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Normalized activated protein C ratio itself not associated with increased risk of venous thromboembolism
ORIGINAL RESEARCH ARTICLE
Normalized Activated Protein C Ratio Itself Not Associated With Increased Risk of Venous Thromboembolism L.A.J. Heinemann,* A. Assmann,* M. Spannagl,† W. Schramm,† A. Dick,† C. Kluft,‡ and M.P.M. de Maat‡
Recently, discussions focused on the question whether acquired activated (APC) resistance is a clue to the observed association between venous thromboembolism (VTE) risk and oral contraceptive (OC) use, especially with the so-called third-generation OC. The objective of our study was to check the validity of acquired APC resistance regarding VTE risk in a casecontrol study. Sixty-seven women with confirmed VTE diagnosis (n 5 67) were consecutively ascertained in primary health care settings, interviewed and blood samples taken (at the earliest 6 months after VTE). Cases were age-matched to 290 population controls. Acquired APC resistance was measured as normalized APC ratio (APCRN). The effect of APC on tissue factor initiated thrombin generation was measured in plasma using a2macroglobulin attached thrombin activity as an endpoint. Higher risk (odds) ratio with 95% CI) of VTE for carriers of heterozygote Factor V Leiden mutation was confirmed [OR 5 2.72 (CI:1.51– 4.92)]. However, there is no association between VTE and the level of APCRN OR 0.65 (CI:0.35– 1.22). We conclude that acquired APC resistance, measured with a tissue factor initiated test, is unlikely to have a direct association to the clinical outcome of venous thromboembolism. CONTRACEPTION 1998;58:321–322 © 1998 Elsevier Science Inc. All rights reserved. KEY WORDS:
normalized activated protein C ratio, factor V Leiden mutation, tissue factor initiated test
*ZEG-Centre for Epidemiology and Health Research, Zepernick, and †LudwigMaximilian-Universita¨t Mu¨nchen, Klinikum Innestadt, Medizinische Klinik, Abteilung fu¨r Ha¨mostasiologie, Mu¨nchen, Germany; and ‡Gaubius Laboratory, Leiden, The Netherlands Name and address for correspondence: Lothar A.J. Heinemann, MD, DSc, ZEG-Centre for Epidemiology and Health Research, Scho¨nerlinder Straße 11-12, D-16341 Zepernick, Germany; Tel.: 149-30-9451-0120; Fax: 149-309451-0123; e-mail: [email protected] Submitted for publication September 25, 1998 Accepted for publication October 5, 1998
© 1998 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
R
ecently, a tissue factor initiated assay measuring activated protein C (APC) resistance and its increase with OC use led to speculations in the scientific community that such an “acquired APC resistance”1 could explain the reported increased risk for venous thromboembolism in users of the most recent generation of oral contraceptives found in some, but not all, epidemiological studies. We could not confirm differential association among OC types measuring APC resistance in activated partial thromboplastin time (APTT) based methods with and without factor V deficient plasma.2 Thereafter, we conducted a casecontrol study to test the clinical relevance of the tissue factor initiated assay regarding risk of venous thromboembolism (VTE). Normalized APC ratio (APCRN) was measured as the effect of APC on tissue factor initiated thrombin generation in plasma using a2-macroglobulin attached thrombin activity as an end point. Global assessment of coagulation in plasma is sensitive to disturbances in the plasma matrix due to acute inflammatory states. To minimize the influence of “acute phase proteins” blood was drawn, at the earliest, 6 months after VTE. Women were without signs of any acute or chronic disorder, inflammatory diseases or cancer. We analyzed 67 women with VTE confirmed by imaging tests and aged 15– 49 years at the time of the event. The VTE cases (southeast Germany, from 1995 to 1997) were age-matched to 290 population controls (south Germany, 1996 to 1997) without this condition (five controls/case at maximum). The mean age of cases and controls was comparable (34.2 and 34.7 years for cases and controls). Conditional regression analyses (age-matching in the 5-year age band) were performed. We confirmed the higher risk of VTE for women with the factor V Leiden (FVL) mutation (Table 1); all but one were heterozygote carriers. However, there was no association between VTE and the level of ISSN 0010-7824/98/$19.00 PII S0010-7824(98)00111-5
322
Heinemann et al.
