Significantly Prolonged Prothrombin Time and Activated Partial Thromboplastin Time with no Bleeding Tendency: A Patient with Lupus Anticoagulant–Hypoprothrombinemia Syndrome Positive for Immunoglobulin M Anti-Phosphatidylserine/Prothrombin complex Antibodies

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of antiphospholipid antibodies. There are a wide variety of thrombophilic clinical symptoms in APS, including recurrent arterial and/or venous thrombotic events and recurrent fetal loss.[1] Lupus anticoagulant–hypoprothrombinemia syndrome (LAHPS) is a rare acquired disorder caused by prothrombin antibodies, which is suspected when a patient presents with bleeding and a prolonged activated partial thromboplastin time (APTT) and prothrombin time (PT) in combination with a lupus anticoagulant (LA).[2] We report a case of a patient with LAHPS whose plasma APTT and PT testing appeared to mainly be interfered by immunoglobulin M (IgM) antiphosphatidylserine/prothrombin (aPS/PT) complex antibodies.

A 58-year-old female complained of repeated dizziness and fatigue for 9 months after a cold. She presented to the hospital for the treatment of an oral ulcer that developed 2 months previously. Examination results were as follows: hemoglobin level of 53 g/L (normal: 115–150 g/L), direct antihuman globulin test as ++ + , Epstein–Barr (EB) virus nucleic acid quantification of 2.86 × 10⁴, oral ulcer secretion revealing Staphylococcus aureus, and blood culture revealing Pseudomonas aeruginosa. Bone marrow biopsy showed a decrease in bone marrow hematopoietic cells and megakaryocytes, which accorded with anemia-induced bone marrow image. No abnormalities in clonal structure or number were found in chromosome typing. Positron emission tomography–computed tomography (PET-CT) examination suggested a systemic lymph node inflammatory reaction. She was admitted to the hospital with “anemia with EB virus infection.”

She then underwent several examinations including complete blood count and leukocyte differential count tests, routine chemistry tests, and inflammation-related tests. There were a large number of abnormal test results identified, as shown in [Table 1]. The main details are as follows: pancytopenia (reduced leukocytes, erythrocytes, hemoglobin, platelets), normal alanine aminotransferase, and aspartate aminotransferase with slightly reduced albumin and globulin; bilirubin was slightly increased and urea and creatinine were normal, but lactate dehydrogenase and N-terminal probrain natriuretic peptide were increased, with inflammation reaction evident with elevated high-sensitivity C-reaction protein, interleukin-6, procalcitonin, and serum ferritin. Hepatitis B, human immunodeficiency virus, and syphilis tests were all negative, as were antinuclear antibodies and other autoantibodies. No abnormalities were observed in routine stool and urine examinations, as well as erythrocyte sedimentation rate.

Table 1 Results of routine laboratory examination with abnormal test results

Assays	Results	Reference intervals
Complete blood count and leukocyte differential count tests
Leukocytes, ×109/L	2.65	3.50–9.50
Neutrophils, %	84.9	40–75
Lymphocytes, %	7.2	20–50
Lymphocytes, ×109/L	0.19	1.10–3.20
Erythrocytes, ×1012/L	2.05	3.80–5.10
Hemoglobin, g/L	68	115–150
Hematocrit, %	22.3	35–45
Mean corpuscular volume, fl	108.8	82–100
Coefficient of variation of red blood cell distribution width, %	30.5	< 14.9
Standard deviation of red blood cell distribution width, fl	111.6	39–46
Platelets, ×109/L	85	125–350
Routine chemistry tests
Total protein, g/L	45.4	64–83
Albumin, g/L	29.2	35–52
Globulin, g/L	16.2	20–35
Total bilirubin, μmol/L	22.3	≤ 21
Direct bilirubin, μmol/L	10.5	≤ 8
Creatinine, μmol/L	38	45–84
Lactate dehydrogenase, U/L	308	135–214
N-terminal probrain natriuretic peptide, pg/mL	736	< 247
Inflammation-related tests
High-sensitivity C-reaction protein, mg/L	34.6	> 10 indicates possible infection
Interleukin-6, pg/mL	34.9	< 7
Procalcitonin, μg/L	0.09	0.02–0.05
Serum ferritin, μg/L	956	15–150

