ORIGINAL PAPER
Nagoya J. Med. Sci. 85. 310–318, 2023
doi:10.18999/nagjms.85.2.310

Fibcare® shows correlation with fibrinogen levels by
the Clauss method during cardiopulmonary bypass
Akihiro Yamada1, Takahiro Tamura1, Takahiro Imaizumi2,3,
Yoko Kubo4 and Kimitoshi Nishiwaki1
1
Department of Anesthesiology, Nagoya University Graduate School of Medicine, Nagoya, Japan
Center for Advanced Medicine and Clinical Research, Nagoya University Hospital, Nagoya, Japan3
Department of Nephrology, Nagoya University Graduate School of Medicine, Nagoya, Japan
4
Department of Preventive Medicine, Nagoya University Graduate School of Medicine, Nagoya, Japan
2

ABSTRACTCentral laboratory measurements are time consuming, while rapid fibrinogen level measurements
within the operating room improve transfusion strategies. We aimed to clarify the correlation between
fibrinogen concentrations (measured using Fibcare® and the Clauss fibrinogen assay in a central laboratory)
during cardiovascular surgery with cardiopulmonary bypass. Data of patients whose Fibcare, traditional
laboratory-based testing, and thromboelastographic results were measured using the same blood sample
during cardiopulmonary bypass from February 2021 to January 2022 were retrospectively examined. We
analyzed correlation in categories of body temperature during cardiopulmonary bypass: total cases, mild
hypothermia (28–34°C), and moderate or severe hypothermia (<28°C). The Clauss fibrinogen assay was
performed in 123 cases, Fibcare in 107, and thromboelastography in 91. For mild hypothermia, moderateor severe hypothermia, and overall, the root mean squared error and R-square in Fibcare were 16.1
and 0.86, 13.1 and 0.87, and 14.9 and 0.87, respectively, and for thromboelastography, they were 3.26
and 0.74, 2.70 and 0.79, and 3.08 and 0.75, respectively. A significant relationship was noted between
Fibcare and Claus fibrinogen analysis regardless of body temperature during cardiopulmonary bypass. The
measurement of fibrinogen levels using Fibcare allows for faster transfusion preparation than that of the
traditional Clauss fibrinogen assay.
Keywords: Fibcare, thromboelastography, platelet mapping, fibrinogen, cardiopulmonary bypass
Abbreviations:
CPB: cardiopulmonary bypass
TEG6s: thromboelastography
ActF-MA: maximum amplitude of activator f
This is an Open Access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
License. To view the details of this license, please visit (http://creativecommons.org/licenses/by-nc-nd/4.0/).

INTRODUCTION
Cardiovascular surgery with cardiopulmonary bypass (CPB) changes coagulation function
Received: April 25, 2022; accepted: July 25, 2022
Corresponding Author: Takahiro Tamura, MD, PhD
Department of Anesthesiology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku,
Nagoya 466-8550, Japan
Tel: +81-52-744-2340, Fax: +81-52-744-2342, E-mail: takahiro@med.nagoya-u.ac.jp
310Rapid prediction of fibrinogen levelby several mechanisms, such as hypothermia, acidosis, and induction of the inflammatorycascade.1-4 In addition, the decrease in coagulation factor activity during CPB is strongly related
to hemostasis after CPB cessation. Coagulopathy associated with massive bleeding has been
implicated particularly in the reduction of plasma fibrinogen levels.5 Maintenance of high levelsof coagulation factors, especially fibrinogen, is necessary for hemostasis during cardiovascularsurgery.6,7 Determination of fibrinogen concentration is important for hemostasis management,8and it is a general standard to keep the fibrinogen concentration above 150–200 mg/dL.
Devices such as thromboelastography (TEG6s®, Haemonetics Japan GK, Japan) have been
recommended to guide transfusion during cardiovascular surgery. 9-11 Measuring coagulation
function with these devices has been shown to improve transfusion outcomes in cardiovascularsurgery.12 These point-of-care tests have the advantage of bedside availability and immediate
results compared to conventional laboratory blood tests. It often takes at least 30–40 min to obtain
results of central laboratory measurements of plasma fibrinogen concentration,13 and delayedmeasurement leads directly to delayed hemostasis management. Therefore, rapid monitoring ofhemostatic coagulability is necessary. We previously reported a study of rapid estimation offibrinogen concentrations using TEG6s during CPB.14 However, the measurement cartridge of
TEG6s, Platelet Mapping, is expensive and is not suitable for multiple measurements due toits cost.
Fibcare® (Atom Medical Co, Tokyo, Japan) is a monitor that can measure plasma fibrinogenlevels in approximately 2 min, and Okahara et al and Imai et al reported a correlation between
Fibcare and blood collection15 and within the obstetric field,16 respectively. However, there havebeen no reports evaluating Fibcare and central laboratory results in relation to body temperaturein patients undergoing extracardiac cardiopulmonary bypass and receiving heparin. If Fibcare
can accurately determine the fibrinogen concentration during CPB, including in heparinized andhypothermic patients, it would help in the effective management of post-CPB coagulopathy andbleeding. The purpose of this study was to clarify the correlation between fibrinogen concentration as measured by Fibcare and the Clauss fibrinogen assay in a central laboratory during
cardiovascular surgery with CPB in our institution.

