doi: 10.2169/internalmedicine.9150-17Intern Med 57: 393-397, 2018
http://internmed.jp【 CASE REPORT 】

High Titer of Acquired Factor V Inhibitor Presenting witha Pseudo-deficiency of Multiple Coagulation Factors
Keiichi Nakata 1, Shuji Ueda 1, Hitomi Matsunaga 1, Fuka Mima 1, Hiroki Ueda 1,
Aya Yoshioka 2, Sayoko Kaneko 2, Kazushi Maruo 3, Shayne Morris 4, Sayoko Yonemoto 1,
Daisuke Hayashi 1, Naohiko Fujii 1, Hiroyuki Narahara 1, Yoshiaki Inui 1 and Sumio Kawata 1

Abstract:
Acquired coagulation factor inhibitor is a rare coagulation disorder. We herein report a patient with acquired factor V inhibitor showing a decrease in multiple coagulation factor activities. A high titer of factor V
inhibitor presumably led to a marked inhibition of factor V activity in the specific factor-deficient plasmaused in coagulation factor activity assays based on either an activated partial thromboplastin time (APTT) or
prothrombin time (PT) clotting assay, resulting in false low values of the coagulation activity. We reexamined the coagulation factor activity using several dilutions of the patient’s plasma and confirmed that thehigh factor V inhibitor titer had caused an apparent decrease in multiple coagulation factor activities.
Key words: acquired factor V inhibitor, high titer inhibitor, APTT or PT based clotting assay(Intern Med 57: 393-397, 2018)(DOI: 10.2169/internalmedicine.9150-17)

Introduction
Factor V is a plasma cofactor that plays a pivotal role inthe blood coagulation cascade. Acquired factor V inhibitor isan uncommon bleeding disorder that can arise from various
conditions and diseases, especially exposure to bovine
thrombin or fibrin glue, the use of antibiotics, blood transfusion, autoimmune disorders, and malignancies (1). A diagnosis of factor V inhibitor is usually confirmed by measuring the factor V activity and the inhibitor titer, which are determined using a clotting assay and the Bethesda assay, respectively. We herein present a patient with acquired factor
V inhibitor who showed a decrease in the activity of multiple coagulation factors because of a very high factor V inhibitor titer.

Case Report
A 72-year-old Japanese woman was referred to our hospi-

tal by her general practitioner because of fatigue and nausea.
She had a history of chronic kidney disease (CKD) due tohypertensive nephrosclerosis. Under the management of her
local hospital, she was on treatment with a β-blocker, warfarin, diuretics, phosphate binders, and activated vitamin D
for hypertension, atrial fibrillation, and CKD. Although she
had stage 5 CKD, her renal function was stable with a serum creatinine level of about 5.5 mg/dL. On admission, herblood pressure was 148/108 mmHg. Non-contrast abdominal
computed tomography (CT) revealed a subcapsular crescentshaped high-density area in the left kidney that was consistent with a subcapsular renal hematoma (Fig. 1). She had no
history of renal trauma and no evidence of any renal neoplasm, so we considered that the subcapsular renal hematoma was likely a bleeding complication due to warfarintherapy (2). Laboratory tests showed an elevation of serum
C-reactive protein (CRP) and creatinine to 20.08 mg/dL and7.49 mg/dL, respectively. The platelet count was 134×109/L.
Routine coagulation tests revealed a prolongation of theprothrombin time to 20.8 seconds (international normalized

１

Department of Internal Medicine, Hyogo Prefectural Nishinomiya Hospital, Japan, ２ Department of Clinical Laboratory, Hyogo Prefectural
Nishinomiya Hospital, Japan, ３ Department of Medical Engineering, Hyogo Prefectural Nishinomiya Hospital, Japan and ４ Department of Neurosurgery, Hyogo Prefectural Nishinomiya Hospital, Japan
Received: March 7, 2017; Accepted: May 28, 2017; Advance Publication by J-STAGE: November 1, 2017
Correspondence to Dr. Shuji Ueda, ueda0904@hp.pref.hyogo.jp393

Intern Med 57: 393-397, 2018

DOI: 10.2169/internalmedicine.9150-17
Table 1.
mission.

