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Published in final edited form as: Int J Obstet Anesth. 2021 Mar 11;46:102972. doi: 10.1016/j.ijoa.2021.102972

Associations of thrombocytopenia, transaminase elevations, and transfusion with laboratory coagulation tests in women with preeclampsia: a cross-sectional study

DJ Combs a, KJ Gray b, S Schulman c, BT Bateman d
PMCID: PMC8144064  NIHMSID: NIHMS1683136  PMID: 33798794

Abstract

Background:

Women with pre-eclampsia may develop coagulopathy, predisposing to bleeding complications. Although guidelines and prior studies conflict, we hypothesized that in preeclampsia, abnormal coagulation test results are more common in women with thrombocytopenia or transaminase elevations and increase the transfusion risk. Our objectives were to investigate: 1. patterns of coagulation testing; 2. relationships between platelet count, transaminase level, and the risk of abnormal coagulation tests; 3. risk of bleeding complications; and 4. characteristics of patients with markedly abnormal coagulation parameters. Methods: A cross-sectional study of deliveries of women with preeclampsia who had undergone activated partial thromboplastin time (aPTT) or international normalized ratio (INR) testing at one of two hospitals between 1994 and 2018.

Results:

Of 10 699 women with preeclampsia, 3359 (32.7%) had coagulation testing performed and aPTT or INR elevations were present in 124 (3.7 %). Coagulation abnormalities were more common in women with thrombocytopenia or transaminase elevations (n=82) compared with those without (n=42) (6.7%, 95% CI 5.5 to 8.2 vs 1.8%, 95% CI 1.3 to 2.5). Transfusion was more common among women with abnormal coagulation parameters (n=124) compared with those without (n=39) (33.1 vs 7.0%, P <0.001). Among 26 patients with an aPTT ≥40 s or an INR ≥1.4, six required transfusion (all had placental abruption and disseminated intravascular coagulopathy).

Conclusions:

Coagulation testing was inconsistently performed in this cohort. Platelet counts and transaminase levels inadequately detected abnormal coagulation test results. Abnormal coagulation test results were associated with a markedly higher risk for red blood cell transfusion.

Keywords: Coagulation testing, Coagulopathy, Liver function, Preeclampsia, Thrombocytopenia

Introduction

Preeclampsia occurs after 20 weeks’ gestation, affects 2–8% of pregnancies and is a leading cause of maternal and neonatal morbidity and mortality.1 Preeclampsia is heterogeneous but typically involves new-onset hypertension and proteinuria, along with other clinical and laboratory features. In particular, thrombocytopenia and coagulopathy may increase concern about obstetric hemorrhage2 and spinal-epidural hematoma with neuraxial procedures,3,4 these being preferred for all parturients, particularly those with pre-eclampsia.5–7

Although measuring platelet count is recommended in women with preeclampsia, and some uncertainty remains, the risk of spinal-epidural hematoma is thought to be very low if the count is >70 × 109/L and their function is normal.4,8 In contrast, coagulation testing in preeclampsia is not routine, and society guidelines offer inconsistent recommendations regarding such testing.1,9–13 These guidelines are also largely silent on whether or not neuraxial procedures should be performed on women with preeclampsia who have abnormal coagulation tests, although two specify that such techniques would be contraindicated.9,10 Because abnormal coagulation increases the obstetrical hemorrhage risk and some potential complications of neuraxial procedures, understanding which women with preeclampsia should undergo coagulation testing is important and should be addressed.

A study of one hundred women with preeclampsia performed more than two decades ago suggested that coagulopathy was rare, and coagulation testing unnecessary, if the platelet count was >100 × 109/L.14 Subsequent studies differed on the reliability of the 100 × 109/L platelet threshold in identifying women with abnormal test results, were often limited to particular preeclampsia subgroups, failed to adequately exclude those taking anticoagulants, and raised questions as to whether abnormal testing actually confers an increased bleeding risk.15–20 These inconsistencies likely contribute to the heterogeneity of current guidelines.

In order to better understand the use and implications of coagulation testing in women with preeclampsia, we pursued four objectives. First, we characterized the pattern of coagulation testing in patients with and without platelet and transaminase derangements. Second, we examined the association of thrombocytopenia and elevated transaminases with abnormal coagulation test results. Third, as a marker of bleeding risk, we evaluated the frequency of red blood cell transfusion in patients with abnormal coagulation test results. Fourth, we analyzed the laboratory and clinical features of the subset of cases with the most abnormal coagulation test results.