METHODS
Study design and data collection
This study adhered to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. Additionally, this single-center retrospective observational study
conforms to the standards of the Declaration of Helsinki and was approved by the ethics committee of Nagoya University Hospital (approval number: 2021–0456; application for a change of
period has been filed for a change of the target period). Individual informed consent was obtained
from the patients using an opt-out method of enrollment via the hospital’s website. Patients who
were scheduled for cardiac or aortic surgery with CPB from February 2021 to January 2022, andwith the Clauss fibrinogen assay in the central laboratory and Fibcare or maximum amplitude ofactivator f (ActF-MA) by TEG6s measurements on blood samples taken simultaneously during
CPB, were enrolled. In short, the patients had only one Clauss measurement and only one
Fibcare or ActF-MA measurement or both, and multiple blood samples were not collected fromthe same patient. The primary analysis item was the correlation between fibrinogen concentration
as measured by Fibcare and the Clauss fibrinogen assay. We reexamined the correlation between
ActF-MA, a previously reported rapid diagnostic method,14 and the Clauss method for comparison
with the primary endpoint. In addition, the height, weight, age, sex, and body temperature were
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Akihiro Yamada et al

extracted during CPB.
Standard monitoring for cardiovascular surgery patients (non-invasive arterial blood pressure
measurements, electrocardiography, pulse oximetry, bispectral index monitoring, radial arterycannulation, and pulmonary artery catheterization) was performed in all patients. Fentanyl andmidazolam were administered intravenously to induce general anesthesia. Remifentanil androcuronium were additionally used to facilitate tracheal intubation, and general anesthesia wasmaintained with air, oxygen, remifentanil, and volatile anesthetics. Porcine heparin (300 U/kg) was
administered before starting cannulation for CPB, and additional heparin boluses (50 U/kg) wereadministered to maintain an activated clotting time of at least 400 s. Ventilation was re-started
before separating from CPB, and CPB was terminated with inotropic drug support. Protamine(3 mg/kg) was administered to antagonize the heparin effect, and the patient was intubated andadmitted to the intensive care unit. Red blood cell concentrates were transfused to maintain ahemoglobin level of >8 mg/dL during CPB. Coagulation function was monitored using a standard
TEG6s assay, and fresh frozen plasma and platelet concentrate were administered appropriately.
Blood sampling and measurement protocols
Blood samples of 6.4 mL were collected via a radial artery cannula system with a closed
circuit for blood sampling during CPB and were collected to obtain results at the same time

Fig. 1 Blood sampling
The sampling point was between the end of surgical procedure and HOT shot of cardio-plegia. In each patient,
6.4 mL blood sample was collected once, 2.7 mL was used for the Clauss method, 2.7 mL for Fibcare, and 1
mL for ActF-MA measurement. Traditional laboratory-based testing was used to measure fibrinogen concentration;
specimens were submitted to our hospital’s central laboratory and measured by the laboratory technician using
Clauss fibrinogen assay. Fibcare was used to measure fibrinogen concentration, and ActF-MA was used to predict
the fibrinogen concentration in the operating room.
CPB: cardiopulmonary bypass
HOT: warm blood cardioplegia
ActF-MA: maximum amplitude of activator f
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Rapid prediction of fibrinogen level

