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Background hCG
Background hCG Laurence A. Cole USA hCG Reference Service, Angel Fire, NM, USA
36
Background hCG is one of the poorest studied scopes of hCG research, but it is still important. Only by knowing what the true background levels of female hCG are can we fairly say what concentration of serum and urine hCG constitutes a pregnancy or the successful treatment of gestational trophoblastic disease or other disorder. We understand that hCG is primarily produced by trophoblast cells during pregnancy. However, it is understood from false-positive total hCG results that background hCG can be produced by the pituitary gland as part of the menstrual cycle. It is also understood from cancer studies that hCG and its variants are also produced by malignancies. Furthermore, recent studies show hCG variant production by genetic disorders like familial hCG syndrome [1,2]. Other sources of positive hCG tests include false-positive hCG tests, quiescent gestational trophoblastic disease, and gestational trophoblastic diseases (see Chapter 28) [3,4]. What is the background serum hCG due to pituitary menstrual cycle production? The definition of acceptable background according to the Clinical Chemistry Society is a concentration corresponding to 97.5th percentile. As shown by Snyder et al. [5], examining 240 serum samples, the 97.5th percentile is 2.5 mIU/ml hCG (Table 36.1). In our own study of 797 menstrual cycle serum samples, we calculated a similar 97.5th percentile of 2.7 mIU/ml [6] (Table 36.1). These 97.5th percentiles indicate that any total hCG more than 2.7 mIU/ml can be considered as positive or indicating pregnancy. Currently, 5 mIU/ml is generally accepted as the cutoff in a serum hCG pregnancy test. More extensive studies have been performed with urine samples [7]. I have tested 9123 urine samples from the follicular phase, ovulatory phase, and luteal phase of the menstrual cycle (399 women followed-up daily for five menstrual cycles)[7]. As shown in Table 36.2, 2.8% or 1 in 259 of 9123 urine samples were elevated when tested with the Siemens Immulite total hCG pregnancy test or .1.0 mIU/ml. This created a 97.5th percentile for urine hCG of 1.0 mIU/ml. The 97.5th percentile is lower in urine than in serum. Over-the-counter pregnancy tests are available, such as First Response manual, with sensitivity as low as 3.5 mIU/ml. Examining the urine samples closer (Table 36.2), 31 of 3662 follicular phase urine samples (0.80%) and 206 of 2289 ovulatory phase urine samples are positive (9.0%), and 22 of 3172 luteal phase urine samples are positive (0.69%). Clearly, hCG is most commonly positive in the ovulatory phase. Gonadotropin-releasing hormone (GnRH) pulses reach a peak with the LH peak. It is thought that pituitary hCG production is incidental to the GnRH peak [7]. On the single day of the LH peak in each case, a total of 312 urine samples were Human Chorionic Gonadotropin (hCG). DOI: http://dx.doi.org/10.1016/B978-0-12-800749-5.00036-5 © 2015 Elsevier Inc. All rights reserved.
386
Human Chorionic Gonadotropin (hCG)
Table 36.1 Detection of hCG in serum during the menstrual cycle
Snyder et al., 2005 [5] Cole et al., 2009 [3]
Table 36.2
n
Clinical chemistry background limitation (97.5 centile)
240 797
2.5 mIU/ml 2.7 mIU/ml
Detection of hCG in urine during the menstrual period
Number of urines tested Number with hCG .1 mIU/ml Percentage positive Range of hCG detection 97.5th percentile
Follicular phase 1 10 days
Ovulatory phase 11 17 days
Luteal phase 18 28 days
Overall 1 28 days
3662
2289
3172
9123
31
206
22
259
0.80%
9.0%
0.69%
2.8%
1 4 mIU/ml
1 9.3 mIU/ml
1 2.7 mIU/ml
1 9.3 mIU/ml
,1 mIU/ml
1.6 mIU/ml
,1 mIU/ml
1.0 mIU/ml
collected. Of these, 107 (34%) were elevated ( .1.0 mIU/ml). The elevated urines ranged from 1 to 9.3 mIU/ml. It would appear from this finding that one in three women may have a false-positive hCG pregnancy test on the day of LH peak. Women need to be cautious of hCG pregnancy tests at approximately day 13 16 of the menstrual cycle or at the time of the LH peak. Considering pituitary hCG as the principal source of false-positive hCG tests, serum tests should has a pregnancy cutoff of .2.7 mIU/ml and urine pregnancy tests should have a cutoff of .1.0 mIU/ml. Other sources of false-positive tests need to be considered. These might include perimenopausal and postmenopausal women, cancer, and genetic disorders such as familial hCG syndrome [1,2,5 7]. Figure 36.1 shows the distribution of serum hCG in 103 perimenopause and postmenopause cases. As shown, hCG varies from ,1 to 39 mIU/ml. This figure might be a little biased in that it only shows problem cases referred to the USA hCG Reference Service. How can we include perimenopausal and postmenopausal women in our sensitivity statistics? If we estimate that 5% of these women are tested for pregnancy, then we can estimate that it increases the 97.5th percentile to 9.6 mIU/ml, or dramatically takes away the sensitivity of pregnancy tests. It is inferred that we cannot include perimenopausal and postmenopausal cases and, similarly, cancer cases and genetic disorder cases in our background hCG statistics. Perimenopausal and postmenopausal women need to be excluded from hCG pregnancy testing. This can be done by considering age older than 40 years or
Background hCG
387
Figure 36.1 Postmenopausal hCG in 103 women referred to the USA hCG Reference Service.