Methods

We performed a retrospective cross-sectional study of women with preeclampsia hospitalized for delivery who underwent coagulation testing, using a clinical data registry from two academic hospitals for the period between 1994 and 2018. The registry contained patient administrative, laboratory, demographic, and other data, all of which were obtained following institutional review board (Partners Human Research (2018P002043, September 11, 2018) approval. The requirement for written informed consent was waived.

Deliveries of women with preeclampsia were identified using International Classification of Diseases (ICD) codes.21,22 Delivery date was based on delivery-associated procedure codes (e.g. vaginal delivery, caesarean delivery), and patients without delivery date information were excluded. Patients using anticoagulants between the 30 days prior to the admission hospitalization and delivery were identified from the clinical registry and excluded. For all patients with abnormal coagulation studies, charts were individually reviewed to determine the delivery time and to exclude postpartum laboratory measurements. This chart review excluded two further patients using anticoagulants, as well as one patient who had liver failure secondary to acetaminophen overdose. Cases of antepartum hemorrhage or congenital coagulopathy were identified using ICD codes, and cases with abnormal coagulation testing underwent individual chart review for these diagnoses.

Red blood cell transfusion, which was used as a marker of clinically significant obstetric hemorrhage, was defined using appropriate billing codes.23 Codes for platelet transfusion, plasma transfusion, or other clotting factor transfusions were excluded. Coagulation testing was defined as a measurement of either the activated partial thromboplastin time (aPTT) or the international normalized ratio (INR). In order to minimize the capture of postpartum coagulation testing, the earliest measurement was selected for analysis, as it was for other test types studied (see below). The decision to obtain coagulation testing at both of the study institutions during the years examined was not driven by policy but rather by provider discretion. Abnormal test results were defined as values above the upper limit of normal for the test in question. For serum fibrinogen, the lower limit of normal was adjusted for late pregnancy at 3.0 g/L.24 For liver function tests (LFTs), only the aspartate transaminase (AST) or the alanine transaminase (ALT) were examined; the earliest value of the AST or ALT of all testing done between admission day and date of delivery was selected. Abnormal liver function test values were defined as those above twice the upper limit of normal, except where noted. Cases in which the aPTT was ≥40 s or the INR ≥1.4, which were thresholds selected based on guidelines and prior studies,19,25–27 underwent further chart review to collect information on estimated blood loss, blood transfusion, and anesthetic procedures.

Data were analyzed in RStudio (version 1.1.456, R version 3.6.1). Statistical significance between patient groups was calculated from contingency tables using chi-square tests or, when expected values were <5, Fisher’s exact tests. T-tests were used to assess the significance of the means of coagulation test results between patient groups. Given sample sizes for coagulation tests were in excess of 30, parametric tests were used and conformity of coagulation test results to a normal distribution was confirmed with histograms and qq plots. We conducted a sensitivity analysis using more severe derangements of aPTT and INR. For this analysis, we chose an aPTT ≥40 s because the same threshold had been used in a prior analysis;19 and for INR we chose >1.4 because an INR <1.4 is suggested for safe neuraxial placement among major guidelines.26,28 Sensitivity analyses for exclusion of antepartum hemorrhage and congenital coagulopathy, and subset analyses for patients who met platelet or transaminase criteria for hemolysis, elevated liver enzymes and low platelets (HELLP) syndrome were performed.

Results

After application of our exclusion criteria, we identified 10 699 deliveries of women with preeclampsia (Fig. 1). Platelet counts between the admission date and the delivery date were available for 10 266 (96%) patients. For our primary analysis of coagulation testing, we selected the aPTT and INR because they were the two most commonly ordered coagulation tests in our cohort. Demographic and other characteristics of deliveries, with and without aPTT or INR testing, are shown in Table 1. From the entire cohort, women with coagulation test results did not significantly differ with respect to age, race, or mode of delivery from those not having test results. In contrast to the high rates of platelet and transaminase testing within our cohort, only 3420 (32%) of cases had either an aPTT or INR performed between the admission date and the delivery date (Fig. 1). Of these, 185 (5.4%) had abnormal coagulation test results, as assessed by either an aPTT or INR above the upper limit of normal for each instance of the test in question. No meaningful temporal and institutional trends in various laboratory tests were observed (see Supplemental Figs 1 and 2). Assessment of aPTT or INR was more common in patients with thrombocytopenia or transaminase elevations (Supplementary Table 1) but was far from complete in either group. For example, only 65.9% of patients who met both platelet and transaminase criteria for HELLP syndrome received laboratory coagulation testing at any point during their admission underwent laboratory coagulation testing.

Fig. 1: Flow diagram of the procedure for defining the study population.