points for fibrinogen concentration measurements for Fibcare, fibrinogen concentration measurements for our hospital’s central laboratory, and ActF-MA. Fibcare was used to measurefibrinogen concentration, and ActF-MA was used to predict the fibrinogen concentration in theoperating room. Traditional laboratory-based testing was used to measure fibrinogen concentration;
specimens were submitted to our hospital’s central laboratory and measured by the laboratory
technician using Clauss fibrinogen assay (Analyzer: CN-6000; measuring reagent: Thrombocheck
Fib [L], Sysmex Corporation, Kobe, Japan). Fibcare has a lower and upper limit of 80 and 300,
respectively. If the result was <80, a value of 40 was imputed, while if the result exceeded theupper limit, the result was excluded from the analysis. ActF-MA by TEG6s has a lower limitof 2.0. If the result was <2.0, a value of 1.0 was imputed.
Statistical analyses
We evaluated the correlation between fibrinogen concentration via traditional laboratory-based
testing by Clauss fibrinogen assay and Fibcare using Deming regression analysis. The correlation
was analyzed in three categories of body temperature evaluated during CPB: mild hypothermia(28–34°C), moderate or severe hypothermia (below 28°C), and total patients.17 We also examinedthe correlation between Clauss fibrinogen assay and TEG6s under the same temperature conditions. Robust regression detected outliers (Cook’s distance >1), and Deming regression determined
the slope and intercept of the linear prediction equation. Root mean squared error was obtained
from Deming regression and R-square was obtained from ordinary least square. We performed
1000 bootstrap resampling to obtain the confidence intervals for root mean squared error and Rsquare. All analyses were performed using Stata 17 MP (Stata Corp, College Station, TX, USA).

RESULTS
Between February 2021 and January 2022, 123 patients were enrolled in the study. Patient
information and surgical characteristics are shown in Table 1. Blood samples were collected once
Table 1

Demographic and surgical characteristics
Total (n = 123)

Milda (n = 76)

Moderate or severea (n = 47)

Age (years)

65.33 ± 13.89

64.09 ± 14.36

67.32 ± 12.86

Height (cm)161.66 ± 8.83

160.99 ± 8.45

162.74 ± 9.31

Body weight (kg)62.16 ± 12.72

58.28 ± 11.24

60.11 ± 13.80

Body mass index (kg/m2)

23.86 ± 3.83

22.09 ± 3.01

22.48 ± 3.57

86:37

52:24

34:13

Anesthesia time

409.09 ± 134.54

393.70 ± 127.38

433.98 ± 141.87

Surgical time

326.05 ± 124.67

312.97 ± 118.10

347.19 ± 131.91

CPB time

167.62 ± 67.61

160.77 ± 61.44

178.60 ± 75.18

Minimum nasal temperature during CPB

28.62 ± 5.55

32.62 ± 1.86

22.57 ± 3.36

Minimum vesical temperature during CPB

31.83 ± 4.24

33.50 ± 1.50

29.13 ± 5.62

Minimum skin temperature during CPB

25.93 ± 3.23

25.61 ± 3.17

26.45 ± 3.26

Males:females
Surgical characteristics

Data are presented as mean ± standard deviation or as number (of patients), as appropriate.
The correlation was analyzed in three categories of body temperature evaluated during CPB with: mild hypothermia(28–34°C); moderate or severe hypothermia (<28°C); and total patients.
CPB: cardiopulmonary bypassaNagoya J. Med. Sci. 85. 310–318, 2023

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Akihiro Yamada et al

Fig. 2 Relationship between Fibcare and the Claus fibrinogen assay
Fibcare was measured in 107 cases with 66 of mild hypothermia and 41 of moderate or severe hypothermia.
The correlation between fibrinogen concentration via Fibcare and the Clauss fibrinogen assay was evaluated using
Deming regression analysis.
Fig. 2a: Relationship between Fibcare and the Claus fibrinogen assay in total cases (n=107). Fibrinogen Prediction Equation, RMSE, and R-square are 1.02×Fibcare -4.47, 14.9 [12.7–17.1], and 0.87 [0.83–0.91],
respectively.
Fig. 2b: Relationship between Fibcare and the Claus fibrinogen assay in mild hypothermia cases (n=66).
Fibrinogen Prediction Equation, RMSE, and R-square are 1.02×Fibcare -3.18, 16.1 [13.1–19.0], and0.86 [0.80–0.92], respectively.
Fig. 2c: Relationship between Fibcare and the Claus fibrinogen assay in moderate or severe hypothermia cases(n=41). Fibrinogen Prediction Equation, RMSE, and R-square are 1.04×Fibcare -7.11, 13.1 [10.0–16.2],
and 0.87 [0.80–0.95], respectively.
RMSE: root mean squared error

