Coagulopathy in children with covid-19: features of the acute period of the disease and long-term consequences

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Introduction

COVID-19 is associated with changes in the blood coagulation system. Patients with COVID-19 usually develop thrombotic complications [1]. Hemorrhagic, cytopenic, or thrombohemorrhagic syndromes can be clinical signs of hemostasis abnormalities [2]. COVID-19 is characterized by microangiopathy represented by destructive thrombovasculitis and microthrombosis of the pulmonary artery capillaries [3]. Although these data remain inconsistent, damage to microvessels by the virus was suggested to be an important element of COVID-19 pathogenesis [4; 5]. In patients with COVID-19, congestion of the capillaries in the interalveolar septa and branches of the pulmonary artery with sludge of erythrocytes was seen with perivascular and intravascular hemorrhages [6]. The exact pathophysiological mechanisms underlying hemostasis changes remain unclear [7; 8].

On the one hand, endothelial cell dysfunction caused by COVID-19 can lead to thrombin overproduction and suppressed fibrinolysis, indicating hypercoagulation in patients with COVID-19 [9]. On the other hand, neutrophilic leukocytes, which form the first line of immune defense, are stimulated in patients with viral infections. The cells migrate to the inflammation site, produce reactive oxygen species, interleukins, and chemokines, and form neutrophil extracellular traps (NETs) [10]. Besides antimicrobial (phagocytic) function, NETs play a fundamental role in procoagulant effects, which involve platelets, von Willebrand factor, tissue factor, extracellular histones, neutrophil cell serine proteases, and fibrinogen [11]. The platelet-neutrophil aggregates enhance the formation of NETs, leading to major disturbances in coagulation balance towards hypercoagulation [12].

Often, changes in the blood coagulation system in patients with COVID-19 are hidden and unrecognized but play an important role in its pathogenesis and clinical signs [2].

Patients with COVID-19 were shown to have increased fibrin clot formation in their blood. Increased levels of acute-phase proteins during COVID-19 infection lead to increased levels of fibrinogen (i.e. one of the acute-phase proteins). At the same time, the aggregation ability of platelets increases, causing the initiation, subsequent intensification, and spread of the coagulation process [12]. According to some authors, the onset of the disease is usually associated with hypercoagulation without signs of consumption coagulopathy or disseminated intravascular coagulation (DIC) syndrome. Levels of D-dimer significantly increase, and prothrombin time (PT) with fibrinogen levels slightly increase [2].

The onset of the disease may be associated with slight thrombocytosis. Several data suggested that thrombocytopathies, both thrombocytopenia and platelet hyperactivation, are typical for COVID-19, leading to hypercoagulation and immune response dysfunction. Besides it is believed that SARS-CoV-2 directly affects platelets, leading to enhanced apoptosis [13]. Patients with COVID-19 can develop hypercoagulation but not consumption coagulopathy, as in DIC or sepsis-induced coagulation [14].

In most cases, literature described changes in the coagulation system during COVID-19 in adult patients [3; 4; 15; 16]. However, we should remember that most routine coagulation parameters are highly dependent on age (especially during the first year of life). Therefore, coagulation profile changes in adults may not always coincide with changes in hemostasis in children. However, there are currently some data on how SARS-CoV-2 affects the blood coagulation system in children.

Thrombotic microangiopathy (TMA) in children is known to be one of the key elements in the pathogenesis of multisystem inflammatory syndrome (MSI) associated with COVID-19 [7]. Diorio et al. showed that 38 % of pediatric patients with COVID-19 (even if they had minimal clinical symptoms or even asymptomatic disease) had signs suggesting the activation of the complement, a biomarker associated with blood vessel damage, which corresponds to the clinical diagnostic criteria for thrombotic microvascular complications (i.e. the main cause of severe COVID-19 in adults) [17]. According to other authors, SARS-CoV-2 is a respiratory infection that causes activation of the hemostasis system, manifesting as immunothrombosis or thromboinflammation. In their turn, these processes can lead to the development of alveolar vasculitis and trigger the development of pneumonia [8]. High levels of D-dimer in patients aged 0 to 18 years may suggest a risk of developing thrombotic complications [5]. Several publications showed that children with COVID-19 had increased platelet activation, which, in turn, contributed to the formation of platelet-leukocyte aggregates. These data suggest that COVID-19 infection can be associated with platelet dysfunction [18].

Thus, data on hemostasis in children during the acute period of COVID-19 are scarce. Adequate data on COVID-19 sequelae are missing. Studying changes in coagulation parameters in children during different periods of COVID-19 can help predict the development of complications in their blood coagulation system and, therefore, take the necessary preventive and therapeutic measures.

