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Human chorionic gonadotropin discriminatory zone in ectopic pregnancy: does assay harmonization matter?
ORIGINAL ARTICLE: EARLY PREGNANCY
Human chorionic gonadotropin discriminatory zone in ectopic pregnancy: does assay harmonization matter? Diana Desai, M.D.,a Jun Lu, M.S.,b Sara P. Wyness, B.S.,b Dina N. Greene, Ph.D.,c Kalen N. Olson, Ph.D.,d Carmen L. Wiley, Ph.D.,e and David G. Grenache, Ph.D.a,b a Department of Pathology, University of Utah School of Medicine, and b ARUP Institute for Clinical and Experimental Pathology, ARUP Laboratories, Salt Lake City, Utah; c Northern California Kaiser Permanente Regional Laboratory, Berkeley, California; d HealthPartners/Regions Hospital, St. Paul, Minnesota; and e PAML, Spokane, Washington
Objective: To determine the effect that lack of hCG assay harmonization has on the interpretation of a serum hCG concentration with regards to the hCG discriminatory zone. Design: A multisite method comparison study. Setting: Clinical laboratories. Patient(s): Eighty serum samples containing various concentrations of hCG. Intervention(s): None. Main Outcome Measure(s): Concentrations of hCG obtained from seven hCG reagent platforms. Result(s): The hCG concentrations were significantly different across hCG reagent platforms. Seventy-one percent of assay pairs showed significant differences with samples selected based on hCG concentrations between 1,500 and 3,500 IU/L as determined by a comparative method. Relative to the comparative method, the calculated hCG discriminatory zones for five assays were within 9%, and one assay was within 40% of the target concentrations of 1,500 and 3,500 IU/L. Conclusion(s): Despite significant differences in hCG concentrations across hCG immunoassays, an hCG concentration within a discriminatory zone of 1,500–3,500 IU/L can be used for all but one commonly used hCG reUse your smartphone agent platform. (Fertil SterilÒ 2014;-:-–-. Ó2014 by American Society for Reproductive to scan this QR code Medicine.) and connect to the Key Words: Ectopic pregnancy, hCG, hCG discriminatory zone, harmonization Discuss: You can discuss this article with its authors and with other ASRM members at http:// fertstertforum.com/desaid-human-chorionic-gonadotropin-discriminatory-ectopicassay-harmonization/
E
ctopic pregnancy is a potentially life-threatening complication of pregnancy in which the embryo implants outside the uterine cavity, most commonly in the fallopian tube. It frequently presents as abdominal pain and may result in vaginal bleeding. The incidence of ectopic preg-
nancy is approximately 2% of all pregnancies, and it is the leading cause of maternal mortality in the first trimester (1). Consequently, prompt and accurate diagnosis of an ectopic pregnancy is of high importance. Diagnosis of an ectopic pregnancy requires the exclusion of a normal, in-
Received December 8, 2013; revised January 19, 2014; accepted February 11, 2014. D.G.G. reports personal fees from Abbott Point of Care, Inc. D.D. has nothing to disclose. J.L. has nothing to disclose. S.P.W. has nothing to disclose. D.N.G. has nothing to disclose. K.N.O. has nothing to disclose. C.L.W. has nothing to disclose. Reprint requests: David G. Grenache, Ph.D., Department of Pathology, University of Utah, c/o ARUP Laboratories, 500 Chipeta Way, Salt Lake City, Utah 84108 (E-mail: [email protected]. edu). Fertility and Sterility® Vol. -, No. -, - 2014 0015-0282/$36.00 Copyright ©2014 American Society for Reproductive Medicine, Published by Elsevier Inc. http://dx.doi.org/10.1016/j.fertnstert.2014.02.023 VOL. - NO. - / - 2014
discussion forum for this article now.*
* Download a free QR code scanner by searching for “QR scanner” in your smartphone’s app store or app marketplace.
trauterine pregnancy and is facilitated by the use of transvaginal ultrasound (TVUS) to visualize the location of the yolk sac or embryo. If present, an intrauterine pregnancy should be evident by TVUS at R42 days of gestation (1). However, such precise dating is often not available for patients who present with symptoms of ectopic pregnancy and a nondiagnostic TVUS. For these patients, the concentration of serum hCG is used as a surrogate marker for gestational age and is commonly interpreted against the ‘‘hCG discriminatory zone,’’ the concentration of hCG at which the sensitivity of TVUS for detecting an 1
ORIGINAL ARTICLE: EARLY PREGNANCY this study was to determine the effect that the lack of hCG assay harmonization has on the interpretation of an hCG result with regards to the hCG discriminatory zone.
