In! J Gynaecol Obstet 17: 190-193, 1979
Current Status of Immunologic Pregnancy Tests Richard Derman, 1 David A. Edelman 2 and Gary S. Berger 3 3
Department of Obstetrics and Gynecology, Cornell University Medical Center, New York, New York, USA International Fertility Research Program, Research Triangle Park, North Carolina, USA University of North Carolina, Chapel Hill, North Carolina, USA
ABSTRACT Derman R, Edelman DA, Berger GS (Dept of Obstetrics and Gynecology, Cornell University Medical Center, New York, NY; International Fertility Research Program, Research Triangle Park, NC; and University of North Carolina, Chapel Hill, NC, USA). Current status of immunologic pregnancy tests. IntJ Gynaecol Obstet 17: 190-193, 1979 Information about the mechanism of various pregnancy tests is summarized. The sensitivity of these tests as well as their advantages and limitations in a clinical setting are presented and evaluated in an effort to maximize their usefulness in a clinical setting.
INTRODUCTION There are a variety of situations in which the ability to diagnose pregnancy early in gestation may be vital for both diagnoses and treatment. Although many pregnancy tests are available, there is often a lack of understanding of the mechanisms of the various tests, their sensitivity and specificity and their relative advantages and limitations. This report summarizes information about a variety of pregnancy tests in an effort to help maximize their usefulness in the clinical setting.
CATEGORIES A N D MECHANISMS T h e basis for almost all pregnancy tests is the detection of h u m a n chorionic gonadotropin (HCG) in urine or plasma. H C G is a glycoprotein produced by the placental trophoblastic cells. In the early gestational period, the H C G production in placental tissue doubles approximately every two days (6) until it reaches a peak at about the eighth week after the onset of the last normal menstrual period.
IntJ Gynaecol Obstet 17
Early pregnancy tests were qualitative in nature and were based on the biologic effects which resulted when the subject's urine was administered to an experimental animal (Table I). T h e common types of end points were luteinization of the mouse ovary, ovulation in the rabbit and sperm ejection in the frog. T h e sensitivity of these three tests was in the range of 10 IU of H C G / m l , which meant that the tests could be expected to reveal a positive result approximately 25 days after ovulation. Development of each successive test resulted in a reduction in the time required for performance and interpretation (approximately five days for the mouse test to two hours for the frog test). With the introduction of commercially available immunologic pregnancy tests in 1961, the prospect for early diagnosis of pregnancy became feasible in most clinical settings. T h e majority of immunoassays are based on the principle of indirect agglutination, either hemagglutination inhibition or latex particle inhibition, and can either be carried out in a test tube or on a slide. T h e tube tests are somewhat more sensitive (0.7-1.25 IU of H C G / m l for tube tests versus 1.0-3.5 IU of H C G / m l for slide tests), but require more time to perform (one-two hours versus two minutes). Even the slide tests (with a sensitivity of up to 3.5 IU of H C G / m l ) can, in theory, detect pregnancy within seven days of the missed menstrual period. Some of the immunologic tube and slide tests currently available are listed in T a b l e II. This table also shows the manufacturers' stated test sensitivity (ie, the minimum concentration of H C G that the test can detect) and the sensitivities based on an independent laboratory evaluation (3). In all cases, the manufacturers' stated sensitivities are lower than the actual ones. T h e manufacturers' stated sensitivities do, however, reflect the relative range of sensitivities for the different tests; the tube tests generally detect relatively lower concentrations of H C G than the slide tests.
Immunologic pregnancy tests
] 91
Table I. Historical development of pregnancy tests.
Test
Days After Ovulation Pregnancy Detectable
End Point
Testing Time
Biologic
Mouse-luteinization Rabbit-ovulation Frog sperm ejection
25 25 25
5 days 2 days 2 hr
Immunologic
Hemagglutination inhibition (tube test) Latex particle inhibition (tube test) Latex particle inhibition (slide test)
18-20
2 hr
18-20 25
1.5 hr 2 min
Radioassay
Competition with 1Z5 I-HCG for specific antibodies or receptors
6-12
1 - 2 4 hr
Table II. Sensitivities of selected immunologic pregnancy tests. 1 Pregnancy Tests Tube Tests Placentex Pregnosticon Accuspheres UCG Lyphotest
Manufacturer Roche Diagnostics 2 Organon 3 Wampole 4
Slide Tests Ortho 5 Gravindex Pregnosis Roche Diagnostics Organon Pregnosticon Dri-Dot Wampole UCG Slide 1 Data adapted from Reference 3. 2 Roche Diagnostics, Nutley, NJ, USA. 3 Organon Inc. West Orange, NJ, USA. 4 Wampole Laboratories, Cranbury, NJ, USA. 5 Ortho Diagnostics Inc, Rah tan, NJ, USA.
