key: cord-0980183-abgce27s
authors: Al‐Samkari, Hanny; Song, Fei; Van Cott, Elizabeth; Kuter, David J.; Rosovsky, Rachel
title: Evaluation of the Prothrombin Fragment 1.2 in Patients with COVID‐19
date: 2020-08-11
journal: Am J Hematol
DOI: 10.1002/ajh.25962
sha: ea7b1ef87a0fe8aeaddca03d4bec562eb46fcfc0
doc_id: 980183
cord_uid: abgce27s

INTRODUCTION: Coronavirus disease 2019 (COVID‐19) may cause a hypercoagulable state. The D‐dimer is frequently elevated in COVID‐19, but other markers of coagulation activation, including the prothrombin fragment 1.2 (PF1.2) are poorly described. METHODS: We studied hospitalized adults with COVID‐19 and PF1.2 measurement performed at any time during hospitalization. We evaluated the relationship between PF1.2 and synchronously measured D‐dimer. We utilized receiver operating characteristic (ROC) analysis to evaluate optimal thresholds for diagnosing thrombosis and multivariable logistic regression to evaluate association with thrombosis. RESULTS: 115 patients were included [110 (95.7%) critically ill]. PF1.2 and D‐dimer were moderately positively correlated (r=0.542, P<0.001) but significant discordance was observed in elevation of each marker above the laboratory reference range (59.0% elevated PF1.2 vs. 98.5% elevated D‐dimer). Median PF1.2 levels were higher in patients with thrombosis than those without (611 vs. 374 pmol/L, P=0.006). In ROC analysis, PF1.2 had superior specificity and conferred a higher positive likelihood ratio in identifying patients with thrombosis than D‐dimer (PF1.2 threshold of >523 pmol/L: 69.2% sensitivity, 67.7% specificity; >924 pmol/L: 37.9% sensitivity, 87.8% specificity). In multivariable analysis, a PF1.2 >500 pmol/L was significantly associated with VTE [adjusted odds ratio (OR) 4.26, 95% CI, 1.12‐16.21, P=0.034] and any thrombotic manifestation (adjusted OR 3.85, 95% CI, 1.39‐10.65, P=0.010); conversely, synchronously measured D‐dimer was not significantly associated with thrombosis. 90.6% of patients with a non‐elevated PF1.2 result did not develop VTE. CONCLUSIONS: PF1.2 may be a useful assay, and potentially more discriminant than D‐dimer, in identifying thrombotic manifestations in hospitalized patients with COVID‐19. This article is protected by copyright. All rights reserved.

Coronavirus disease 2019 is associated with a hypercoagulable state, and coagulation-related complications have been associated with considerable morbidity and mortality in critically ill patients with COVID-19. 1, 2 Numerous studies have reported elevated rates of venous thromboembolism (VTE) 2-6 and other thrombotic complications 1,2 in critically ill patients with COVID-19 as well as an association of elevated plasma D-dimer concentrations with critical illness and mortality 1, 7, 8 . Autopsy studies have reported fibrin thrombi within distended small vessels and capillaries 9 as well as a high rate of occult pulmonary vessel thrombosis 10 .

The etiology of the near-universal D-dimer elevation in critically ill patients with COVID-19 remains unclear. Given the elevated rates of thrombotic complications observed in these patients, the assumption can be made that elevated D-dimer levels are secondary to increased and pathologic thrombin generation and fibrin clot formation. However, many patients with COVID-19 have dramatic D-dimer elevations in the absence of clinical or radiographic evidence of thrombosis or laboratory evidence of disseminated intravascular coagulation (DIC). The contribution of other potential causes of D-dimer elevation, such as hyperfibrinolysis 11 , direct lung injury 12 , or reduced D-dimer clearance 13 in patients with COVID-19 is not known.

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Little is known about other serological markers of coagulation activation in COVID-19. One such marker, the prothrombin fragment 1.2 (PF1.2), is released from prothrombin by the catalytic action of the prothrombinase complex 14 . It is a well-described marker of coagulation activation that is elevated in individuals with acute thrombosis 15 near universal and frequently dramatic D-dimer elevations being observed. Therefore, the goal of this study was to evaluate the PF1.2 in patients with COVID-19, describing rates of elevation, relation to synchronously measured D-dimer, and association with thrombosis.