FIGURE 1
MATERIALS AND METHODS
Box and whisker plot of hCG results from 80 serum samples tested on seven commercially available hCG platforms. The whiskers represent the minimum and maximum hCG result, and the horizontal bar in the box represents the median. The dashed lines represent the hCG discriminatory zone of 1,500–3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
intrauterine gestation is nearly 100% (1). The absence of an intrauterine gestation when the hCG concentration exceeds the discriminatory zone suggests that the pregnancy is not viable, but it is not diagnostic of an ectopic pregnancy (2). The hCG discriminatory zone is commonly described as an hCG cutoff concentration between 1,500 and either 2,000, 2,500 or 3,000 IU/L. Guidelines from the American College of Obstetricians and Gynecologists define it as 1,500– 2,000 IU/L (3). Importantly, quantitative hCG assays are not harmonized, meaning that hCG results from different reagent platforms can yield different results when the same sample is tested. Clinical practice guidelines that recommend specific analyte concentrations as decision thresholds often fail to address the effect that the lack of harmonization can have on result interpretation. The objective of
Deidentified, residual serum samples sent to ARUP Laboratories for hCG testing were used for this study with approval from the University of Utah Institutional Review Board. Samples were selected based on hCG concentration and were used to create, by pooling if necessary, 80 discrete specimens. By design, 25% of the samples were created to target an hCG concentration <1,000 IU/L, 50% with an hCG concentration between 1,000 and 4,000 IU/L, and 25% with an hCG concentration of >4,000 IU/L. After preparation, 0.5 mL aliquots were prepared and the samples stored at 20 C or colder until they were tested up to 7 days later. The concentration of hCG in each sample was determined using each of the following commercially available hCG assays: ARCHITECT Total b-hCG (Abbott Diagnostics), DxI Total hCG (Beckman Coulter Diagnostics), E170 hCGþb (Roche Diagnostics), Centaur Total hCG (Siemens Healthcare Diagnostics), Dimension hCG (Siemens Healthcare Diagnostics), IMMULITE hCG (Siemens Healthcare Diagnostics), and Vitros 5600 b-hCG (Ortho Clinical Diagnostics). Each of these assays recognizes intact hCG and several hCG variants with no cross-reactivity with other glycoprotein hormones. Across all assays, coefficients of variation ranged from a low of 2.3% at 1,780 IU/L to 5.5% at 365 IU/L. A minimum of two quality-control materials were evaluated before sample testing to verify acceptable analytical performance. Statistical analysis was performed using nonparametric repeated measures analysis of variance followed by post hoc testing to compare pairs of group means (n ¼ 21 pairs). Deming regression was used to define the relationship between each assay and the comparative method. The Roche E170 assay was selected as the comparative method because it detects all clinically relevant forms of serum hCG with equimolar detection (4, 5). Statistical analyses were performed using Prism (version 5, GraphPad Software).
TABLE 1 Post hoc testing after nonparametric repeated measures analysis of variance to compare group means from serum samples tested on seven commercially available hCG platforms. Abbott Architect Beckman DxI Siemens Centaur Siemens Dimension Siemens Immulite Ortho Vitros Roche E170 Beckman DxI Siemens Centaur Siemens Dimension Siemens Immulite Ortho Vitros Roche E170
<0.05 <0.05 <0.05 <0.05 <0.05 <0.05
<0.05 <0.05a <0.05 NS NS
<0.05 <0.05 <0.05 <0.05
NSb NS NS
<0.05 <0.05
NS
Note: See text for the name of the hCG assay used on each platform. NS ¼ not significant. a This pair was not significantly different using 43 serum samples selected on the basis of an hCG concentration between 1,500 and 3,500 IU/L as determined by the comparative method. b This pair was significantly different (P< .05) using 43 serum samples selected on the basis of an hCG concentration between 1,500 and 3,500 IU/L as determined by the comparative method. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
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Fertility and Sterility® of >1.0 (range, 1.006–1.431) for all methods except for Siemens IMMULITE (0.911). When the upper and lower limits of the hCG discriminatory zone were calculated from the regression equation for the other six methods, all but the Siemens Centaur assay were within 9% of the frequently cited cutoffs of 1,500 and 3,500 IU/L relative to the comparative method (Table 2). Results from the Siemens Centaur assay were 35% and 40% higher at the same cutoffs, respectively, which translates to an hCG concentration range of 2,020– 4,882 IU/L (Table 2).