Serial changes in the laboratory values after ad-

Time (days)
PT (sec)
INR
APTT (sec)Platelet (109/L)
Fib (mg/dL)
FDP (μg/mL)
D-dimer (μg/mL)
CRP (mg/dL)

Figure 1. Computed tomography revealed a subcapsular renal hematoma.

ratio: 1.72), but the activated partial thromboplastin time
(32.1 seconds) was within the normal range (24.0-35.0 seconds). The plasma levels of fibrin/fibrinogen degradation
products and D-dimer were slightly elevated to 11.5 μg/mL
and 3.7 μg/mL, respectively. Blood culture was performedon admission, and it was positive for Klebsiella pneumoniae.
Urine culture also yielded Klebsiella pneumoniae (>100.000
colonies) with the same antibiotic sensitivity profile. Intravenous ceftriaxone was initiated for the treatment of sepsis andurinary tract infection due to Klebsiella pneumoniae. The
subcapsular renal hematoma was thought to be due to theprolongation of the prothrombin time by her warfarin therapy, and she was treated conservatively by radiologicalfollow-up without suspending the warfarin dosage. She responded well to antibiotic therapy and CRP decreased rapidly. The subcapsular renal hematoma was stable. Two
weeks after admission, routine coagulation tests revealed a
prolongation of activated partial thromboplastin time
(APTT) in addition to prothrombin time (PT). As a result,warfarin was stopped and Vitamin K was started, however,her clotting parameters thereafter became worse. One monthafter admission, APTT significantly increased to 106.6 seconds and international normalized ratio (INR) remained at
2.64 (Table 1). She did not show any clinical evidence of
bleeding, except for the subcapsular renal hematoma. The
presence of an acquired coagulation factor inhibitor was suspected, so a cross-mixing test was performed using plasma
from the patient and from a healthy volunteer. In this test,
both the APTT and PT curves demonstrated an upwardly
convex shape (Fig. 2). Serological tests for anticardiolipin
antibodies and anti-β2 glycoprotein-I antibodies were negative. Serum protein electrophoresis did not show any abnormalities. We checked the full coagulation factor activity profile, including factor XIII (Table 2). The activity of factors
XII, XI, IX, and VIII involved in the intrinsic coagulation
pathway was undetectable, and the factor VII activity (extrinsic pathway) was found to have decreased to 20%. Factors X, V, and II (common coagulation pathway) had also
markedly decreased, with factor V being undetectable. On
the other hand, the factor XIII activity was normal. While
the factor XIII activity was measured by a synthetic substrate, the other coagulation factors were measured by

Warfarin stopped/Vitamin K started
1
16
17
22
↓

33

20.8
1.72
32.1
134
724.6
11.5
3.7
20.08

31.6
2.64
106.6
123
439.9
3.0
1.1
0.35

20.1
1.66
39.2
110

35.8
2.99
74.2

1.9
4.95

1.4

32.5
2.71
97.7
120

0.57

PT: prothrombin time, INR: international normalized ratio, APTT: activated partial thromboplastin time, FDP: fibrin/fibrinogen degradation products, CRP: C-reactive protein