Study aim. This study aimed to assess patterns in coagulation system changes in children in the acute period of COVID-19 and at follow-up.

Materials and Methods

Within a retrospective cohort study, we examined children aged 1 to 18 years old with confirmed COVID-19 from 2020 to 2022 in Yekaterinburg. Three age groups were identified, 1–5, 6–10, and 11–18 years, as per the recommendations of the International Society on Thrombosis and Hemostasis [19]. The patients were examined during the acute period of COVID-19 infection (examination 1, 5.4 ± 0.61 days) and at follow-up after disease resolution (examination 2, 131.8 ± 10.05 days). Results were compared with the coagulation profiles of healthy children of the same age who were included in the control group (Table 1).

 

Table 1

Number of children with COVID-19 examined

Age, years	Examination 1	Examination 2	Control group
1–5	25	15	42
6–10	29	17	34
11–18	76	20	37
Total	130	52	113

 

The test parameters included those to assess the vascular-platelet (platelet count, platelet aggregation) and plasma-coagulation (INR, aPTT, thrombin time, fibrinogen, antithrombin-III, SFMC, euglobulin lysis, D-dimer) components of hemostasis.

Platelet count was assessed using an XS-1000i hematology analyzer. Platelet functional activity was studied using a Chronolog-570 optical aggregometer; adenosine diphosphoric acid (ADF Chronopar) was used as an aggregation inducer. Fibrinogen and other coagulation parameters were determined using a Sysmex-5100c automatic coagulation analyzer with proprietary closed analytical systems.

Fibrinolytic activity of plasma was assessed by euglobulin clot lysis time.

Data were statistically processed using Statistica for Windows application package. The significance of differences in mean values and frequency of detection of signs in different groups was assessed using parametric tests with Student’s t-test. Differences were considered significant if p < 0.05.

Children’s parents or guardians signed a voluntary written consent for the examination. The inclusion criteria included patients’ age and confirmed COVID-19 diagnosis (U 07.1).

Results and Discussion

In children of the test group (n = 130), severity of COVID-19 was moderate (n = 110; 84.0%), severe (9 patients; 6.9%), or mild (11 patients; 8.5 %) (Table 2).

 

Table 2

Severity of COVID-19 in children of different age groups, n = 130

Age, years	Severity
	Mild, n/%	Moderate, n/%	Severe, n/%
1–5	1 / 4	21 / 84	3 / 12
6–10	2 / 6.9	21 / 72	6 / 20.7
11–18	8 / 10.5	68 / 89.5	–
Total	11 / 8.5	110  / 84.6	9 / 6.9

 

At the onset of the disease, regardless of its severity, children had the following parameters decreased: platelet aggregation (1–5 years: p = 0.02; 6–10 years: p < 0.01; 11–18 years: p < 0.001) and thrombin time (p < 0.001 for all age groups). COVID-19 is associated with increased levels of acute-phase proteins, such as fibrinogen [12], which can lead to shortened thrombin time in children (p < 0.001). Expectedly, high levels of fibrinogen and decreased time of clot formation in the plasma were associated with increased levels of soluble fibrin-monomer complexes (SFMC) (p < 0.001). Besides, an increase in the level of fibrin degradation products, D-dimer (p < 0.001), was detected. In addition, euglobulin lysis time significantly increased (p < 0.001), suggesting inhibition of fibrinolysis and the development of a prethrombotic state due to hypercoagulation.

For children of the younger age group (1–5 years), hypercoagulation predisposing factors were detected, including thrombocytosis (p = 0.02), decreased INR (p < 0.001), and decreased aPTT (p < 0.001) (Table 3).

 