FIGURE 2
DISCUSSION
Box and whisker plot of hCG results from 43 serum samples selected on the basis of a concentration between 1,500 and 3,500 IU/L as determined by the Roche E170 and tested on seven commercially available hCG platforms. The whiskers represent the minimum and maximum hCG result, and the horizontal bar in the box represents the median. The dashed lines represent the hCG discriminatory zone of 1,500–3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
RESULTS Measured hCG concentrations in all 80 samples across all seven assays ranged from 74 to 6,660 IU/L (Fig. 1). The hCG results were significantly different across all platforms evaluated (P< .0001). Post hoc testing revealed that hCG results were significantly different for 71% (15/21) of assay pairs (P< .05; Table 1). Similar results were observed when samples were selected based on hCG concentrations between 1,500 and 3,500 IU/L as determined by the comparative method (n ¼ 43; Fig. 2). Post hoc testing of this data set revealed that hCG results were still significantly different for 71% (15/21) of assay pairs (P< .05), but the assay pairs showing significant differences were slightly different from those in the complete data set (Table 1). Deming regression analyses of all samples using the Roche E170 assay as the comparative method produced slopes
The timely diagnosis of an ectopic pregnancy is imperative because the presence of this potentially life-threatening condition guides appropriate clinical management. An intrauterine pregnancy must be excluded before an ectopic pregnancy diagnosis. Although a viable intrauterine pregnancy should be detected by TVUS at R42 days of gestation, such precise dating is often not known at presentation. In this circumstance, the concentration of serum hCG can be used as a surrogate for gestational age when interpreted in the context of the hCG discriminatory zone. Diagnostic algorithms that integrate history, clinical examination, TVUS, and hCG concentrations have been described (6). However, models in which absolute hCG concentrations form the basis for diagnosis may have limitations as they neglect to account for the lack of hCG assay harmonization. The effects that the lack of hCG assay harmonization may have on clinical decision making and patient care have not be described. Such evidence is needed, particularly when hCG concentrations are interpreted against recommended thresholds. Such is the case for the diagnosis of ectopic pregnancy due to the recommended use of the hCG discriminatory zone (3). Our data confirms the lack of harmonization among seven hCG assays. Using all 80 samples, hCG concentrations were significantly different between all but six of 21 assay pairs (Table 1). The same was true when hCG concentrations in a subset of 43 samples with an hCG concentration between 1,500 and 3,500 IU/L (as determined by the comparative method) were considered. Although there are academic efforts to encourage harmonization of hCG assays (7),
TABLE 2 Deming regression analysis of all samples for six commercially available hCG platforms compared with the comparative method. Roche E170 (comparative method) Slope Intercept Spearman r Discriminatory zone, IU/L Difference from 1,500 IU/L (%) Difference from 3,500 IU/L (%)
1.00 0.0 1.0 1,500–3,500 0.0 0.0
Abbott Architect
Siemens Centaur
Siemens Dimension
Beckman DxI
Siemens Immulite
Ortho Vitros
1.104 1.431 1.006 1.077 0.911 1.089 74.6 126.2 51.2 86.1 9.68 122.3 0.998 0.996 0.988 0.987 0.974 0.996 1,581–3,789 2,020–4,882 1,458–3,470 1,529–3,683 1,376–3,198 1,511–3,689 5.4 34.7 2.8 2.0 8.3 0.7 8.3 39.5 0.9 5.2 8.6 5.4
Note: Also shown is the hCG discriminatory zone for each assay determined from the regression equation and the relative differences from 1,500 and 3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
VOL. - NO. - / - 2014
3
ORIGINAL ARTICLE: EARLY PREGNANCY manufacturers have little incentive to comply, and therefore comparability of results between reagent platforms remains an obstacle. While best practice would require a clinician to establish an appropriate hCG discriminatory zone based on the hCG assay used in a given laboratory, our data suggest that this may not always be necessary. Despite the significant interassay disparity of serum hCG concentrations between the majority of evaluated platforms, the differences may not be clinically significant in their application to the interpretation of the hCG discriminatory zone. Relative to the comparative method, all of the assays except the Siemens Centaur assay were within 9% of the hCG concentrations that are frequently cited to encompass the hCG discriminatory zone. This suggests that an hCG discriminatory zone falling within this range can be applied to all platforms except the Siemens Centaur, for which a discriminatory zone of 2,000–4,900 IU/L would be estimated to produce equivalence. Acknowledgments: The authors thank Dr. Annu Khajuria and Mr. Bryan Robeson of the Lakeview Medical Center-
4
Marshfield Clinic for performing some of the hCG tests for this study.