Fig. 1:

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Patients with coagulation tests performed only before the admission date (early) or after delivery (late) were excluded.

Table 1:

Study population characteristics

No Test for aPTT or INR
(n=7310)
n (%) or mean		 Normal aPTT or INR (n)
(n=3235)
n (%) or mean		 aPTT or INR (n) >ULNa
(n=124)
n (%) or mean (SD)		 P-valueb
Age (y)
 < 18 145 (2) 53 (2) 0 0.32
 18–34 4958 (68) 2146 (66) 88 (71)
 > 34 2207 (30) 1036 (32) 36 (29)
Race
 White 4050 (55) 1753 (54) 79 (53) 0.07
 Black 1136 (16) 581 (18) 30 (24)
 Hispanic 1033 (14) 381 (12) 9 (7)
 Unknown 318 (5) 197 (6) 11 (9)
 Asian 380 (5) 159 (5) 7 (6)
 Other 393 (5) 151 (5) 1 (1)
Cesarean delivery 3478 (48) 1975 (61) 79 (64) 0.62
Thrombocytopenia (<150 × 109/L) 815 (11) 815 (25) 57 (46) < 0.001
Antepartum hemorrhage 253 (4) 290 (9) 18 (15) 0.05
Elevated transaminasesc 1377 (19) 1184 (37) 73 (59) < 0.001
Pre-existing coagulopathy 17 (0.2) 28 (1) 2 (2) 0.3
aPTTd (s) NA 27.5 (2.9) 40.7 (16.9) < 0.001
INRd NA 1.0 (0.1) 1.3 (0.4) < 0.001
Fibrinogend (g/L) NA 4.99 (1.18) 3.89 (1.92) < 0.001
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a.

ULN: upper limit of normal

b.

Fisher’s exact, chi-square, and two sample t-tests used where appropriate to compare values in the third and fourth column.

c.

Includes only aspartate transaminase (AST) or the alanine transaminase (ALT)

d.

Not all patients received all three coagulation tests (see Table, Supplemental Digital Content 1). Means calculated for the subset of patients who received the test in question.

aPTT: activated partial thromboplastin time. INR: international normalized ratio

Only 124 of 3359 (3.7%) cases had abnormal coagulation test results between admission and delivery. An elevated aPTT or INR was more common among women with a platelet count <150 × 109/L or with an ALT or AST higher than twice the reference range (6.7%, 95% CI 5.5 to 8.2), compared with women without thrombocytopenia or transaminase elevations (incidence 1.8%, 95% CI 1.3 to 2.5%, P <0.001, see also Supplemental Table 2). However, most tested patients with thrombocytopenia (93.5% of those with platelet count <150 × 109/L and 91.2% with platelet count <100 × 109/L) or transaminase elevations (91.9% of patients with an AST or ALT above twice the upper limit of normal) had normal coagulation test results. These associations persisted when analyzed for individual coagulation test types, when only cases with diagnostic codes for preeclampsia with severe features were included, when diagnostic codes for antepartum hemorrhage or congenital coagulopathy were excluded, or when the analysis was limited to cases with more severe coagulation test result abnormalities (Supplemental Table 3).

With respect to hemorrhage, although hemoglobin concentrations on hospital admission were similar (mean and standard error of 124 ± 17 g/L vs 121 ± 14 g/L), packed red blood cell transfusion occurred in 124 (31.5%) of those with abnormal coagulation test results compared with 29 (7.0%) women who had normal tests. Rates of packed red blood cell transfusion were higher in patients with coagulation test result abnormalities than in those with thrombocytopenia or transaminase elevations but normal results (Supplemental Table 4).

To better understand the basis for the high transfusion rates (and, by inference, increased bleeding risk) in patients with abnormal coagulation test results, we examined the cases with the most elevated test values. If an abnormally elevated coagulation test confers an increased risk of bleeding complications in women with preeclampsia, we hypothesized that such complications would most likely have occurred in patients with the most aberrant values, so an analysis of those cases might reveal possible common features. Informed by a combination of guideline recommendations and prior studies,19,25–27 we selected patients with an aPTT ≥40 s or INR ≥1.4 for inclusion in our subset of cases with markedly elevated coagulation testing. Of 110 patients meeting these criteria, complete records were available for the 65 cases from 2006 onwards. These 65 cases were reviewed to impose our exclusion criteria (n=30) and eliminate spurious aPTT or INR elevations (determined by associated documentation and repeat testing, n=9). Fig. 2 shows laboratory test data from the remaining 26 cases, grouped by the presumed etiology of coagulopathy, with nine cases qualified by both INR and aPTT criteria, 11 by aPTT only, and six by INR only. Among the presumed etiologies of coagulopathy, there was no clear pattern with respect to aPTT or INR elevations. Antepartum fibrinogen levels were available for 24 cases, and 14 women had a fibrinogen level <3.0 g/L, which is the lower limit of normal during the third trimester of pregnancy.24 The six lowest fibrinogen results (range 0.69–1.54 g/L) were all from cases having an abruption. Only 12 of the 24 cases had thrombocytopenia (<150 × 109/L), 18 had an elevated ALT or AST above the upper limit of normal, and four cases had neither thrombocytopenia nor an ALT or AST above the upper limit of normal.