This study was approved by the Institutional Review Board of Partners Healthcare (approval PHS/2020P000994). All patients with a prothrombin fragment F1.2 assay drawn at the Massachusetts General Hospital from April 1, 2020 through May 6, 2020 (inclusive of the peak of the pandemic in Massachusetts) were identified using the hospital laboratory information system. 

Plasma D-dimer levels were measured using the VIDAS enzyme-linked immunosorbent assay (bioMérieux), with a reference range of <500 ng/mL FEU. This article is protected by copyright. All rights reserved.

Plasma PF1.2 levels were measured using an enzyme immunoassay (Quest Diagnostics) with a reference range of 41-372 pmol/L.

All analyses comparing PF1.2 and D-dimer measurements compared PF1.2 and D-dimer measurements obtained on the same day for each patient (synchronous measurements). The relationship between PF1.2 and D-dimer levels for the study population was evaluated graphically and via calculation of Spearman correlation coefficients. Median PF1.2 and D-dimer levels in those patients with and without VTE or thrombotic complications were compared using the Mann-Whitney U test. Receiver operating characteristic (ROC) analysis was performed and PF1.2 and D-dimer thresholds for optimal discrimination between those who developed thrombotic complications and those who did not develop thrombotic complications were obtained via calculation of Youden's J statistic 19 .

Additionally, the specificity of each test in identifying patients with thrombotic manifestations was further evaluated by specifying an optimal specificity threshold of the ROC curve, defined as the highest specificity that maintained a sensitivity of at least 30%. Multivariable logistic regression controlling for age, sex, and body mass index (BMI) was performed to assess the association of PF1.2 and D-dimer with VTE and any thrombotic manifestation, as well as the This article is protected by copyright. All rights reserved. association of PF1.2 with mortality. Thresholds for PF1.2 and D-dimer used in multivariable regression were derived from thresholds specified by the Youden's J statistic in ROC analyses. Given the known suppression of these markers by anticoagulation 20, 21 and to avoid confounding on this basis, patients receiving therapeutic anticoagulation at the time of the assay measurement were excluded from all of the above analyses. For patients with multiple PF1.2 assays performed, the first value was used for the above analyses.

In patients with multiple PF1.2 assays drawn longitudinally over time who had a radiographically-confirmed VTE within 4 days of one of the PF1.2 assays, the trend of the PF1.2 and D-dimer in relation to the VTE and initiation of therapeutic anticoagulation was examined graphically.

Statistical analysis was performed and graphs for figures were prepared using GraphPad Prism 7 (GraphPad, Inc., San Diego, CA), and Microsoft Excel 360 (Microsoft Corp., Seattle, WA). Missing data was not imputed. Any results above the upper limit of the assay were entered as 1 unit higher than the assay upper limit value for all analyses using continuous variables.

This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

In ROC analysis, the optimal threshold for a randomly-drawn PF1.2 to identify patients who developed either VTE alone or any thrombotic manifestation during hospitalization was >523 pmol/L (69.2% sensitivity and 67.7% specificity for VTE alone, 62.1% sensitivity and 75.5% specificity for any thrombotic manifestation, Figure 3 ). The optimal specificity thresholds of the PF1.2 to identify patients who developed VTE or any thrombotic manifestation were >1156 pmol/L (38.5% sensitivity and 90.8% specificity) and >924 pmol/L (37.9% sensitivity and 87.8% specificity), respectively, hospital course. Our findings that the PF1.2 may be more discriminant than synchronously measured D-dimer at identifying patients with COVID-19 who experience thrombosis requires confirmation in a study in which PF1.2 assays are drawn at a common point along the course of illness, such as initial presentation or ICU admission. Additionally, it bears mention that the PF1.2 assay is not currently typically performed in-house by most hospitals, although it is readily available as a send-out test in major reference laboratories (such as LabCorp or Quest Diagnostics in the United States).

In conclusion, we observed that the PF1.2 was elevated in most critically ill patients with COVID-19, but to a lesser extent than the D-dimer. D-dimer was almost universally elevated, and frequently to much a greater degree than PF1.2.

The PF1.2 was more specific than synchronously measured D-dimer in identifying patients who experienced thrombosis and was significantly associated 

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