REFERENCES 1. 2. 3. 4.
5.
6.
7.
Barnhart KT. Clinical practice. Ectopic pregnancy. N Engl J Med 2009;361: 379–87. Barnhart KT. Early pregnancy failure: beware of the pitfalls of modern management. Fertil Steril 2012;98:1061–5. ACOG. ACOG Practice Bulletin. Medical management of ectopic pregnancy. Obstet Gynecol 2008;111:1479–85. Whittington J, Fantz CR, Gronowski AM, McCudden CR, Mullins R, Sokoll L, et al. The analytical specificity of human chorionic gonadotropin assays determined using WHO International Reference Reagents. Clin Chim Acta 2010;411:81–5. Sturgeon CM, Berger P, Bidart J-M, Birken S, Burns C, Norman RJ, et al. Differences in recognition of the 1st WHO international reference reagents for hCG-related isoforms by diagnostic immunoassays for human chorionic gonadotropin. Clin Chem 2009;55:1484–91. van Mello NM, Mol F, Ankum WM, Mol BW, van der Veen F, Hajenius PJ. Ectopic pregnancy: how the diagnostic and therapeutic management has changed. Fertil Steril 2012;98:1066–73. Sturgeon CM, Ellis AR. Standardization of FSH, LH and hCG—current position and future prospects. Mol Cell Endocrinol 2007;260–262:301–9.
VOL. - NO. - / - 2014
Human chorionic gonadotropin discriminatory zone in ectopic pregnancy: does assay harmonization matter? Diana Desai, M.D.,a Jun Lu, M.S.,b Sara P. Wyness, B.S.,b Dina N. Greene, Ph.D.,c Kalen N. Olson, Ph.D.,d Carmen L. Wiley, Ph.D.,e and David G. Grenache, Ph.D.a,b a Department of Pathology, University of Utah School of Medicine, and b ARUP Institute for Clinical and Experimental Pathology, ARUP Laboratories, Salt Lake City, Utah; c Northern California Kaiser Permanente Regional Laboratory, Berkeley, California; d HealthPartners/Regions Hospital, St. Paul, Minnesota; and e PAML, Spokane, Washington
Objective: To determine the effect that lack of hCG assay harmonization has on the interpretation of a serum hCG concentration with regards to the hCG discriminatory zone. Design: A multisite method comparison study. Setting: Clinical laboratories. Patient(s): Eighty serum samples containing various concentrations of hCG. Intervention(s): None. Main Outcome Measure(s): Concentrations of hCG obtained from seven hCG reagent platforms. Result(s): The hCG concentrations were significantly different across hCG reagent platforms. Seventy-one percent of assay pairs showed significant differences with samples selected based on hCG concentrations between 1,500 and 3,500 IU/L as determined by a comparative method. Relative to the comparative method, the calculated hCG discriminatory zones for five assays were within 9%, and one assay was within 40% of the target concentrations of 1,500 and 3,500 IU/L. Conclusion(s): Despite significant differences in hCG concentrations across hCG immunoassays, an hCG concentration within a discriminatory zone of 1,500–3,500 IU/L can be used for all but one commonly used hCG reUse your smartphone agent platform. (Fertil SterilÒ 2014;-:-–-. Ó2014 by American Society for Reproductive to scan this QR code Medicine.) and connect to the Key Words: Ectopic pregnancy, hCG, hCG discriminatory zone, harmonization Discuss: You can discuss this article with its authors and with other ASRM members at http:// fertstertforum.com/desaid-human-chorionic-gonadotropin-discriminatory-ectopicassay-harmonization/
E
ctopic pregnancy is a potentially life-threatening complication of pregnancy in which the embryo implants outside the uterine cavity, most commonly in the fallopian tube. It frequently presents as abdominal pain and may result in vaginal bleeding. The incidence of ectopic preg-
nancy is approximately 2% of all pregnancies, and it is the leading cause of maternal mortality in the first trimester (1). Consequently, prompt and accurate diagnosis of an ectopic pregnancy is of high importance. Diagnosis of an ectopic pregnancy requires the exclusion of a normal, in-
Received December 8, 2013; revised January 19, 2014; accepted February 11, 2014. D.G.G. reports personal fees from Abbott Point of Care, Inc. D.D. has nothing to disclose. J.L. has nothing to disclose. S.P.W. has nothing to disclose. D.N.G. has nothing to disclose. K.N.O. has nothing to disclose. C.L.W. has nothing to disclose. Reprint requests: David G. Grenache, Ph.D., Department of Pathology, University of Utah, c/o ARUP Laboratories, 500 Chipeta Way, Salt Lake City, Utah 84108 (E-mail: [email protected]. edu). Fertility and Sterility® Vol. -, No. -, - 2014 0015-0282/$36.00 Copyright ©2014 American Society for Reproductive Medicine, Published by Elsevier Inc. http://dx.doi.org/10.1016/j.fertnstert.2014.02.023 VOL. - NO. - / - 2014