considering the results of a follicle stimulating hormone test ( .30 mIU/ml). Similarly, cancer cases need to be excluded from routine pregnancy screening. As shown in Chapter 20, 30% of individuals with cancer may have a positive result on a total hCG test. In cancer cases, the malignancy diagnosis should be enough reason to exclude them. In contrast, cases of familial hCG syndrome create a problem. This is a genetic disorder that may be difficult to diagnose [1,2]. However, we have no data yet regarding the incidence of this syndrome. We know it is a rare syndrome, and therefore we cannot calculate the effect it may have on background false-positives.
References [1] Cole LA. Familial hCG. J Reprod Immunol 2012;93:52 7. [2] Cole LA, Laidler LL. Inherited hCG. J Reprod Med 2010;55:99 102. [3] Cole LA, Laidler L, Muller C. USA hCG reference service, 10 year report. Clin Biochem 2010;43:1013 22. [4] Cole LA. Hyperglycosylated hCG, the most valuable test in the management of gestational trophoblastic neoplasms. Troph Dis Upd 2010;10:5 22. [5] Snyder JA, Haymond S, Parvin CA, Gonowski AM, Grenache DG. Diagnostic considerations in the measurement of human chorionic gonadotropin in aging woman. Clin Chem 2005;51:1830 5. [6] Cole LA. Background hCG in healthy non-pregnant women. Clin Chem 2005;51:1765 6. [7] Cole LA, Ladner DG. Background hCG in non-pregnant individuals: need for more sensitive point-of-care and over-the-counter pregnancy tests. Clin Biochem 2009;42:168 75.
36
Background hCG is one of the poorest studied scopes of hCG research, but it is still important. Only by knowing what the true background levels of female hCG are can we fairly say what concentration of serum and urine hCG constitutes a pregnancy or the successful treatment of gestational trophoblastic disease or other disorder. We understand that hCG is primarily produced by trophoblast cells during pregnancy. However, it is understood from false-positive total hCG results that background hCG can be produced by the pituitary gland as part of the menstrual cycle. It is also understood from cancer studies that hCG and its variants are also produced by malignancies. Furthermore, recent studies show hCG variant production by genetic disorders like familial hCG syndrome [1,2]. Other sources of positive hCG tests include false-positive hCG tests, quiescent gestational trophoblastic disease, and gestational trophoblastic diseases (see Chapter 28) [3,4]. What is the background serum hCG due to pituitary menstrual cycle production? The definition of acceptable background according to the Clinical Chemistry Society is a concentration corresponding to 97.5th percentile. As shown by Snyder et al. [5], examining 240 serum samples, the 97.5th percentile is 2.5 mIU/ml hCG (Table 36.1). In our own study of 797 menstrual cycle serum samples, we calculated a similar 97.5th percentile of 2.7 mIU/ml [6] (Table 36.1). These 97.5th percentiles indicate that any total hCG more than 2.7 mIU/ml can be considered as positive or indicating pregnancy. Currently, 5 mIU/ml is generally accepted as the cutoff in a serum hCG pregnancy test. More extensive studies have been performed with urine samples [7]. I have tested 9123 urine samples from the follicular phase, ovulatory phase, and luteal phase of the menstrual cycle (399 women followed-up daily for five menstrual cycles)[7]. As shown in Table 36.2, 2.8% or 1 in 259 of 9123 urine samples were elevated when tested with the Siemens Immulite total hCG pregnancy test or .1.0 mIU/ml. This created a 97.5th percentile for urine hCG of 1.0 mIU/ml. The 97.5th percentile is lower in urine than in serum. Over-the-counter pregnancy tests are available, such as First Response manual, with sensitivity as low as 3.5 mIU/ml. Examining the urine samples closer (Table 36.2), 31 of 3662 follicular phase urine samples (0.80%) and 206 of 2289 ovulatory phase urine samples are positive (9.0%), and 22 of 3172 luteal phase urine samples are positive (0.69%). Clearly, hCG is most commonly positive in the ovulatory phase. Gonadotropin-releasing hormone (GnRH) pulses reach a peak with the LH peak. It is thought that pituitary hCG production is incidental to the GnRH peak [7]. On the single day of the LH peak in each case, a total of 312 urine samples were Human Chorionic Gonadotropin (hCG). DOI: http://dx.doi.org/10.1016/B978-0-12-800749-5.00036-5 © 2015 Elsevier Inc. All rights reserved.