Table 3

Coagulation profile of children in the acute period of COVID-19, M ± m

Parameter	Age, years
	1–5			6–10			11–18
	Test group, n = 25	Control group, n = 42	p	Test group, n = 29	Control group, n = 34	p	Test group, n = 76	Control group, n = 37	p
Platelets, 109/L	369.60 ± 19.88	323.5 ± 9.95	0.02	298.20 ± 15.96	307.1 ± 6.57		265.00 ± 13.85	270.3 ± 9.18
Platelet aggr., %	60.60 ± 2.09	65.8 ± 1.13	0.02	59.60 ± 2.25	66.5 ± 1.46	0.01	56.20 ± 1.58	64.9 ± 1.04	< 0.001
INR	0.90 ± 0.02	1 ± 0.01	< 0.001	1.00 ± 0.01	1 ± 0.008		1.00 ± 0.01	1.00 ± 0.01
aPTT, s	32.00 ± 0.95	35.8 ± 0.54	< 0.001	33.70 ± 1.38	34.9 ± 0.53		33.10 ± 0.67	34.1 ± 0.56
Platelet time, s	16.50 ± 0.18	18.2 ± 0.17	< 0.001	17.30 ± 0.20	18.2 ± 0.162	< 0.001	16.80 ± 0.12	18.3 ± 0.12	< 0.001
Fibrinogen, g/L	3.10 ± 0.15	2.5 ± 0.07	< 0.001	2.80 ± 0.14	2.40 ± 0.055	< 0.001	3.40 ± 0.10	2.5 ± 0.06	< 0.001
AT – III %	108.80 ± 5.45	109.5 ± 1.41		107.50 ± 3.16	106.60 ± 1.18		105.00 ± 1.92	105.3 ± 1.24
SFMC, nmol/L	5.90 ± 0.37	4.7 ± 0.16	< 0.001	5.80 ± 0.34	4.50 ± 0.176	< 0.001	6.70 ± 0.24	5.2 ± 0.13	< 0.001
Euglobulin lysis, min	28.10 ± 3.87	9.5 ± 0.5	< 0.001	17.60 ± 2.63	7.30 ± 0.244	< 0.001	18.90 ± 1.39	7.00 ± 0.24	< 0.001
D-dimer, μg/L	1684.10 ± 585.6	188.7 ± 22.7	< 0.001	7473.14 ± 3392.7	172.2 ± 18.64	< 0.001	2868.70 ± 1401.88	211.58 ± 29.43	< 0.001

 

The above-mentioned parameters (aPTT, fibrinogen, SFMC, platelet aggregation, and D-dimer) serve as diagnostic criteria for hypercoagulation syndrome [2]. An analysis was performed to determine the frequency of the changes in hemostasis parameters (Figure 1, a–c).

 

Fig. 1. Proportion of patients with changes in coagulation parameters in the acute period of COVID-19, %: a – children aged 1–5 years; b – 6–10 years; c – 11–18 years

 

Euglobulin lysis time differed from normal limits to the highest extent, i.e. it was significantly increased in the majority of children (in 80 % of children 1–5 years old, 62.1 % of children 6–10 years old, and 65.8% of children 11–18 years old). According to Galstyan, increased D-dimer levels were observed only in 43% of patients with mild disease and in 60 % with severe COVID-19 [20]. In a given study, the proportion of children with increased blood levels of D-dimer was 19.7 %, 28.0 %, and 31.0 % in 11–18, 1–5, and 6–10–year old children, respectively. Patients with high D-dimer levels are at risk of venous thromboembolic complications [2].

The proportion of patients with platelet aggregation below normal limits was almost similar in different age groups (40 %, 37.9 %, and 51.3%, respectively, in patients 1–5, 6–10, and 11–18 years old). A similar situation was seen with aPTT, with the values below normal seen in 28.9–44.0 % of patients. High levels of SFMC were more often seen in children over 11 years of age (53.9 % vs. 28.0 % and 27.6 % of 1–5 and 6–10–year old children), p < 0.01. Significantly increased levels of fibrinogen were also seen in the test group (p < 0.01). Of note, there were children aged 11–18 years with both thrombocytopenia (15.8 %) and thrombocytosis (17.11 %).

Thus, the acute period of COVID-19 in children was associated with significant changes in the blood coagulation parameters, even though most of our patients had mild or moderate COVID-19 (i.e. 93 %). The abnormalities concerned the vascular-platelet and coagulation components of hemostasis, as well as the fibrinolytic system.

According to several authors, patients with COVID-19 have increased platelet aggregation [2; 12]. In contrast, all children in this study had this parameter decreased. SARS-CoV-2 may have a direct effect on platelets, changing the properties of blood cells [21].

Changes in the parameters of the coagulation component of hemostasis (decreased thrombin time, increased fibrinogen, decreased aPTT) suggested the activation of the intrinsic coagulation pathway and disruption of the final stage of the coagulation process (i.e. conversion of fibrinogen into fibrin under the influence of thrombin).

Pronounced abnormalities were detected in the fibrinolysis system. High levels of fibrinogen (most likely due to inflammation) led to the accumulation of soluble fibrin-monomer complexes (SFMC), which are intermediate products between fibrinogen and fibrin, and also lead to increased euglobulin lysis time in plasma. These changes suggested inhibition of fibrinolysis processes. The activation of coagulation during COVID-19 in children was confirmed by high levels of fibrin degradation products, which were assessed based on D-dimer test.