discussion forum for this article now.*
* Download a free QR code scanner by searching for “QR scanner” in your smartphone’s app store or app marketplace.
trauterine pregnancy and is facilitated by the use of transvaginal ultrasound (TVUS) to visualize the location of the yolk sac or embryo. If present, an intrauterine pregnancy should be evident by TVUS at R42 days of gestation (1). However, such precise dating is often not available for patients who present with symptoms of ectopic pregnancy and a nondiagnostic TVUS. For these patients, the concentration of serum hCG is used as a surrogate marker for gestational age and is commonly interpreted against the ‘‘hCG discriminatory zone,’’ the concentration of hCG at which the sensitivity of TVUS for detecting an 1
ORIGINAL ARTICLE: EARLY PREGNANCY this study was to determine the effect that the lack of hCG assay harmonization has on the interpretation of an hCG result with regards to the hCG discriminatory zone.
FIGURE 1
MATERIALS AND METHODS
Box and whisker plot of hCG results from 80 serum samples tested on seven commercially available hCG platforms. The whiskers represent the minimum and maximum hCG result, and the horizontal bar in the box represents the median. The dashed lines represent the hCG discriminatory zone of 1,500–3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
intrauterine gestation is nearly 100% (1). The absence of an intrauterine gestation when the hCG concentration exceeds the discriminatory zone suggests that the pregnancy is not viable, but it is not diagnostic of an ectopic pregnancy (2). The hCG discriminatory zone is commonly described as an hCG cutoff concentration between 1,500 and either 2,000, 2,500 or 3,000 IU/L. Guidelines from the American College of Obstetricians and Gynecologists define it as 1,500– 2,000 IU/L (3). Importantly, quantitative hCG assays are not harmonized, meaning that hCG results from different reagent platforms can yield different results when the same sample is tested. Clinical practice guidelines that recommend specific analyte concentrations as decision thresholds often fail to address the effect that the lack of harmonization can have on result interpretation. The objective of
Deidentified, residual serum samples sent to ARUP Laboratories for hCG testing were used for this study with approval from the University of Utah Institutional Review Board. Samples were selected based on hCG concentration and were used to create, by pooling if necessary, 80 discrete specimens. By design, 25% of the samples were created to target an hCG concentration <1,000 IU/L, 50% with an hCG concentration between 1,000 and 4,000 IU/L, and 25% with an hCG concentration of >4,000 IU/L. After preparation, 0.5 mL aliquots were prepared and the samples stored at 20 C or colder until they were tested up to 7 days later. The concentration of hCG in each sample was determined using each of the following commercially available hCG assays: ARCHITECT Total b-hCG (Abbott Diagnostics), DxI Total hCG (Beckman Coulter Diagnostics), E170 hCGþb (Roche Diagnostics), Centaur Total hCG (Siemens Healthcare Diagnostics), Dimension hCG (Siemens Healthcare Diagnostics), IMMULITE hCG (Siemens Healthcare Diagnostics), and Vitros 5600 b-hCG (Ortho Clinical Diagnostics). Each of these assays recognizes intact hCG and several hCG variants with no cross-reactivity with other glycoprotein hormones. Across all assays, coefficients of variation ranged from a low of 2.3% at 1,780 IU/L to 5.5% at 365 IU/L. A minimum of two quality-control materials were evaluated before sample testing to verify acceptable analytical performance. Statistical analysis was performed using nonparametric repeated measures analysis of variance followed by post hoc testing to compare pairs of group means (n ¼ 21 pairs). Deming regression was used to define the relationship between each assay and the comparative method. The Roche E170 assay was selected as the comparative method because it detects all clinically relevant forms of serum hCG with equimolar detection (4, 5). Statistical analyses were performed using Prism (version 5, GraphPad Software).