Fig. 2: Laboratory tests results in the 26 cases with the most extreme aPTT or INR values.

Fig. 2:

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The lowest (platelet, fibrinogen) or highest (aPTT, INR, AST, ALT) value between admission and delivery is plotted and symbols denote the presumed etiology coagulopathy: abruption (circle), acute fatty liver of pregnancy (AFLP) (triangle), hemolysis, elevated liver enzymes and low platelets (HELLP) (square), and other (+)

Table 2 shows the management and bleeding complications of the 26 cases grouped by presumed coagulation etiology. Hemorrhage was far more common, and more severe, among cases of abruption. All seven cases with abruption had significant hemorrhage and required blood product transfusion. Of the other cases, only two had an estimated blood loss ≥1000 mL (1000 mL and 1200 mL), and neither patient received a blood product transfusion. Three cases without abruption did receive blood product transfusion, but per chart review, these products were fresh frozen plasma, cryoprecipitate, and/or platelets given to correct laboratory abnormalities in the absence of hemorrhage.

Table 2:

Management and hemorrhage information in the 26 cases with the most extreme aPTT or INR values

Type Cases (n) Cesarean delivery (n) EBL, range (mL) Transfused (n)a Units transfused, range (n)
HELLP 8 7 500–1200 1 0–3
AFLP 4 3 600–850 2 0–4
Abruption 7 3 1000–4000 7 6–27
Other 7 4 500–1000 0 0
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HELLP: hemolysis, elevated liver enzymes and low platelet count. AFLP: acute fatty liver of pregnancy. EBL: estimated blood loss.

a.

Transfusions for cases of HELLP and AFLP did not include packed blood cells.

Discussion

Coagulation testing was performed inconsistently in patients with preeclampsia. Abnormal coagulation test results were more commonly performed in patients with thrombocytopenia or elevated transaminases, but the majority of women who were tested had normal coagulation parameters, even those with concurrent platelet or liver function test abnormalities, and most abnormal test results were minor (aPTT <40 s or INR <1.4). Abnormal coagulation test results were associated with a more than four-fold increased risk of red blood cell transfusion. Among 26 cases with the most severe test derangements, only the seven women experiencing an abruption and disseminated intravascular coagulopathy (DIC) had significant hemorrhage.

This study is the largest analysis of coagulation testing in preeclampsia. Unlike many prior studies, we included all types of preeclampsia and only excluded cases in which an anticoagulant was used. By focusing our analyses on a smaller subset with the most extreme coagulation test results, we were able to identify and exclude cases with irrelevant or erroneous laboratory testing while gathering key information pertaining to case management and hemorrhagic complications.

Leduc et al. reviewed 100 cases of severe preeclampsia and concluded that coagulation testing could be omitted for patients with platelet counts >100 × 109/L.14 Subsequent studies examining coagulation testing and this platelet threshold reported inconsistent results, some supporting a higher threshold and others failing to find any association between platelet count and coagulation testing.15–20 These studies included different combinations of hypertensive disorders and coagulation tests, and anticoagulant use was addressed inconsistently, if at all. Only one small study reported an association between abnormal liver function testing and abnormal coagulation testing.17

Our findings suggest that platelet count or transaminase levels may have little value in identifying patients on whom to perform coagulation testing, despite the observed associations. In this study, cases with more than trivial abnormalities in coagulation testing were rare, and even those with thrombocytopenia or transaminase elevations were unlikely to have abnormal coagulation testing. Here, it is likely that clinically-driven testing selected those with more severe disease, giving an overestimate of the strength of association between platelet count, transaminases, and coagulation tests. Finally, even among the subset of cases with the most extreme test results, some cases had no thrombocytopenia or transaminase elevations, raising concern for false negatives if using a platelet count or LFT-driven testing scheme. Thus, it would seem that platelet count or transaminase level cut-offs offer weak discriminative power for guiding coagulation testing.