More sensitive than the immunologic pregnancy tests are the recently developed radioimmunoassays or radioreceptorassays which can detect plasma H C G levels of 0.5 IU of H C G / m l or less. Despite the increased sensitivity of these tests, they require specialized laboratory equipment and personnel and are not available in facilities where most pregnancy tests are performed.
ACCURACY T h e accuracy- of immunologic pregnancy tests depends upon several factors. First, the test material itself must be properly stored and the manufacturer's directions followed in performing and interpreting the test. T h e concentration of H C G in the urine or plasma is related to the duration a n d normality of the pregnancy and has a major effect on the accuracy of any test. T o determine test
Stated Sensitivity (IU of HCG/ml) 0.75-1.25 0.7-0.9 1.0 3.5 1.5-2.5 1-2 2.0
Actual Sensitivity (IU of HCG/ml) 1-2 1-3 4-6 4-14.5 2-6 3-10 4-15
accuracy, one must take into account "false-positive" readings (ie, tests read as positive when pregnancy does not exist) and "false-negative" readings (ie, tests read as negative when pregnancy does exist). T h e results from two studies that compared the percentages of correct positive test results for various immunologic slide tests performed on pregnant women at different stages of pregnancy amenorrhea are shown in Table III. For each duration of amenorrhea, there was no statistically significant difference (p > 0.10) in the percentage of correct positive test results in the two studies. In both studies, there was a statistically significant increase (p < 0.10) in the percentage of correct positive results with increasing length of amenorrhea. T h e small number of women at each duration of amenorrhea shown in Table III do not permit accurate evaluation of the correct positive (or false-negative) rates for each of the pregnancy tests. Although some studies cited in
IntJ Gynaecol Obstet 17
192
Dermtin el al
Table III. Percentage of correct test results obtained with four slide pregnancy tests performed on pregnant women in two studies. Days from Last Menstrual Period Study I1 41-51 N = 42
37-40 N = 9 %
Pregnancy Test Gravindex Pregnosis Pregnosticon Dri-Dot UCG Slide
88.9 88.9 77.8 77.8
Study II2
%
51-59 N = 24 %
40-69 N = 82
70-99 N = 42
83.3 95.2 83.3 90.5
95.8 95.8 95.8 100.0
92.7 97.6 93.9 92.7
92.9 92.9 92.9 90.5
%
%
Data adapted from Reference 5. ' Data adapted from Reference 3.
I 00 in
Current Status of Immunologic Pregnancy Tests Richard Derman, 1 David A. Edelman 2 and Gary S. Berger 3 3
Department of Obstetrics and Gynecology, Cornell University Medical Center, New York, New York, USA International Fertility Research Program, Research Triangle Park, North Carolina, USA University of North Carolina, Chapel Hill, North Carolina, USA
ABSTRACT Derman R, Edelman DA, Berger GS (Dept of Obstetrics and Gynecology, Cornell University Medical Center, New York, NY; International Fertility Research Program, Research Triangle Park, NC; and University of North Carolina, Chapel Hill, NC, USA). Current status of immunologic pregnancy tests. IntJ Gynaecol Obstet 17: 190-193, 1979 Information about the mechanism of various pregnancy tests is summarized. The sensitivity of these tests as well as their advantages and limitations in a clinical setting are presented and evaluated in an effort to maximize their usefulness in a clinical setting.
INTRODUCTION There are a variety of situations in which the ability to diagnose pregnancy early in gestation may be vital for both diagnoses and treatment. Although many pregnancy tests are available, there is often a lack of understanding of the mechanisms of the various tests, their sensitivity and specificity and their relative advantages and limitations. This report summarizes information about a variety of pregnancy tests in an effort to help maximize their usefulness in the clinical setting.
CATEGORIES A N D MECHANISMS T h e basis for almost all pregnancy tests is the detection of h u m a n chorionic gonadotropin (HCG) in urine or plasma. H C G is a glycoprotein produced by the placental trophoblastic cells. In the early gestational period, the H C G production in placental tissue doubles approximately every two days (6) until it reaches a peak at about the eighth week after the onset of the last normal menstrual period.