Coagulation testing ([Table 2]) revealed a prolonged PT (STA Neoplastine CI, Diagnostica Stago) and APTT (STA PTT Automate 5; Diagnostica Stago). Unexpectedly, the thromboelastogram (TEG) (TEG Hemostasis System Kaolin, Haemonetics Co.) results were basically normal, and there was no bleeding tendency reported by the patient. Thus, a series of subsequent hemostasis examinations were performed in the laboratory to explore the causes of this paradox, the findings of which are shown in [Table 2]. APTT did not correct with a 1:1 mixture of patient plasma and normal plasma and was more prolonged than the result from the patient plasma alone. In addition, the Rosner index ([APTT mixed – APTT standard]/ APTT patient] × 100) was much more than 15%, consistent with the presence of an inhibitor.

Table 2 Results of hemostasis assays

Assay	Result	Reference intervals
PT, seconds	29.5	11.5–14.5
INR	2.8	0.8–1.2
Prothrombin activity, %	28	75–125
APTT, seconds	85	29–42
APTT on 1:1 mix, seconds	104.1	NA
Rosner index[a]	55.4	NA
TT, seconds	14.5	14–19
Fibrinogen, g/L	2.65	2–4
D-dimer, μg/mL FEU	1.55	< 0.5
TEG
Reaction time (R), minutes	4.5	4–9
Clot formation time (K), minutes	1.7	1–3
Angle (α), degrees	73.3	58–78
Maximum amplitude, mm	49.6	50–70
EPL, %	0	0–15
CI	0.3	–3 to 3
LY30, %	0	0–5
SCT
SCT screen ratio	1.57	< 1.2
SCT confirm ratio	1.98	< 1.2
SCT normalized ratio	0.79	< 1.2
dRVVT
dRVVT screen ratio	1.35	< 1.2
dRVVT confirm ratio	0.98	< 1.2
dRVVT normalized ratio	1.38	< 1.2
Factor assay
VIII using 1:10 dilution and 1:80 dilution, %	1; 32	60–150
IX using 1:10 dilution and 1:80 dilution, %	1; 8	60–150
XI using 1:10 dilution and 1:80 dilution, %	2; 8	60–150
XII using 1:10 dilution and 1:80 dilution, %	2; 8	50–150
II using 1:10 dilution and 1:80 dilution, %	32; 32	70–120
V using 1:10 dilution and 1:80 dilution, %	50; 50	70–120
VII using 1:10 dilution and 1:80 dilution, %	63; 64	55–170
X using 1:10 dilution and 1:80 dilution, %	58; 56	70–120
Protein S, %	43	55–123
Protein C, %	56	70–142
ACL antibodies
IgA, CU	3	< 20
IgG, CU	2.6	< 20
IgM, CU	3.8	< 20
anti-B2GP1 antibodies
IgA, CU	< 4	< 20
IgG, CU	< 6.4	< 20
IgM, CU	< 1.1	< 20
aPS/PT complex antibodies[b]
IgG	Negative	Negative
IgM	Positive	Negative

Abbreviations: ACL, anticardiolipin; anti-B₂GP1, anti-β-2 glycoprotein 1; aPS/PT, antiphosphatidylserine/prothrombin; APTT, activated partial thromboplastin time; CI, comprehensive index; EPL, estimated percentage of lysis; dRVVT, diluted Russell viper venom time test; IgA, immunoglobulin A; IgG, immunoglobulin G; IgM, immunoglobulin M; INR, international normalized ratio; LY30, lysis at 30 minutes; NA, not applicable (see text); PT, prothrombin time; SCT, silica clotting time; TEG, thromboelastogram; TT, thrombin clotting time.

Note: Bold values indicate abnormal or raised values.

^a >15 suggests the presence of coagulation inhibitors such as anticoagulants, antiphospholipid antibodies, and coagulation factor antibodies; 11–15 equivocal; and < 11 suggests coagulation factor deficiency.