APTT- or PT-based clotting assays. We thought that a hightiter of an inhibitor for one coagulation factor might also
completely inhibit that factor in the specific factor-deficient
plasma used for APTT- or PT-based clotting assays, leading
to false low levels of coagulation factor activity. In that case,if the patient’s plasma was sufficiently diluted, then the effect of the inhibitor would be reduced and the coagulation
factor activity would thus be corrected. To confirm our hypothesis, we re-examined the coagulation factor activity using three dilutions of the patient’s plasma (5-, 10-, and 15fold) (Table 3). Factor V activity remained undetectable withall dilutions, but the activity of the other coagulation factors
increased along with the dilution ratio. In addition, an inhibitor assay (Bethesda assay) detected an extremely hightiter of factor V inhibitor (102 Bethesda U/mL), while thetiters of the inhibitors for the other factors were low (3-11
Bethesda U/mL) (Table 4). As the Bethesda assay is also an
APTT- or PT-based test, the low titers of other inhibitors
were thought to be false results caused by the same mechanism as in the coagulation factor activity assays. Based onthese findings, we concluded that the patient had acquired
factor V inhibitor and that a very high titer of this inhibitor
had interfered with the assays of the other coagulation factors. We performed the hepaplastin test (HPT) and thethrombo test (TT) for confirmation. The results were in thenormal range (104% and 126%, respectively), indicating thatshe did not have any deficiency of factors II, VII, and X.
The patient did not have any apparent cutaneous or mucosal bleeding, such as petechial hemorrhage. Although the
inhibitor could be expected to disappear within a period ofmonths without inhibitor elimination therapy (1, 3, 4), theinitiation of hemodialysis was required due to advanced renal failure, which necessitated the creation of an arteriovenous fistula. To reduce the risk of bleeding associatedwith surgery, we considered that inhibitor elimination therapy was required (5). Treatment with oral prednisolone wasstarted at 30 mg/day, but the response was insufficient. We
added oral cyclophosphamide (50 mg/day) and also performed one session of plasma exchange before surgery,which was performed without any bleeding complica-

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APTT

(sec)
120

3.0

100

2.5

80

2.0

60

1.5

40

1.0

20

0.5

Patient plasma 100
Normal plasma
0

80
20

50
50

PT

(INR)

20
80

0%
100 %

100
0

80
20

50
50

20
80

0%
100 %

Figure 2. Cross-mixing tests. The APTT and PT values showed upwardly convex curves, indicating
the presence of an inhibitor. APTT: activated partial thromboplastin time, PT: prothrombin time

Table 2.

Table 3. Coagulation Factor Activities
Assayed with Various Dilutions of Patient
Plasma.

Coagulation Factor Activities in Our Patient.

Coagulation factor

Activity (%)

Method

XII
XI
IX
VIII

<3
<3
<1
<1

APTT-based clotting assay

VII

20

X
V
II

11
<3
7

PT-based clotting assay

XIII

107

Synthetic substrate assay

APTT: activated partial thromboplastin time, PT: prothrombin time

Table 4. Coagulation Factor Inhibitors
in Our Patient.
Coagulation factor

Inhibitor (BU/mL)

XII
XI
IX
VIII
VII
X
V
II

7
7
7
7
3
4
102
11

tions (6). Subsequently, prednisolone was tapered as the factor V inhibitor level declined (Fig. 3).

Discussion
Coagulation factor activity other than factor XIII is usually evaluated by APTT-based (VIII, IX, XI, and XII) or PTbased (II, V, VII, and X) one-stage clotting assays. In theseassays, the coagulation factor activity is measured by assessing the ability of patient plasma to normalize the prolonged
clotting time of specific factor-deficient plasma (7). For example, if patient plasma is added to factor VIII-deficient
plasma and the APTT remains prolonged, this is taken to indicate that the patient has a factor VIII deficiency. However,

X1

X5

X10

X15

XII
XI
IX
VIII

<3%
<3%
<1%
<1%

<3%
<3%
<1%
2%

4%
6%
11%
13%

8%
7%
16%
22%

VII
X
V
II

15%
6%
<3%
4%

17%
9%
<3%
4%

29%
13%
<3%
9%

33%
14%
<3%
10%

there is a potential pitfall in the interpretation of such coagulation factor tests. If an extremely high titer of a coagulation factor inhibitor is present in the plasma (factor V inhibitor in the present patient), this large excess of such an
inhibitor will completely inhibit factor V in plasma that is
specifically deficient for other factors and the prolonged
clotting time will not be corrected, leading to a misdiagnosis
of deficiency even though the activity of the other factors isnormal. When coagulation factor activity assays are performed, patient plasma is usually diluted 10-fold before being added to specific factor-deficient plasma in order toavoid this phenomenon. However, the plasma of our patient
had an extremely high factor V inhibitor titer and the inhibitor still blocked factor V in specific factor-deficient plasma
after 10-fold dilution, and, as a result, the various assays
gave false low results.
To avoid this problem, another method can be used to determine the specific coagulation factor activities based on
the cleavage of specific chromogenic substrates by activatedfactors (7). Chromogenic substrate assays are available forseveral coagulation factors (including factors VIII, IX, andX), but it is difficult or impossible to obtain these for all of
the coagulation factors.
Our patient showed a marked decrease in the activity ofmultiple coagulation factors. We concluded that an excessively high titer of factor V inhibitor had blocked the factor