These changes can be predictors for the development of thrombotic complications in children, whereas microvascular thrombosis can underlie damage to many organs, up to multiple organ failure [22]. Therefore, it is important to study how long changes in the hemostasis system can persist in children and whether they are still at risk of thrombotic disorders.

Authors from Belarus [22] showed that levels of D-dimer and SFMC in the blood remained high in children with COVID-19 even after 90 and 180 days from the onset of the disease. High levels of fibrin may be the result of a prolonged inflammation. In this case, D-dimer is a marker of the inflammatory response to damage to the vascular wall rather than a marker of clot formation.

We reviewed coagulation profiles of children who underwent COVID-19 (n = 52). The studies were done 131.8 ± 10.05 days from the onset of the disease. At the onset of the disease, the most pronounced changes were detected in the coagulation profile of children aged 1–5 years (Tables 3, 4). In the follow-up period after COVID-19, this age group had the highest number of abnormalities: thrombocytosis persisted (p = 0.02), platelet aggregation (p < 0.001) and aPTT were decreased (p < 0.01), euglobulin lysis time (p < 0.01) and D-dimer (p < 0.001) were still increased.

 

Table 4

Coagulation parameters in children in the post-COVID-19 period (Days 131.8 ± 10.05), M ± m

Parameter	Age, years
	1–5			6–10			11–18
	Test group, n = 15	Control group, n = 42	p	Test group, n = 17	Control group, n = 34	p	Test group, n = 20	Control group, n = 37	p
Platelets, 109/L	390.92 ± 37.23	323.5 ± 9.95	p = 0.02	335.06 ± 60.11	307.1 ± 6.57		287.11 ± 34.19	270.3 ± 9.18
Platelet aggr., %	57.20 ± 3.54	65.8 ± 1.13	p < 0.001	56.88 ± 3.95	66.5 ± 1.46	p < 0.01	60.29 ± 20.86	64.9 ± 1.04
INR	0.99 ± 0.01	1 ± 0.01		2.02 ± 0.91	1 ± 0.008		1.94 ± 0.88	1.00 ± 0.01
aPTT, s	32.79 ± 1.12	35.8 ± 0.54	p < 0.01	33.08 ± 1.37	34.9 ± 0.53		35.60 ± 1.19	34.1 ± 0.56
Platelet time, s	17.87 ± 0.32	18.2 ± 0.17		17.66 ± 0.32	18.2 ± 0.162		18.63 ± 0.32	18.3 ± 0.12
Fibrinogen, g/L	2.79 ± 0.25	2.5 ± 0.07		3.58 ± 0.83	2.40 ± 0.055	p < 0.05	3.30 ± 0.80	2.5 ± 0.06
AT – III %	116.21 ± 4.58	109.5 ± 1.41		105.22 ± 6.74	106.60 ± 1.18		98.44 ± 4.69	105.3 ± 1.24
SFMC, nmol/L	5.37 ± 0.44	4.7 ± 0.16		6.34 ± 0.72	4.50 ± 0.176	p < 0.001	5.78 ± 0.76	5.2 ± 0.13
Euglobulin lysis, min	13.07 ± 1.75	9.5 ± 0.5	p < 0.01	12.94 ± 1.40	7.30 ± 0.244	p < 0.001	13.86 ± 3.43	7.00 ± 0.24	p < 0.01
D-dimer, μg/L	530.1 ± 134.2	188.7 ± 22.7	p < 0.001	670.0 ± 386.64	172.2 ± 18.64	p < 0.001	431.20 ± 154.83	211.58 ± 29.43	p < 0.001

 

In the coagulation profile of 6-10-year-old children again (as in the acute period of COVID-19), changes in the following parameters were found: decreased platelet aggregation (p < 0.01), increased fibrinogen (p < 0.05), increased SFMC (p < 0.001), and increased euglobulin lysis time (p < 0.001). Follow-up D-dimer levels after COVID-19 decreased compared to the acute period; however, they were significantly higher than in the control group (p < 0.001).

In children of the older age group (11–18 years), increased euglobulin lysis time (p < 0.01) and D-dimer (p < 0.001) persisted in the post-COVID-19 period.

Therefore, changes in the blood coagulation parameters were seen in all age groups of children 4–4.5 months after COVID-19 (Figure 2, a–c). Patients aged 1 to 5 years should get special attention. In young children, the proportions of patients with thrombocytosis (53 %), increased fibrinogen (20 %), increased SFMC (20 %), and decreased aPPT (40 %) were almost the same as at the onset of COVID-19 (52 %, 24 %, 28 %, and 44 %, respectively). A significant decrease in the percentage of children was seen only for euglobulin lysis (53 % in the post-COVID-19 period vs. 80% in the acute period) (see Figure 1, a, and Figure 2, a). The percentage of children with increased D-dimer levels also decreased (28 % vs. 13 %).