at the same time point from each patient for measuring the Clauss fibrinogen assay and Fibcare
and/or TEG6s. The Clauss fibrinogen assay was measured in all cases. Fibcare was measured in
107 cases with 66 of mild hypothermia and 41 of moderate or severe hypothermia. ActF-MA wasmeasured in 91 cases with 55 of mild hypothermia and 36 of moderate or severe hypothermia.
Values measured with the Clauss fibrinogen assay and those measured with Fibcare aredemonstrated in Figure 2a (total), Figure 2b (mild hypothermia), and Figure 2c (moderate orsevere hypothermia). Values measured with the Clauss fibrinogen assay and those measured with
ActF-MA are demonstrated in Figure 3a (total), Figure 3b (mild hypothermia), and Figure 3c(moderate or severe hypothermia). No case was excluded in the Robust regression, ie, there wasno outliers in both assays.
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Rapid prediction of fibrinogen level

Fig. 3 Relationship between ActF-MA and the Claus fibrinogen assay
ActF-MA was measured in 91 cases with 55 of mild hypothermia and 36 of moderate or severe hypothermia.
The correlation between fibrinogen concentration via Fibcare and the Clauss fibrinogen assay was evaluated using
Deming regression analysis.
Fig. 3a: Relationship between ActF-MA and the Claus fibrinogen assay in total cases (n=91). Fibrinogen Prediction Equation, RMSE, and R-square are 11.7×ActF-MA +83.5, 3.08 [2.64–3.52], and 0.75 [0.68–0.82],
respectively.
Fig. 3b: Relationship between ActF-MA and the Claus fibrinogen assay in mild hypothermia cases (n=55).
Fibrinogen Prediction Equation, RMSE, and R-square are 12.5×ActF-MA +78.9, 3.26 [2.67–3.85], and0.74 [0.65–0.82], respectively.
Fig. 3c: Relationship between ActF-MA and the Claus fibrinogen assay in moderate or severe hypothermia
cases(n=36). Fibrinogen Prediction Equation, RMSE, and R-square are 9.84×ActF-MA +93.4, 2.70
[2.19–3.21], and 0.79 [0.69–0.90], respectively.
ActF-MA: maximum amplitude of activator f
RMSE: root mean squared error

The values of root mean squared error and R-square are shown in Table 2. The results of
Fibcare were 14.9 [12.7–17.1] and 0.87 [0.83–0.91] in total, 16.1 [13.1–19.0] and 0.86 [0.80–0.92]
in mild hypothermia cases, and 13.1 [10.0–16.2] and 0.87 [0.80–0.95] in moderate or severe
hypothermia cases. The results of ActF-MA were 3.08 [2.64–3.52] and 0.75 [0.68–0.82] in total,
3.26 [2.67–3.85] and 0.74 [0.65–0.82] in mild hypothermia cases, and 2.70 [2.19–3.21] and 0.79
[0.69–0.90] in moderate or severe hypothermia cases.

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Table 2
Measurement

Root mean squared error and R-square

Fibrinogen Prediction Equation

RMSE

R-squareTotal

1.02×Fibcare – 4.47

14.9 [12.7–17.1]

0.87 [0.83–0.91]

Mild

1.02×Fibcare – 3.18

16.1 [13.1–19.0]

0.86 [0.80–0.92]

Moderate or severe

1.04×Fibcare – 7.11

13.1 [10.0–16.2]

0.87 [0.80–0.95]

11.7×ActF-MA + 83.5

3.08 [2.64–3.52]

0.75 [0.68–0.82]

FibcareActF-MA
Total
Mild

12.5×ActF-MA + 78.9

3.26 [2.67–3.85]

0.74 [0.65–0.82]

Moderate or severe

9.84×ActF-MA + 93.4

2.70 [2.19–3.21]

0.79 [0.69–0.90]

Data are presented as mean ± standard deviation or as number (of patients), as appropriate.
The correlation was analyzed in three categories of body temperature evaluated during CPB with: mild hypothermia(28–34°C); moderate or severe hypothermia (<28°C); and total patients.
CPB: cardiopulmonary bypass
ActF-MA: maximum amplitude of activator f
RMSE: root mean squared error