386
Human Chorionic Gonadotropin (hCG)
Table 36.1 Detection of hCG in serum during the menstrual cycle
Snyder et al., 2005 [5] Cole et al., 2009 [3]
Table 36.2
n
Clinical chemistry background limitation (97.5 centile)
240 797
2.5 mIU/ml 2.7 mIU/ml
Detection of hCG in urine during the menstrual period
Number of urines tested Number with hCG .1 mIU/ml Percentage positive Range of hCG detection 97.5th percentile
Follicular phase 1 10 days
Ovulatory phase 11 17 days
Luteal phase 18 28 days
Overall 1 28 days
3662
2289
3172
9123
31
206
22
259
0.80%
9.0%
0.69%
2.8%
1 4 mIU/ml
1 9.3 mIU/ml
1 2.7 mIU/ml
1 9.3 mIU/ml
,1 mIU/ml
1.6 mIU/ml
,1 mIU/ml
1.0 mIU/ml
collected. Of these, 107 (34%) were elevated ( .1.0 mIU/ml). The elevated urines ranged from 1 to 9.3 mIU/ml. It would appear from this finding that one in three women may have a false-positive hCG pregnancy test on the day of LH peak. Women need to be cautious of hCG pregnancy tests at approximately day 13 16 of the menstrual cycle or at the time of the LH peak. Considering pituitary hCG as the principal source of false-positive hCG tests, serum tests should has a pregnancy cutoff of .2.7 mIU/ml and urine pregnancy tests should have a cutoff of .1.0 mIU/ml. Other sources of false-positive tests need to be considered. These might include perimenopausal and postmenopausal women, cancer, and genetic disorders such as familial hCG syndrome [1,2,5 7]. Figure 36.1 shows the distribution of serum hCG in 103 perimenopause and postmenopause cases. As shown, hCG varies from ,1 to 39 mIU/ml. This figure might be a little biased in that it only shows problem cases referred to the USA hCG Reference Service. How can we include perimenopausal and postmenopausal women in our sensitivity statistics? If we estimate that 5% of these women are tested for pregnancy, then we can estimate that it increases the 97.5th percentile to 9.6 mIU/ml, or dramatically takes away the sensitivity of pregnancy tests. It is inferred that we cannot include perimenopausal and postmenopausal cases and, similarly, cancer cases and genetic disorder cases in our background hCG statistics. Perimenopausal and postmenopausal women need to be excluded from hCG pregnancy testing. This can be done by considering age older than 40 years or
Background hCG
387
Figure 36.1 Postmenopausal hCG in 103 women referred to the USA hCG Reference Service.
considering the results of a follicle stimulating hormone test ( .30 mIU/ml). Similarly, cancer cases need to be excluded from routine pregnancy screening. As shown in Chapter 20, 30% of individuals with cancer may have a positive result on a total hCG test. In cancer cases, the malignancy diagnosis should be enough reason to exclude them. In contrast, cases of familial hCG syndrome create a problem. This is a genetic disorder that may be difficult to diagnose [1,2]. However, we have no data yet regarding the incidence of this syndrome. We know it is a rare syndrome, and therefore we cannot calculate the effect it may have on background false-positives.
References [1] Cole LA. Familial hCG. J Reprod Immunol 2012;93:52 7. [2] Cole LA, Laidler LL. Inherited hCG. J Reprod Med 2010;55:99 102. [3] Cole LA, Laidler L, Muller C. USA hCG reference service, 10 year report. Clin Biochem 2010;43:1013 22. [4] Cole LA. Hyperglycosylated hCG, the most valuable test in the management of gestational trophoblastic neoplasms. Troph Dis Upd 2010;10:5 22. [5] Snyder JA, Haymond S, Parvin CA, Gonowski AM, Grenache DG. Diagnostic considerations in the measurement of human chorionic gonadotropin in aging woman. Clin Chem 2005;51:1830 5. [6] Cole LA. Background hCG in healthy non-pregnant women. Clin Chem 2005;51:1765 6. [7] Cole LA, Ladner DG. Background hCG in non-pregnant individuals: need for more sensitive point-of-care and over-the-counter pregnancy tests. Clin Biochem 2009;42:168 75.