 

Fig. 2. Proportion of patients with changes in coagulation parameters in the post-COVID-19 period, %: a – children aged 1–5 years; b – 6–10 years; c – 11–18 years

 

In children aged 6–10 years, the proportion of patients with coagulation profile changes decreased. Thrombocytosis was recorded in 17.65 % of patients (vs. 27.6 % in the acute period of COVID-19), decreased platelet aggregation in 29.7 % (vs. 37.9 %), and high fibrinogen levels in 5.8 % (vs. 17.25 %). No abnormalities of aPPT were seen in the post-COVID-19 period, while they were seen in 34.5 % of patients in the acute period. The proportion of subjects with high euglobulin lysis time decreased (from 62.1 % to 41.2 %); the number of children with high levels of D-dimer decreased by almost 2 times (Figure 1, b, and Figure 2, b).

In patients aged 11–18 years, the proportion of children with coagulation abnormalities significantly decreased. The proportion of children with reduced platelet aggregation decreased from 51.3 % to 20 %; high fibrinogen levels in the post-COVID-19 period were seen only in 5 % of patients (vs. 51.3 %), high levels of SFMC in 20 % (vs. 53.9 %), and increased euglobulin lysis time in 30 % (vs. 65.8 %). No children had low aPTT (with 28.9 % during the acute period) (see Figure 1, c, and Figure 2, c).

Conclusions

Coagulation profiles of children in the acute period of COVID-19 showed quite serious changes in the hemostasis system, with the disturbances affecting all its components (i.e. vascular-platelet, plasma-coagulation, and fibrinolysis components), regardless of the severity of the infection. Changes in blood coagulation profile persisted 4–4.5 months after COVID-19.

Based on the data received, young children (1–5 years old) had the most concerning changes. Both at the onset of COVID-19 and in the post-COVID-19 period, these patients had the highest number and frequency of disturbances. Only this age group had their number of platelets increased; however, thrombocytosis in children is likely to be relative and occurs due to the redistribution of these cells in different regions of the vascular bed, which is especially common in vasculitis (and, in its turn, is concerning). In young children, the initial and follow-up examinations showed decreased aPTT, suggesting disturbed intrinsic coagulation pathway and increased coagulation. Such a coagulation profile in patients of 1–5 years old may be explained by the development stage of this age group body, i.e. not yet fully formed immune system, which is known to “control” all organs and systems, including the hemostasis system.

The most positive state of the blood coagulation system was seen in the older age group (children aged 11–18 years old). Although the onset of COVID-19 in children was associated with significant changes in hemostasis parameters, which was typical for COVID-19, almost all parameters reached their optimal values in the post-COVID-19 period. Euglobulin lysis time was the only exception because it still remained high (p < 0.01) (although decreased compared with the onset of the disease).

In children aged 6–10 years old, changes in coagulation profile were pronounced both in the acute and follow-up periods. The changes persisted in many parameters and in a significant number of patients even 4 to 4.5 months later.

The findings confirmed the opinion that coagulopathy is a complication of COVID-19 that can lead to thrombosis in large and small vessels, not only in the veins and pulmonary arteries but also in the heart, vessels of the brain, kidneys, and liver [7; 9; 22]. Thrombosis at various levels, including microvessels, leads to damage to many organs or multiple organ failure [2; 4; 20; 24]. Inhibition of fibrinolysis (hypofibrinolysis) may also be a predictor of thromboembolic complications. Children after COVID-19 are at risk of developing the above-mentioned complications, require closer attention, and should be followed up for at least 4–4.5 months after COVID-19 resolution.

About the authors

O. P. Kovtun

Ural State Medical University

Email: usma@usma.ru
ORCID iD: 0000-0002-4462-4179

DSc (Medicine), Professor, Academician of the Russian Academy of Sciences, Rector

Russian Federation, Yekaterinburg

O. M. Olenkova

Clinical and Diagnostic Center named after Ya.B. Beikin

Author for correspondence.
Email: dcldvir@mail.ru
ORCID iD: 0000-0001-7360-5535

PhD (Medicine), Head of the Laboratory of Virology

Russian Federation, Yekaterinburg

A. V. Leontieva

Clinical and Diagnostic Center named after Ya.B. Beikin

Email: dcldvir@mail.ru
ORCID iD: 0009-0005-6737-9945

Physician, Hemostasis Laboratory

Russian Federation, Yekaterinburg

References

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