TABLE 1 Post hoc testing after nonparametric repeated measures analysis of variance to compare group means from serum samples tested on seven commercially available hCG platforms. Abbott Architect Beckman DxI Siemens Centaur Siemens Dimension Siemens Immulite Ortho Vitros Roche E170 Beckman DxI Siemens Centaur Siemens Dimension Siemens Immulite Ortho Vitros Roche E170
<0.05 <0.05 <0.05 <0.05 <0.05 <0.05
<0.05 <0.05a <0.05 NS NS
<0.05 <0.05 <0.05 <0.05
NSb NS NS
<0.05 <0.05
NS
Note: See text for the name of the hCG assay used on each platform. NS ¼ not significant. a This pair was not significantly different using 43 serum samples selected on the basis of an hCG concentration between 1,500 and 3,500 IU/L as determined by the comparative method. b This pair was significantly different (P< .05) using 43 serum samples selected on the basis of an hCG concentration between 1,500 and 3,500 IU/L as determined by the comparative method. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
2
VOL. - NO. - / - 2014
Fertility and Sterility® of >1.0 (range, 1.006–1.431) for all methods except for Siemens IMMULITE (0.911). When the upper and lower limits of the hCG discriminatory zone were calculated from the regression equation for the other six methods, all but the Siemens Centaur assay were within 9% of the frequently cited cutoffs of 1,500 and 3,500 IU/L relative to the comparative method (Table 2). Results from the Siemens Centaur assay were 35% and 40% higher at the same cutoffs, respectively, which translates to an hCG concentration range of 2,020– 4,882 IU/L (Table 2).
FIGURE 2
DISCUSSION
Box and whisker plot of hCG results from 43 serum samples selected on the basis of a concentration between 1,500 and 3,500 IU/L as determined by the Roche E170 and tested on seven commercially available hCG platforms. The whiskers represent the minimum and maximum hCG result, and the horizontal bar in the box represents the median. The dashed lines represent the hCG discriminatory zone of 1,500–3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
RESULTS Measured hCG concentrations in all 80 samples across all seven assays ranged from 74 to 6,660 IU/L (Fig. 1). The hCG results were significantly different across all platforms evaluated (P< .0001). Post hoc testing revealed that hCG results were significantly different for 71% (15/21) of assay pairs (P< .05; Table 1). Similar results were observed when samples were selected based on hCG concentrations between 1,500 and 3,500 IU/L as determined by the comparative method (n ¼ 43; Fig. 2). Post hoc testing of this data set revealed that hCG results were still significantly different for 71% (15/21) of assay pairs (P< .05), but the assay pairs showing significant differences were slightly different from those in the complete data set (Table 1). Deming regression analyses of all samples using the Roche E170 assay as the comparative method produced slopes
The timely diagnosis of an ectopic pregnancy is imperative because the presence of this potentially life-threatening condition guides appropriate clinical management. An intrauterine pregnancy must be excluded before an ectopic pregnancy diagnosis. Although a viable intrauterine pregnancy should be detected by TVUS at R42 days of gestation, such precise dating is often not known at presentation. In this circumstance, the concentration of serum hCG can be used as a surrogate for gestational age when interpreted in the context of the hCG discriminatory zone. Diagnostic algorithms that integrate history, clinical examination, TVUS, and hCG concentrations have been described (6). However, models in which absolute hCG concentrations form the basis for diagnosis may have limitations as they neglect to account for the lack of hCG assay harmonization. The effects that the lack of hCG assay harmonization may have on clinical decision making and patient care have not be described. Such evidence is needed, particularly when hCG