The higher transfusion rates in patients with coagulation test abnormalities suggest that such patients require heightened vigilance for hemorrhage, but given that testing was clinically-driven and sporadic, these results should be interpreted cautiously. In the 26 cases with the most extreme coagulation test abnormalities, significant hemorrhage was confined to the seven women with an abruption and very low fibrinogen levels, raising the question of whether abnormal coagulation test results in preeclampsia confer an increased bleeding risk in the absence of DIC. It is emphasized that the question is not whether etiologies other than abruption (such as HELLP, acute fatty liver of pregnancy or, preeclampsia with severe features) increase the risk of DIC or hemorrhagic complications, but rather whether certain abnormal test values in patients with preeclampsia or related disorders signify a clinical bleeding risk. If they do not, then expanded coagulation testing or blood product transfusions for abnormal test results may have little clinical value in patients with preeclampsia without DIC or active bleeding.

Coagulopathy and thrombocytopenia are closely tied to liver dysfunction, all of these having a relationship with preeclampsia severity, and DIC, and consumption of platelets and coagulation factors. The mechanisms underlying the association between thrombocytopenia, coagulopathy, and transaminitis in preeclampsia are complex, but include hepatic platelet clearance coupled to thrombopoietin production29 and hepatic synthesis of clotting factors and endogenous inhibitors of coagulation. In addition, abnormal placentation30 and imbalanced angiogenic signaling31 can trigger consumptive coagulopathy DIC, in part through exposure of otherwise latent maternal and placental sources of tissue factor.32,33 Future studies are needed to better understand hematologic dysfunction in preeclampsia.

Our study is subject to the limitations inherent in its design. Our population comprised patients admitted to one of two academic hospitals in the same city, however physiological studies should be generalizable to other populations. Coagulation testing was not performed on all women with preeclampsia during the study period, and selection of cases that received coagulation testing likely biases the sample toward those with more severe disease. Only a prospective study is likely to provide higher testing rates; yet, because markedly abnormal test results are rare, assessment of clinical outcomes (e.g. hemorrhage, transfusion rates) in a prospective manner would likely require very large numbers of patients. All potential elements of a given preeclampsia diagnosis (e.g. the degree of hypertension) were not included in our dataset, and this limited our ability to assess additional clinical features of preeclampsia that might be associated with abnormal coagulation studies. Some data elements were collected using billing codes, which may imperfectly capture clinical information. The data are collected across a long period of time during which clinical practice may have changed. The coagulation tests studied here were the ones most commonly ordered in this cohort, but we cannot comment on whether these tests are necessarily best for the evaluation of bleeding risk in parturients, with or without preeclampsia. Furthermore, our study cannot directly assess the clinical benefit of coagulation testing.

In conclusion, markedly abnormal coagulation test results in preeclampsia are rare, and our findings raise questions about their clinical significance if such results are not accompanied by DIC or hemorrhage. To answer these questions, future clinical studies might focus on larger numbers of patients with HELLP, acute fatty liver of pregnancy, and abruption, which were diagnoses found here in the majority of cases with the most abnormal coagulation test results. Future studies of preeclampsia biology may offer another way forward to better understand hematologic dysfunction in preeclampsia and guide prospective clinical studies.

Supplementary Material

1

Highlights.

  • Laboratory coagulation testing of women with preeclampsia occurs inconsistently

  • Abnormal coagulation markers are associated with low platelets and high liver tests

  • This association is a limited guide for decision-making on coagulation testing

  • Transfusion was four-times more common if coagulation markers were abnormal

  • Severe coagulation derangements paired with bleeding only in those with abruption

Funding

Kathryn J. Gray was supported by NIH NHLBI K08 (HL146963) career development award. Sol Schulman was supported by an NIH Director’s Early Independence (1DP5OD028129) award. Support was provided from institutional and/or departmental sources.

Declaration of interests

Brian T. Bateman reports receiving grants to his institution from Eli Lilly, GlaxoSmithKline, Pacira BioSciences, Baxalta, Pfizer for unrelated topics and having served on an expert panel for a postpartum hemorrhage quality improvement project conducted by the Association of Women’s Health, Obstetric, and Neonatal Nurses and funded by a grant from Merck for Mothers. He serves as a consultant to Aetion and the Alosa Foundation for unrelated projects. Kathryn J. Gray reports having served as a consult for BillionToOne and Quest Diagnostics on genetic carrier screening and Illumina, Inc. on adverse pregnancy outcomes. Sol Schulman reports serving as a consultant for and receiving grants to his institution from CSL Behring for unrelated research activities. David J. Combs reports no conflicts of interest.

Footnotes

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Supplementary Materials

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NIHMS1683136-supplement-1.docx (7.4MB, docx)

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