IntJ Gynaecol Obstet 17
Early pregnancy tests were qualitative in nature and were based on the biologic effects which resulted when the subject's urine was administered to an experimental animal (Table I). T h e common types of end points were luteinization of the mouse ovary, ovulation in the rabbit and sperm ejection in the frog. T h e sensitivity of these three tests was in the range of 10 IU of H C G / m l , which meant that the tests could be expected to reveal a positive result approximately 25 days after ovulation. Development of each successive test resulted in a reduction in the time required for performance and interpretation (approximately five days for the mouse test to two hours for the frog test). With the introduction of commercially available immunologic pregnancy tests in 1961, the prospect for early diagnosis of pregnancy became feasible in most clinical settings. T h e majority of immunoassays are based on the principle of indirect agglutination, either hemagglutination inhibition or latex particle inhibition, and can either be carried out in a test tube or on a slide. T h e tube tests are somewhat more sensitive (0.7-1.25 IU of H C G / m l for tube tests versus 1.0-3.5 IU of H C G / m l for slide tests), but require more time to perform (one-two hours versus two minutes). Even the slide tests (with a sensitivity of up to 3.5 IU of H C G / m l ) can, in theory, detect pregnancy within seven days of the missed menstrual period. Some of the immunologic tube and slide tests currently available are listed in T a b l e II. This table also shows the manufacturers' stated test sensitivity (ie, the minimum concentration of H C G that the test can detect) and the sensitivities based on an independent laboratory evaluation (3). In all cases, the manufacturers' stated sensitivities are lower than the actual ones. T h e manufacturers' stated sensitivities do, however, reflect the relative range of sensitivities for the different tests; the tube tests generally detect relatively lower concentrations of H C G than the slide tests.
Immunologic pregnancy tests
] 91
Table I. Historical development of pregnancy tests.
Test
Days After Ovulation Pregnancy Detectable
End Point
Testing Time
Biologic
Mouse-luteinization Rabbit-ovulation Frog sperm ejection
25 25 25
5 days 2 days 2 hr
Immunologic
Hemagglutination inhibition (tube test) Latex particle inhibition (tube test) Latex particle inhibition (slide test)
18-20
2 hr
18-20 25
1.5 hr 2 min
Radioassay
Competition with 1Z5 I-HCG for specific antibodies or receptors
6-12
1 - 2 4 hr
Table II. Sensitivities of selected immunologic pregnancy tests. 1 Pregnancy Tests Tube Tests Placentex Pregnosticon Accuspheres UCG Lyphotest
Manufacturer Roche Diagnostics 2 Organon 3 Wampole 4
Slide Tests Ortho 5 Gravindex Pregnosis Roche Diagnostics Organon Pregnosticon Dri-Dot Wampole UCG Slide 1 Data adapted from Reference 3. 2 Roche Diagnostics, Nutley, NJ, USA. 3 Organon Inc. West Orange, NJ, USA. 4 Wampole Laboratories, Cranbury, NJ, USA. 5 Ortho Diagnostics Inc, Rah tan, NJ, USA.
More sensitive than the immunologic pregnancy tests are the recently developed radioimmunoassays or radioreceptorassays which can detect plasma H C G levels of 0.5 IU of H C G / m l or less. Despite the increased sensitivity of these tests, they require specialized laboratory equipment and personnel and are not available in facilities where most pregnancy tests are performed.
ACCURACY T h e accuracy- of immunologic pregnancy tests depends upon several factors. First, the test material itself must be properly stored and the manufacturer's directions followed in performing and interpreting the test. T h e concentration of H C G in the urine or plasma is related to the duration a n d normality of the pregnancy and has a major effect on the accuracy of any test. T o determine test
Stated Sensitivity (IU of HCG/ml) 0.75-1.25 0.7-0.9 1.0 3.5 1.5-2.5 1-2 2.0
Actual Sensitivity (IU of HCG/ml) 1-2 1-3 4-6 4-14.5 2-6 3-10 4-15
accuracy, one must take into account "false-positive" readings (ie, tests read as positive when pregnancy does not exist) and "false-negative" readings (ie, tests read as negative when pregnancy does exist). T h e results from two studies that compared the percentages of correct positive test results for various immunologic slide tests performed on pregnant women at different stages of pregnancy amenorrhea are shown in Table III. For each duration of amenorrhea, there was no statistically significant difference (p > 0.10) in the percentage of correct positive test results in the two studies. In both studies, there was a statistically significant increase (p < 0.10) in the percentage of correct positive results with increasing length of amenorrhea. T h e small number of women at each duration of amenorrhea shown in Table III do not permit accurate evaluation of the correct positive (or false-negative) rates for each of the pregnancy tests. Although some studies cited in
IntJ Gynaecol Obstet 17
192
Dermtin el al
Table III. Percentage of correct test results obtained with four slide pregnancy tests performed on pregnant women in two studies. Days from Last Menstrual Period Study I1 41-51 N = 42
37-40 N = 9 %
Pregnancy Test Gravindex Pregnosis Pregnosticon Dri-Dot UCG Slide
88.9 88.9 77.8 77.8
Study II2
%
51-59 N = 24 %
40-69 N = 82
70-99 N = 42
83.3 95.2 83.3 90.5
95.8 95.8 95.8 100.0
92.7 97.6 93.9 92.7
92.9 92.9 92.9 90.5
%
%
Data adapted from Reference 5. ' Data adapted from Reference 3.
I 00 in
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