Protein C Antigen During Pregnancy, Delivery and Puerperium

Haemostatic changes in pregnancy

Normal pregnancy is accompanied by changes in the coagulation and fibrinolytic systems. These include increases in a number of clotting factors (I, II, VII, VIII, IX and XII), a decrease in protein S levels and inhibition of fibrinolysis. As gestation progresses, there is also a significant fall in the activity of activated protein C, an important anticoagulant. While these physiological changes may be important for minimizing intrapartum blood loss, they entail an increased risk of thromboembolism during pregnancy and the post-partum period.

Laboratory issues in diagnosing abnormalities of protein C, thrombomodulin, and endothelial cell protein C receptor

OBJECTIVE

To review the current understanding of the pathophysiology of protein C deficiency and its role in congenital thrombophilia. Recommendations for diagnostic testing for protein C function and concentration, derived from the medical literature and consensus opinions of recognized experts in the field, are included, specifying whom, how, and when to test. The role of related proteins, such as thrombomodulin and endothelial protein C receptor, is also reviewed. Data Sources.-Review of the published medical literature.

DATA EXTRACTION AND SYNTHESIS

A summary of the medical literature and proposed testing recommendations were prepared and presented at the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. After discussion at the conference, consensus recommendations presented in this manuscript were accepted after a two-thirds majority vote by the participants.

CONCLUSIONS

Protein C deficiency is an uncommon genetic abnormality that may be a contributing cause of thrombophilia, often in conjunction with other genetic or acquired risk factors. When assay of protein C plasma levels is included in the laboratory evaluation of thrombophilia, a functional amidolytic protein C assay should be used for initial testing. The diagnosis of protein C deficiency should be established only after other acquired causes of protein C deficiency are excluded. A low protein C level should be confirmed with a subsequent assay on a new specimen. Antigenic protein C assays may be of benefit in subclassification of the type of protein C deficiency. The role of thrombomodulin and endothelial cell protein C receptor in thrombosis has yet to be clearly established, and diagnostic testing is not recommended at this time.

Interaction of the protein C/protein S anticoagulant system, the endothelium and pregnancy

Normal pregnancy is associated with significant changes in haemostasis, lipid metabolism and endothelial function. This suggests that maternal adaptation in these systems is required for successful pregnancy outcome. A number of acquired and heritable prothrombotic abnormalities are associated with complications in pregnancy. A common feature of these abnormalities is their ability to alter endothelial function or the protein C/protein S system and increase thrombin generation. In this review the normal function of the endothelium and the protein C/protein S system is detailed. The changes which characterize normal and complicated pregnancies are outlined and the evidence for the impact of heritable and acquired disorders of the protein C/protein S system on pre-eclampsia and fetal loss are discussed.

Congenital thrombophilia

The heritable defects which are at present accepted as proven to be associated with familial venous thrombosis are deficiency of antithrombin (AT), protein C (PC) or protein S (PS) and the FV Leiden mutation. In women from symptomatic kindred each of these defects is associated with increased risk of pregnancy-associated venous thrombosis and increased risk of fetal loss and other vascular complications of pregnancy. The risks appear to be greatest for some types of AT deficiency. These defects are very common but there is growing evidence that congenital thrombophilia is a multigene defect and abnormalities of AT or of the PC-PS system represent only part of the genetic thrombotic predisposition in symptomatic families. Currently it seems reasonable to focus resources on women with AT or PC-PS system abnormalities who are themselves already symptomatic or who come from symptomatic families rather than screen whole populations for these defects. In symptomatic families screening of females around the time of puberty allows time for education and counselling. Pregnancies should be planned, and each pregnancy in each patient managed individually. In general though, women with AT deficiency from symptomatic families require anticoagulant prophylaxis throughout pregnancy and for at least 3 months post-partum, whereas those with PC-PS system defects may require third-trimester plus post-partum prophylaxis or post-partum anticoagulant prophylaxis only.

Portal vein thrombosis concomitant with thrombophilia during pregnancy

The experience with portal vein thrombosis, an uncommon cause of portal hypertension complicating pregnancy is currently too brief to form definite conclusions regarding the management. The coexistence of the manifestations of portal hypertension as hypersplenism and esophageal varices together with Protein C and S deficiencies during pregnancy presents a real dilemma for diagnosis and management. We report the clinical follow-up of a 24-year-old woman in whom Protein C was detected in her two subsequent pregnancies besides portal vein thrombosis and discuss the changing levels of these proteins during pregnancy.

Changes in protein C and protein S levels in normal pregnancy

OBJECTIVE

The objective of the study was to determine the normal changes in the plasma concentrations of protein C and protein S that occur during each trimester of pregnancy.

STUDY DESIGN

The study was a prospective cross-sectional study of 91 normal pregnant women who had plasma concentrations of protein C and protein S measured during the first, second, and third trimesters.

RESULTS

There was no statistically significant change in antigenic or functional protein C levels during normal pregnancy. Total protein S levels also remained unchanged. Free protein S levels fell significantly from first to second trimesters (0.45 U/ml mean to 0.26 U/ml mean, p < 0.001), but no further fall occurred during the third trimester.