concentrations are interpreted against recommended thresholds. Such is the case for the diagnosis of ectopic pregnancy due to the recommended use of the hCG discriminatory zone (3). Our data confirms the lack of harmonization among seven hCG assays. Using all 80 samples, hCG concentrations were significantly different between all but six of 21 assay pairs (Table 1). The same was true when hCG concentrations in a subset of 43 samples with an hCG concentration between 1,500 and 3,500 IU/L (as determined by the comparative method) were considered. Although there are academic efforts to encourage harmonization of hCG assays (7),
TABLE 2 Deming regression analysis of all samples for six commercially available hCG platforms compared with the comparative method. Roche E170 (comparative method) Slope Intercept Spearman r Discriminatory zone, IU/L Difference from 1,500 IU/L (%) Difference from 3,500 IU/L (%)
1.00 0.0 1.0 1,500–3,500 0.0 0.0
Abbott Architect
Siemens Centaur
Siemens Dimension
Beckman DxI
Siemens Immulite
Ortho Vitros
1.104 1.431 1.006 1.077 0.911 1.089 74.6 126.2 51.2 86.1 9.68 122.3 0.998 0.996 0.988 0.987 0.974 0.996 1,581–3,789 2,020–4,882 1,458–3,470 1,529–3,683 1,376–3,198 1,511–3,689 5.4 34.7 2.8 2.0 8.3 0.7 8.3 39.5 0.9 5.2 8.6 5.4
Note: Also shown is the hCG discriminatory zone for each assay determined from the regression equation and the relative differences from 1,500 and 3,500 IU/L. See text for the name of the hCG assay used on each platform. Desai. hCG discriminatory zone and assay harmonization. Fertil Steril 2014.
VOL. - NO. - / - 2014
3
ORIGINAL ARTICLE: EARLY PREGNANCY manufacturers have little incentive to comply, and therefore comparability of results between reagent platforms remains an obstacle. While best practice would require a clinician to establish an appropriate hCG discriminatory zone based on the hCG assay used in a given laboratory, our data suggest that this may not always be necessary. Despite the significant interassay disparity of serum hCG concentrations between the majority of evaluated platforms, the differences may not be clinically significant in their application to the interpretation of the hCG discriminatory zone. Relative to the comparative method, all of the assays except the Siemens Centaur assay were within 9% of the hCG concentrations that are frequently cited to encompass the hCG discriminatory zone. This suggests that an hCG discriminatory zone falling within this range can be applied to all platforms except the Siemens Centaur, for which a discriminatory zone of 2,000–4,900 IU/L would be estimated to produce equivalence. Acknowledgments: The authors thank Dr. Annu Khajuria and Mr. Bryan Robeson of the Lakeview Medical Center-
4
Marshfield Clinic for performing some of the hCG tests for this study.
REFERENCES 1. 2. 3. 4.
5.
6.
7.
Barnhart KT. Clinical practice. Ectopic pregnancy. N Engl J Med 2009;361: 379–87. Barnhart KT. Early pregnancy failure: beware of the pitfalls of modern management. Fertil Steril 2012;98:1061–5. ACOG. ACOG Practice Bulletin. Medical management of ectopic pregnancy. Obstet Gynecol 2008;111:1479–85. Whittington J, Fantz CR, Gronowski AM, McCudden CR, Mullins R, Sokoll L, et al. The analytical specificity of human chorionic gonadotropin assays determined using WHO International Reference Reagents. Clin Chim Acta 2010;411:81–5. Sturgeon CM, Berger P, Bidart J-M, Birken S, Burns C, Norman RJ, et al. Differences in recognition of the 1st WHO international reference reagents for hCG-related isoforms by diagnostic immunoassays for human chorionic gonadotropin. Clin Chem 2009;55:1484–91. van Mello NM, Mol F, Ankum WM, Mol BW, van der Veen F, Hajenius PJ. Ectopic pregnancy: how the diagnostic and therapeutic management has changed. Fertil Steril 2012;98:1066–73. Sturgeon CM, Ellis AR. Standardization of FSH, LH and hCG—current position and future prospects. Mol Cell Endocrinol 2007;260–262:301–9.
VOL. - NO. - / - 2014