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plasmaexchangearteriovenous
fistula creation

hemodialysis
5mg

50mg

CPA

120

APTT (sec)

15mg

30mg

2.5

PT

90

2.0
60

APTT

1.5

30

PT (INR)PSL

1.0

FV inhibitor(Bethesda U/ml)

120
80
40
0

㻠㻜

Figure 3.

60

80

100

Time(days)

Clinical course of our patient with an acquired factor V inhibitor.

V activity in various specific factor-deficient plasma samples, thereby preventing the normalization of the prolonged
clotting time, although the patient actually had a normal activity of other coagulation factors. To confirm this, we performed the one-stage clotting assay after further diluting ourpatient’s plasma and the findings demonstrated that the factor V inhibitor had caused a reduction of multiple coagulation factor activities.
To the best of our knowledge, there have been only twocase reports of patient with acquired coagulation factor inhibitor showing a decrease in the activity of multiple coagulation factors, and the mechanisms underlying such abnormal laboratory findings have not been verified (8, 9). In
contrast, we clearly demonstrated that performing coagulation factor activity assays by carrying out several dilutionsof patient plasma could provide more accurate results. Bothof the previously reported patients also had high titers of acquired factor V inhibitor. An inhibitor of factor V will affectboth APTT and PT, and a profound inhibition of factor V
can influence the assay for any coagulation factor, except
factor XIII. There is also another interesting aspect to consider. In patients with factor V inhibitor, the bleeding tendency is characteristically mild and some patients do notshow any bleeding symptoms (3). This could be due to thefact that factor V is not only found in the plasma, but is also
stored in the alpha granules of platelets (10). Thus, plateletderived factor V might play a local hemostatic role at sitesof vascular injury. Despite having a very high titer of factor
V inhibitor, our patient did not develop any bleeding symptoms throughout the clinical course. It is possible that thelack of bleeding allowed the inhibitor titer to rise to such ahigh level.
However, there have been some reports of patients with ahigh inhibitor titer who did not develop a pseudo-deficiencyof multiple coagulation factors (11). Coagulation factor inhibitors are classified as type 1 or type 2 based on reaction

kinetics. An inhibitor with type 1 kinetics completely inactivates the target coagulation factor and there is a linear relationship between the logarithm of the residual coagulation
factor activity and the inhibitor concentration. On the other
hand, an inhibitor with type 2 kinetics does not completely
inactivate the target coagulation factor and there is a nonlinear relationship between the residual coagulation factor activity and the antibody concentration (12, 13). Even in thepresence of a high titer of a type 2 inhibitor, minimal coagulation factor activity might persist. This difference of inhibitor properties might be related to whether or not the patients develop a pseudo-deficiency of multiple coagulation
factors.
In the present case, the HPT and TT were useful for confirming the presence of a factor V deficiency. The HPT and
TT comprehensively show the activity of factors II, X, andVII, while the PT evaluates factors II, V, X, VII, and I (fibrinogen). Therefore, a prolonged PT together with normal
values for fibrinogen, HPT, and TT indicates a factor V deficiency. Combining these coagulation screening tests is thus
considered to be useful for diagnosing factor V deficiency (14).
The reason why our patient developed factor V inhibitor
remains unclear. We confirmed that she had not been exposed to bovine thrombin by a careful review of her medical
history. She also had no indicators or symptoms of malignancy or autoimmune disease. It is possible that ceftriaxone
had played a causative role in the development of our patient’s inhibitor. Because our patient needed shunt surgery,she was treated with immunosuppressive therapy and plasma
exchange despite the absence of any bleeding symptoms,
eventually resulting in the disappearance of the acquired inhibitor.
The authors state that they have no Conflict of Interest (COI).

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DOI: 10.2169/internalmedicine.9150-17

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Intern Med 57: 393-397, 2018397