Contraception 1998;58:321–322
Table 1. Odds ratio (95% confidence interval) for VTE and normalized APCR level by oral contraceptive use at the time of blood sampling and by factor V Leiden mutation (FVL) Cases
FVL mutation APCR: all cases and controls APCR: no FVL mutation APCR: no OC use APCR: no FVL & no OC use
Controls
Exposed
Nonexposed
Exposed
Nonexposed
OR (95% CI)
14 13 8 12 7
53 54 45 50 42
18 85 72 34 26
272 205 200 159 154
2.72 (1.51–4.92) 0.65 (0.35–1.22) 0.56 (0.26–1.22) 1.04 (0.54–2.00) 0.97 (0.43–2.20)
Exposed 5 APCRN higher; nonexposed 5 APCRN lower. The cutoff point for higher and lower APCRN values is .2.5 and #2.5, respectively.
APCRN: OR 0.65(CI:0.35–1.22) (Table 1). We found, in a stratified analysis, even a tendency toward lower relative risk estimates in women without FVL mutation, and higher without OC use at the time of the blood sampling. There was no VTE risk at all associated with APCRN in women without FVL mutation and not currently using OC. In other words, FVL mutation and OC use are mild confounders of the association between the APCRN assay for acquired APC resistance and VTE risk. No other confounders (such as cardiovascular risk factors and some hemostasiological parameters) could be identified. We conclude that the tissue factor initiated test for “acquired APC resistance” is unlikely to have a direct association to the clinical outcome “VTE”; at least, we could not identify such a link with our case-control study. Although observational studies have their merits, there are also limitations. This is the first study with limited study size; ie, the
findings need to be confirmed in other studies. The length of delay between the acute event and the “resting state,” when we took the blood samples, could be discussed. And it is unknown yet what the factors are that influence the APCRN. Furthermore, it would be very important to know if this lacking association of APCRN and VTE risk can be confirmed in a cohort approach, which unlike a casecontrol study can take into account time-dependent influences.
References 1. Rosing J, Tang G, Nicolaes GAF, et al. Oral contraceptives and venous thrombosis: different sensitivities to activated protein C in women using second- and thirdgeneration oral contraceptives. Br J Haematol 1997;97: 23–38. 2. Schramm W, Heinemann LA. Oral contraceptives and venous thromboembolism: acquired APC resistance? Br J Haematol 1997;98:491–2.
Normalized Activated Protein C Ratio Itself Not Associated With Increased Risk of Venous Thromboembolism L.A.J. Heinemann,* A. Assmann,* M. Spannagl,† W. Schramm,† A. Dick,† C. Kluft,‡ and M.P.M. de Maat‡
Recently, discussions focused on the question whether acquired activated (APC) resistance is a clue to the observed association between venous thromboembolism (VTE) risk and oral contraceptive (OC) use, especially with the so-called third-generation OC. The objective of our study was to check the validity of acquired APC resistance regarding VTE risk in a casecontrol study. Sixty-seven women with confirmed VTE diagnosis (n 5 67) were consecutively ascertained in primary health care settings, interviewed and blood samples taken (at the earliest 6 months after VTE). Cases were age-matched to 290 population controls. Acquired APC resistance was measured as normalized APC ratio (APCRN). The effect of APC on tissue factor initiated thrombin generation was measured in plasma using a2macroglobulin attached thrombin activity as an endpoint. Higher risk (odds) ratio with 95% CI) of VTE for carriers of heterozygote Factor V Leiden mutation was confirmed [OR 5 2.72 (CI:1.51– 4.92)]. However, there is no association between VTE and the level of APCRN OR 0.65 (CI:0.35– 1.22). We conclude that acquired APC resistance, measured with a tissue factor initiated test, is unlikely to have a direct association to the clinical outcome of venous thromboembolism. CONTRACEPTION 1998;58:321–322 © 1998 Elsevier Science Inc. All rights reserved. KEY WORDS:
normalized activated protein C ratio, factor V Leiden mutation, tissue factor initiated test
*ZEG-Centre for Epidemiology and Health Research, Zepernick, and †LudwigMaximilian-Universita¨t Mu¨nchen, Klinikum Innestadt, Medizinische Klinik, Abteilung fu¨r Ha¨mostasiologie, Mu¨nchen, Germany; and ‡Gaubius Laboratory, Leiden, The Netherlands Name and address for correspondence: Lothar A.J. Heinemann, MD, DSc, ZEG-Centre for Epidemiology and Health Research, Scho¨nerlinder Straße 11-12, D-16341 Zepernick, Germany; Tel.: 149-30-9451-0120; Fax: 149-309451-0123; e-mail: [email protected] Submitted for publication September 25, 1998 Accepted for publication October 5, 1998