CONCLUSIONS

The second-trimester fall in free protein S levels is a physiologic pregnancy adaptation. Women with a thromboembolic event appearing for the first time during pregnancy should have investigations for protein S deficiency delayed until the postpartum period, to avoid misdiagnosis and treatment.

Hemostatic parameters and platelet activation by flow-cytometry in normal pregnancy: a longitudinal study

Nineteen pregnant women with uncomplicated pregnancies were studied during the first, second, and third trimesters. We measured the following hemostatic parameters: prothrombin time, activated partial thromboplastin time, fibrinogen, antithrombin III, protein C, protein S, platelet number and volume. Platelet function was examined by a cytofluorimetric method, using an anti-GPM-140 antibody which is directed against a platelet alpha granule membrane protein. Activated platelets were expressed as a percentage of the GMP-140-positive platelets over total platelets. Fibrinogen levels showed a steady increase during pregnancy; conversely prothrombin time, activated partial thromboplastin time, protein C, and antithrombin III showed no significant modifications and remained within the reference range. There was a decrease of protein S activity throughout pregnancy, although protein S antigen did not follow this trend. The decrease occurred early in pregnancy and persisted during the second and third trimesters, reaching a stable plateau. We observed no platelet volume change or activation: the percentage of activated platelets was within the normal reference range, even in late pregnancy.

Protein C, antithrombin III and plasminogen: effect of age, sex and blood group

We conducted a cross-sectional study of antithrombin III (ATIII), protein C (PC) and plasminogen (Plg) concentrations in a population of healthy plasma donors in the Trent Region. The distribution of values for protein C was log normal whereas for ATIII and Plg the distributions were positively skewed and differed significantly from normal and log normal. Males had higher antithrombin III concentrations (mean 1.10 iu/ml, range 0.72-1.65) than females (mean 1.07 iu/ml, range 0.75-1.69) (P = 0.001) and levels increased with age in women. Younger women aged 25-34 had significantly lower plasma concentrations of ATIII compared to males of similar age. For protein C, concentrations were higher in males (mean 1.07 u/ml, range 0.37-2.11) than in females (mean 1.01 u/ml, range 0.59-1.61) (P < 0.001) and levels increased with age in both sexes P < 0.001). In women, a novel difference in protein C concentration between ABO blood groups was noted. There was no significant difference in plasminogen concentration between males and females, and in women plasminogen decreased with age (r = -0.205, P < 0.001). We conclude that these variations in ATIII and protein C with age and sex are important considerations in the determination of reference ranges for these proteins.

Pregnancy and protein C deficiency

This report examines a patient with recurrent attacks of thrombo-embolism due to a protein C deficiency. Alterations in the coagulation during pregnancy and the possible consequences of an altered coagulation during pregnancy will be discussed.

[Hereditary deficiency of antithrombin III, protein C and protein S. A study of 31 patients from 8 unrelated families]

The families of eight unrelated patients were studied with regard to a hereditary deficiency in antithrombin III (ATIII), protein C, or protein S. These deficiencies were recognized in the course of investigations for deep-vein thrombosis (DVT) in the eight patients. A group of 31 individuals (patients and family members), mostly less than 40-year-old was explored. Two cases of AT III deficiency were discovered, as well as 21 of protein C deficiency, and seven of protein S. Ten of the 30 have had recurrent venous thrombosis at the time of bedrest, trauma, surgery, pregnancy, postpartum or during oral contraceptive treatment. Spontaneous DVT occurred in three cases. Seventeen patients had remained asymptomatic till then. Such patients need antithrombotic treatment during surgery or pregnancy. Prophylactic treatment with enoxaparin in one patient (deficiency in protein C) during her second pregnancy is discussed. It seems that low molecular weight heparin may be a safe alternative to unfractionated heparin. Oral anticoagulants are efficient in preventing reoccurring venous thromboembolism in patients with AT III deficiency. The questions of whether oral anticoagulants should be continued in the long-term in patients with protein C or protein S deficiency who have had a DVT, and whether asymptomatic deficient patients should be given any antithrombotic treatment outside circumstances likely to induce a DVT, remain as yet unanswered.

Clinical evaluation of protein C: a comparative review of antigenic and functional assays

Thromboembolic disease is a major complication of protein C (PC) deficiency, which is among the increasing number of recognized causes of hereditary thrombotic disease. The laboratory evaluation of PC is of the utmost importance in the accurate diagnosis of this deficiency. In this review, we describe the various types of clinical antigenic and activity assays of PC. The attributes of each type of assay are discussed, as well as the value of each assay in diagnosing the various acquired and hereditary deficiencies of PC. This basic review is intended for laboratories planning to institute PC assays.

Recurrent multiple-branch retinal arteriolar occlusions in a patient with protein C deficiency

A 34-year-old woman is presented who has recurrent, multiple, retinal arteriolar occlusions associated with a deficiency in protein C, a vitamin K-dependent anticoagulant. Protein C is a naturally occurring anticoagulant and if there is a deficiency, it can lead to episodes of thrombosis; the deficiency can be acquired or congenital. This is the first documented case of retinal arteriolar occlusion associated with a congenital deficiency of this protein. The mechanism for arteriolar occlusion in this patient is discussed, and whilst the role of protein C deficiency remains presumptive, it is strongly implicated.