^b This is a qualitative test.

Coagulation factors were assessed by standard one-stage clotting assays (STA Factor deficient plasma, Diagnostica Stago) using dilutions of 1:10 and 1:80 to assess nonparallelism. Nonparallelism was observed in APTT-based factors (VIII, IX, XI, and XII) but not in PT/common pathway-based factors (II, V, VII, and X). The proposed interference responsible for this effect could not be overcome even when the dilution multiple was increased (i.e., 1:80 dilution). Additionally, the activity of factor II was markedly low (32%).

As the prolonged APTT could not be corrected with a 1:1 mixture of patient plasma and normal plasma, and as a significant inhibitory effect was observed on APTT-based factors, it seemed that a strong but nonspecific intrinsic pathway factor inhibitor was interfering with testing (i.e., LA). LA represents antibodies that inhibit phospholipid-dependent clotting times in a nonfactor specific manner.[1] Although the presence of LA can prolong PT and APTT in vitro, patients do not normally tend to suffer bleeding symptoms. However, sometimes bleeding tendency occurs if accompanied by severe thrombocytopenia and/or hypoproteinemia.[2] [3] In contrast, in vivo complexes of LA and phospholipid proteins can interfere with the activation of protein C and compete with active protein C/protein S complexes on the surface of phospholipids, resulting in inhibition in the inactivation of factors Va and VIIIa, which leads to a hypercoagulable state.[4] LA can also enhance platelet aggregation and inhibit fibrinolytic activity.[5] [6] Therefore, patients with LA positivity are prone to thrombosis and its complications, especially children and pregnant women.[7] [8] As no single test is sensitive for all LA, the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis recommends that two tests should be used to detect LA, and the recommended tests are the diluted Russell viper venom time (dRVVT) test and a sensitive APTT test.[9] Accordingly, we performed the dRVVT test (dRVVT Screen - 0020301500/ dRVVT Confirm - 0020301600, HemosIL, Instrumentation Laboratory Company) and the silica clotting time (SCT) test (Silica Clotting Time - 0020004800, HemosIL, Instrumentation Laboratory Company) in our case. The SCT is a form of APTT.[10] Results with the SCT test did not confirm the presence of LA with a negative normalized ratio (0.79; normal cutoff: < 1.20). However, the normalized ratio was 1.38 (normal cutoff: < 1.20) when dRVVT testing was performed, indicating the presence of LA. Anticardiolipin (ACL; QUANTA Flash Reagents, INOVA Diagnostics), and anti-β2-glycoprotein 1 (aβ₂GP1) (QUANTA Flash Reagents, INOVA Diagnostics), immunoglobulin A, immunoglobulin G (IgG), and IgM antibodies (Immunoglobulin Test Kit, Beckman Coulter Inc.) were all negative.

Taking the low activity of factor II (32%) and positive LA results into account, we propose that the diagnosis can be considered as LAHPS, although there were no evident bleeding symptoms according to the patient. Another paradox was the significant inhibitory effect observed on clotting factors by one-stage assay, APTT, and PT, given the low level of LA suggested by LA testing. Although, the laboratory criteria for the diagnosis of APS comprises only three tests (ACL IgG or IgM antibodies, anti-β₂GP1 IgG or IgM antibodies, and LA),[1] a positive finding with other antiphospholipid antibody tests may provide clarification of the diagnosis, although some seronegative antiphospholipid syndrome (SNAPS) patients have also been reported.[11] Accordingly, alternate antiphospholipid antibodies that have not been included in the APS diagnosis criteria have since been found in the “SNAPS” population, among which aPS/PT complex antibodies appear to be the most valuable of the new phospholipid antibodies.[12]