© 1998 Elsevier Science Inc. All rights reserved. 655 Avenue of the Americas, New York, NY 10010
R
ecently, a tissue factor initiated assay measuring activated protein C (APC) resistance and its increase with OC use led to speculations in the scientific community that such an “acquired APC resistance”1 could explain the reported increased risk for venous thromboembolism in users of the most recent generation of oral contraceptives found in some, but not all, epidemiological studies. We could not confirm differential association among OC types measuring APC resistance in activated partial thromboplastin time (APTT) based methods with and without factor V deficient plasma.2 Thereafter, we conducted a casecontrol study to test the clinical relevance of the tissue factor initiated assay regarding risk of venous thromboembolism (VTE). Normalized APC ratio (APCRN) was measured as the effect of APC on tissue factor initiated thrombin generation in plasma using a2-macroglobulin attached thrombin activity as an end point. Global assessment of coagulation in plasma is sensitive to disturbances in the plasma matrix due to acute inflammatory states. To minimize the influence of “acute phase proteins” blood was drawn, at the earliest, 6 months after VTE. Women were without signs of any acute or chronic disorder, inflammatory diseases or cancer. We analyzed 67 women with VTE confirmed by imaging tests and aged 15– 49 years at the time of the event. The VTE cases (southeast Germany, from 1995 to 1997) were age-matched to 290 population controls (south Germany, 1996 to 1997) without this condition (five controls/case at maximum). The mean age of cases and controls was comparable (34.2 and 34.7 years for cases and controls). Conditional regression analyses (age-matching in the 5-year age band) were performed. We confirmed the higher risk of VTE for women with the factor V Leiden (FVL) mutation (Table 1); all but one were heterozygote carriers. However, there was no association between VTE and the level of ISSN 0010-7824/98/$19.00 PII S0010-7824(98)00111-5
322
Heinemann et al.
Contraception 1998;58:321–322
Table 1. Odds ratio (95% confidence interval) for VTE and normalized APCR level by oral contraceptive use at the time of blood sampling and by factor V Leiden mutation (FVL) Cases
FVL mutation APCR: all cases and controls APCR: no FVL mutation APCR: no OC use APCR: no FVL & no OC use
Controls
Exposed
Nonexposed
Exposed
Nonexposed
OR (95% CI)
14 13 8 12 7
53 54 45 50 42
18 85 72 34 26
272 205 200 159 154
2.72 (1.51–4.92) 0.65 (0.35–1.22) 0.56 (0.26–1.22) 1.04 (0.54–2.00) 0.97 (0.43–2.20)
Exposed 5 APCRN higher; nonexposed 5 APCRN lower. The cutoff point for higher and lower APCRN values is .2.5 and #2.5, respectively.
APCRN: OR 0.65(CI:0.35–1.22) (Table 1). We found, in a stratified analysis, even a tendency toward lower relative risk estimates in women without FVL mutation, and higher without OC use at the time of the blood sampling. There was no VTE risk at all associated with APCRN in women without FVL mutation and not currently using OC. In other words, FVL mutation and OC use are mild confounders of the association between the APCRN assay for acquired APC resistance and VTE risk. No other confounders (such as cardiovascular risk factors and some hemostasiological parameters) could be identified. We conclude that the tissue factor initiated test for “acquired APC resistance” is unlikely to have a direct association to the clinical outcome “VTE”; at least, we could not identify such a link with our case-control study. Although observational studies have their merits, there are also limitations. This is the first study with limited study size; ie, the
findings need to be confirmed in other studies. The length of delay between the acute event and the “resting state,” when we took the blood samples, could be discussed. And it is unknown yet what the factors are that influence the APCRN. Furthermore, it would be very important to know if this lacking association of APCRN and VTE risk can be confirmed in a cohort approach, which unlike a casecontrol study can take into account time-dependent influences.
References 1. Rosing J, Tang G, Nicolaes GAF, et al. Oral contraceptives and venous thrombosis: different sensitivities to activated protein C in women using second- and thirdgeneration oral contraceptives. Br J Haematol 1997;97: 23–38. 2. Schramm W, Heinemann LA. Oral contraceptives and venous thromboembolism: acquired APC resistance? Br J Haematol 1997;98:491–2.