Changes in coagulation and fibrinolysis during pregnancy: evidence of activation of coagulation preceding spontaneous abortion

In order to monitor physiological changes in coagulation and fibrinolysis that occur during normal pregnancy, blood samples were collected in each trimester of pregnancy from 17 volunteers. Control samples were collected from 12 non-pregnant female volunteers. As pregnancy advanced there was a rise in the basal levels of fibrinopeptide A, cross linked D-dimer fragment and the B beta 15-42 fragment and an increase in the in vitro rate of fibrinopeptide A generation. These results were consistent with an increased activation of coagulation during normal pregnancy, compensated for by a concomitant rise in fibrinolytic activity. In two patients who spontaneously aborted, evidence of uncompensated activation of coagulation could be detected before the manifestation of any clinical signs. In a second pregnancy in one of these patients similar changes were observed, but were reversed by heparin treatment and the pregnancy progressed to full-term delivery of a normal infant.

Protein S and protein C levels in Chinese women during pregnancy, delivery and the puerperium

The plasma levels of protein S and protein C related antigens were determined in a group of normal pregnant Chinese women and a group of normal non-pregnant controls, using the sandwich technique of enzyme immunoassay with commercial kits. Compared with non-pregnant controls, plasma protein S levels were significantly lower during pregnancy, labour, parturition and the early puerperium. There was no significant difference in protein S levels between pregnancy, labour and puerperium. On the other hand, maternal plasma protein C levels during pregnancy and before delivery were similar to those in controls, but a significant increase was found during the third stage of labour. This increase did not persist into the early puerperium. The observed increase in protein C level immediately after delivery in our study may represent a physiological response to counter the tendency towards venous thrombosis in the parturient women, and may help to explain the almost negligible occurrence of thromboembolism in Chinese obstetric patients.

Enhanced thrombin generation in normal and hypertensive pregnancy

We investigated the plasma levels of thrombin-antithrombin III complexes in women with uncomplicated pregnancy, patients with preeclampsia, gestational hypertension, and nonpregnant control subjects. In addition, we measured the coagulation inhibitors antithrombin III, protein C, and protein S. In normal pregnancy we observed a progressive increase in plasma thrombin-antithrombin III levels, and a decrease in protein S levels. In preeclampsia we observed increased thrombin-antithrombin III levels, reduced antithrombin III and protein C levels, and no further reduction of protein S compared with normal pregnancy. These new methods provide solid evidence for a prethrombotic state in normal pregnancy, especially in preeclampsia.

Changes in the plasma levels of vitamin K-dependent proteins C and S and of C4b-binding protein during pregnancy and oral contraception

The plasma concentrations of protein S, protein C and C4b-binding protein (C4BP) were analysed during pregnancy, in the postpartum period and in women using oral contraceptives. Free protein S, measured after precipitation of the C4BP-protein S complexes with 5% PEG 6000, was found to be 8.3 mg/l in the control group, which represents 36.3% of the total plasma protein S content (average 23.5 mg/l). The concentration of protein S was significantly decreased during pregnancy, the lowest levels occurring in the second trimester (14.8 mg/l). The values returned to normal within a few days after delivery. The concentration of free protein S was also decreased, down to an average of 3.7 mg/l at delivery, and did not return to normal within the first week postpartum. The mean concentration of protein S in women using oral contraceptives decreased to 17.7 mg/l and the free fraction went down to 6.6 mg/l. Unlike that of protein S, the plasma concentration of protein C increased during pregnancy, reaching a maximum of 135% in the second trimester. Also, it was significantly higher in the postpartum period and in women using oral contraceptives, than in controls. The level of C4BP was increased throughout pregnancy, with a maximum of 143.4% at delivery. These changes in the plasma levels of proteins C and S during pregnancy indicate that the two proteins differ in the regulation of their synthesis. The major decrease in the level of free protein S may predispose to thrombotic episodes during pregnancy, whereas the increased level of protein C may have the reverse effect. These results indicate the importance of taking into account the normal changes in the plasma levels of protein C and S during pregnancy and the use of oral contraceptives, when evaluating patients with increased risk of thromboembolic disease.

Clinical relevance of protein C

Protein C is, after activation by thrombin, a potent inhibitor of blood coagulation. An isolated deficiency of protein C increases the risk of thrombosis. The two forms of protein C deficiency, the heterozygous and the homozygous deficiency state, have different clinical features. Patients with heterozygous protein C deficiency are at a high risk to develop venous thrombosis and pulmonary embolism. In newborns with homozygous protein C deficiency with very low protein C levels (1%) a purpura fulminans like syndrome was observed. Heparin and coumarin derivatives are effective drugs in heterozygous protein C deficiency, homozygous patients may be treated either by replacement of protein C or coumarin derivatives. Decreased protein C levels were observed in various other diseases: Chronic and acute liver disease, disseminated intravascular coagulation, malignancy, postoperatively and during treatment with asparaginase. The role of protein C in these diseases to trigger thrombosis is not yet established.