurable in 81% of urine samples. Concentrations were higher in women than in men, and hCG concentrations increased with age. Therefore, reference ranges based on the 97.5 percentile were calculated separately for women and men and for those < 50 and > 50 years. However, concentrations of hCG correlated much more strongly with those of follicle-stimulating hormone than with age. hCG concentrations in serum were similar to those reported before, but beta-hCG concentrations were below the detection limit of earlier assays, and the upper reference limit was one-fifth to one-tenth the cutoff concentrations used earlier. In urine, hCG and c beta-hCG were the major forms of hCG, and their concentrations were similar to those of hCG in serum.     

Chronic ectopic pregnancy--two cases of acute rupture despite negative beta hCG

We present the cases of two women with chronic ectopic pregnancies who presented with acute tubal rupture and hemoperitoneum despite negative beta-human chorionic gonadotropin (beta hCG) pregnancy tests. The appropriate screening use of beta hCG assays to ascertain pregnancy status, the mechanisms by which ectopic pregnancy may be seen with negative beta hCG tests, and the limitations of various assays are discussed. One patient, not initially believed to be pregnant, underwent computed tomography (CT) scan. Experience with use of CT scan in ectopic pregnancy diagnosis is limited; our case illustrates some of the possible CT scan findings. These cases illustrate the potential for ectopic pregnancy to rupture with low, if not undetectable beta hCG hormone levels, and consequently why it is not recommended to rely on quantitative beta hCG levels to guide the decision to proceed with ultrasound imaging.     

Human chorionic gonadotropin isoforms in the diagnosis of ectopic pregnancy

BACKGROUND: Early diagnosis of ectopic pregnancy uses ultrasound with serial measurements of total human chorionic gonadotropin (hCG). The objective of this study was to explore the possibility that an isolated measurement of hCG isoforms/subunits rather than total hCG could be used as a single test for ectopic pregnancy. METHODS: Total and intact hCG, free hCG beta- and alpha-subunits (hCGbeta and -alpha), and hCG beta-core fragment were measured by RIA and IRMA in the serum and urine of 76 women presenting at outpatient emergency departments with a positive pregnancy test, lower abdominal pain, and/or vaginal bleeding. Final diagnoses were based on outcomes of pregnancies and tissue histology. RESULTS: Twenty-seven of the 76 women were subsequently diagnosed with viable pregnancies, 37 with spontaneous miscarriage, and 12 with ectopic pregnancy. Concentrations of all forms of hCG were lower in cases of ectopic pregnancy and spontaneous miscarriage than in viable pregnancies. Serum samples gave better results than urine samples. The free hCGbeta isoform (P <0.0001) had 100% sensitivity at a specificity of 79% at a 281 pmol/L (6.5 micro g/L) cutoff. Total hCG (P = 0.005) had comparable ROC characteristics with a 100% sensitivity and 68% specificity at a cutoff value of 1053 pmol/L (375 IU/L). Neither hCGbeta (P = 0.7) nor total hCG (P = 0.4) could distinguish ectopic pregnancies from spontaneous miscarriage. CONCLUSION: Measurement of serum free hCGbeta at the time of presentation can identify women with a high probability of ectopic pregnancy who may benefit from closer surveillance, reducing the risk of tubal rupture.