DISCUSSION
This study analyzed the correlation between fibrinogen concentration via traditional laboratorybased testing by Clauss fibrinogen assay and Fibcare. The results of this study revealed that
Fibcare results strongly predict fibrinogen concentration during CPB, whether during hypothermia
or not. In addition, the results of this study showed that more accurate blood concentration prediction was possible than with the rapid diagnosis method (ActF-MA) that we proposed until now.
Fibrinogen replacement therapy for hemostasis can be managed by transfusion of fresh frozen
plasma, cryoprecipitate, and fibrinogen concentrate. Some guidelines have suggested the use oftransfusion to maintain a target fibrinogen concentration above 150 mg/dL.18-21 Therefore, forhemostatic coagulation management, it is important to know the fibrinogen concentration after
discontinuing CPB. However, it can take 40–60 min for traditional fibrinogen concentration
measurement assays to report test results. Therefore, if fibrinogen concentration during CPB
can be quickly determined using Fibcare, which provides results in approximately 2 min, rapid
coagulation management is possible. Our results clearly indicate that measurement of fibrinogenlevels using Fibcare allows for faster transfusion preparation than the traditional Clauss fibrinogenassay.
We previously reported a significant relationship between ActF-MA and the Clauss fibrinogenassay.14 In ActF-MA, fibrinogen reaction occurs through reptilase, an enzyme found in thevenom of snakes such as the Fer de lance; fibrinogen is converted to fibrin, and stabilization of
the fibrin is facilitated by activated factor XIII and composes what has been called activator f.
Thus, ActF-MA does not directly measure fibrinogen levels because it activates fibrin formation
using a thrombin-free pathway. Fibcare and the CG02N coagulation analyzer (A&T, Kanagawa,Japan) are based on the same principle: an improved device based on CG02N using the dryhematology system by measuring whole blood. CG02N requires diluting blood samples with asolution manually, and there is a risk of error during the measurement process. For this reason,
rapid measurement is difficult during cardiovascular surgery with CPB. In contrast, Fibcare does
not require diluting blood samples, and thus concentrations can be measured rapidly. Reports
examining the accuracy of CG02N in cardiovascular surgery have shown that plasma fibrinogenlevels can be accurately measured even in CPB cases, and that the dry hematology method is
not affected by dilution or heparin administration.22
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Rapid prediction of fibrinogen level

Fibcare is also attractive because of the lower cartridge cost per measurement of ActF-MA:
approximately USD 10 per Fibcare cartridge in comparison to USD 100 per TEG6s cartridge.
TEG6s was not originally designed to directly measure fibrinogen concentration. These devices
are used to measure comprehensive coagulation functions, including coagulation factors, platelets,and fibrinogen; to determine the need for transfusions such as fresh frozen plasma and plateletconcentrate; and/or to conduct post-transfusion assessment of coagulation functions.9-11 For thisreason, it would be advantageous to utilize the inexpensive Fibcare in order to quickly determine
the fibrinogen value only.
This study has substantial limitations that should be addressed. First, as can be determinedfrom measured values, the prediction equation is not absolute, and variations exist. Even theClauss fibrinogen assay can have different results at different institutions. However, variationsin Fibcare results and correlations may be considered acceptable in clinical practice and do notcreate a problem for the rapid determination of fibrinogen concentrations in the range >200
mg/dL, 150–200 mg/dL, or <150 mg/dL. Second, fibrinogen concentration is most commonlymeasured using the Clauss fibrinogen assay. However, instruments such as coagulation analyzers
and thrombin reagents are not well standardized between hospitals. A previous study showed thatfibrinogen concentration measured by the Clauss fibrinogen assay varies considerably between
hospitals.23 For this reason, our findings may differ in another hospital. Further multicenter studies
are needed to evaluate our findings in order to eliminate bias at each center and to evaluate theassociation with the Clauss fibrinogen assay.
In summary, our results show a significant relationship between Fibcare and the Clauss
fibrinogen assay. Low fibrinogen concentration can be estimated more quickly by Fibcare thanby traditional methods, and Fibcare allows fast prediction of fibrinogen concentration and rapidtransfusion preparation in cardiac surgery.

ACKNOWLEDGMENTS
We thank all the anesthesiology medical staff members and extra-corporeal technology staff
members of Nagoya University Hospital.

DISCLOSURE STATEMENT
None of the authors has any conflicts of interest to declare in relation to this work.

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