Bajaj et al originally reported antibodies in two patients with LAHPS, which encapsulate factor II without affecting their coagulation function, but the antibodies could accelerate the clearance of factor II.[13] This finding is consistent with the low activity of factor II in our case; thus, we tested for IgG and IgM aPS/PT complex antibodies (QUANTA Lite PS/PT ELISA kits, INOVA Diagnostics). Although IgG aPS/PT antibody was negative, the IgM antibody was positive. It therefore seems likely that the prolonged PT and APTT may be attributed to the interference of IgM antibody aPS/PT complex. This may also explain the conflicting results of the plasma coagulation test and TEG in this case. Thus, with in vitro plasma testing, aPS/PT complex antibodies can hinder the binding and activation of factor II with reagent phospholipids in the presence of calcium ions, leading to a significant prolongation of PT and APTT. Moreover, since the antibodies target the binding complexes of factor II and phospholipids, the addition of phospholipids alone cannot completely neutralize the antibodies. However, TEG, as a whole blood test, is mainly supplied with phospholipid on the surface of platelets, and therefore the antibodies would not appear as inhibitory and the results could be normal.

Another laboratory paradox that we observed was that the APTT using a 1:1 mixture of patient plasma and normal plasma was more prolonged than the patient plasma alone. This may have been due to some sort of hook effect, as described by Jin and Zehnder.[14] When the patient's plasma was mixed with normal plasma, the dilution of antibodies and the increase in factor II better “optimized” the antibody/antigen concentrations for the test system. As a result, a stronger inhibition was demonstrated. We later became aware of another study that showed that occasionally lupus inhibitors become increasingly evident with increasing dilution.[15] Unfortunately, the patient was discharged and the patient's specimen was not retained, and therefore we could not assess this for our case. Nevertheless, such an effect cannot be ruled out in our case, and instead of the suggestion of a low level of LA in our patient according to results of the dRVVT and SCT tests, should serial dilutions have been performed, a high titer LA may instead have been demonstrated.[15] This also validates the need to perform mixing and dilution studies on occasions for the identification of LA.[15]

Importantly, for our case, factor assays (II, V, VII, and X) performed by modified PT assays did not show any nonparallelism (unlike APTT-based factors). This is possibly due to the high concentration of phospholipid in PT reagents.[14] Such phospholipids bind with factor II to complex with, and be neutralized by, aPS/PT complex antibodies, leading to an increased clearance of the complexes in vivo instead of acting as an inhibitor in vitro. Unfortunately, PT prolongation correction tests, that is, a 1:1 mixture of patient plasma and normal plasma, were also not performed in this case.

A large number of studies have reported the correlation between aPS/PT complex antibodies and arteriovenous thrombosis, as well as adverse pregnancy, especially in patients with LA positivity.[12] [16] Presently, the average level of factor II in the reported cases of LAHPS is approximately 20%, mostly in systemic lupus erythematosus (SLE) and virus infection,[2] and the majority of patients do not show bleeding manifestations.[12] [16] The reason for LAHPS in this case was considered to be related to the EB virus infection. It has been proposed that a routine measurement of aPS/PT complex antibodies might be useful in establishing the thrombotic risk of patients with previous thrombosis and/or SLE.[12] [17] Such tests are expected to appear in future guidelines for the diagnosis of APS.[17] [18] For our case, clinicians were notified that the prolongation of APTT and PT appeared to be because of the interference of IgM aPS/PT complex antibody, but this finding did not suggest the presence of a coagulation bleeding disorder. On the contrary, attention should be paid to the potential risk (and prevention) of thrombosis in such patients. The patient was discharged from the hospital due to economic reasons and did not receive further treatment; thus, no follow-up was possible.

In summary, we describe a proposed case of LAHPS, in which significantly prolonged PT and APTT were evidenced in paradox to normal TEG results and lack of bleeding symptoms. After a series of laboratory examinations, we determined that the prolonged APTT and PT could be attributed to interference from the IgM aPS/PT complex antibody. As aPS/PT complex antibody testing may play an important role in the extended diagnosis of APS in patients previously identified as SNAPS, we recommended aPS/PT complex testing when a nonspecific intrinsic pathway factor inhibitor is evident and factor II activity is significantly low. In retrospect, we also advise of possible hook effects that may interfere with the testing of APTT, PT, dRVVT and SCT and that extended mixing studies are sometimes required in the detection of LA.

Author Contributions

All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

^* Joint first authors: These authors contributed equally to this work.

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