Antiphospholipid antibodies are persistently positive at high titers. Additive value of platelet-bound C4d

How to diagnose and manage antiphospholipid syndrome

Antiphospholipid antibodies (aPL) are autoimmune antibodies directed toward phospholipids or phospholipid-protein complexes, particularly those containing β2-glycoprotein I (β2GPI). Persistently positive aPL accompanied by arterial or venous thrombosis, or recurrent pregnancy loss, constitutes the antiphospholipid syndrome (APS). Several types of aPL with different specificities have been defined and may be detected in the clinical lab, including lupus anticoagulants (detected using clotting assays) and anticardiolipin, anti-β2GPI and anti-prothrombin/phosphatidylserine antibodies (detected by ELISA); each of the last 3 aPL may be either IgG, IgM, or IgA, though IgA antibodies are not included in criteria for APS. Due to the relative rarity of APS and the heterogeneity of aPL, thrombosis risk stratification is challenging, and randomized clinical trials for thrombosis treatment and prevention have been limited. This lack of high-quality data has made the clinical management of APS difficult, and existing guidelines are few and could not possibly cover many of the scenarios encountered in managing patients with APS. In this review, we present 3 patients with aPL and/or APS who highlight treatment dilemmas, and we discuss background information that may help guide clinical judgment in developing individualized treatment plans for patients with these enigmatic antibodies.

Complement biomarkers in the antiphospholipid syndrome - Approaches to quantification and implications for clinical management

Complement is a major driver of antiphospholipid syndrome (APS) and a promising therapeutic target in refractory and catastrophic APS. Complement testing in APS is largely limited to research settings, and reliable, rapid-turnaround biomarkers are needed to predict those at risk for adverse clinical outcomes and most likely to benefit from complement inhibition. We review complement biomarkers and their association with thrombosis and obstetric outcomes, including: (i) complement proteins and activation fragments in the fluid phase; (ii) assays that evaluate complement on cell membranes (e.g. in vivo cell-bound complement fragments, hemolytic assays, and ex vivo 'functional' cell-based assays, and (iii) sequencing of complement genes. Current studies highlight the inconsistencies in testing both between studies and various aPL/APS subgroups, suggesting that either cell-based testing or multiplex panels employing a combination of biomarkers simultaneously may be most clinically relevant. Standardization of complement assays is needed to ensure reproducibility and establish clinically relevant applications.

Role of Platelet-Bound C4d (PC4d) in Predicting Risk of Future Thrombotic Events in Systemic Lupus Erythematosus

OBJECTIVE

Platelet-bound complement activation product C4d (PC4d) levels correlate with history of thrombosis in patients with systemic lupus erythematosus (SLE). The present study evaluated whether PC4d levels could assess risk of future thrombosis events.

METHODS

PC4d level was measured by flow cytometry. Thromboses were confirmed by electronic medical record data review.

RESULTS

The study included 418 patients. Nineteen events (13 arterial and 6 venous) occurred in 15 subjects in the 3 years post-PC4d level measurement. PC4d levels above the optimum cutoff of 13 mean fluorescence intensity (MFI) predicted future arterial thrombosis with a hazard ratio of 4.34 (95% confidence interval [95% CI] 1.03-18.3) (P = 0.046) and a diagnostic odds ratio (OR) of 4.30 (95% CI 1.19-15.54). Negative predictive value of PC4d level of ≤13 MFI for arterial thrombosis was 99% (95% CI 97-100%). Although a PC4d level of >13 MFI did not reach statistical significance for prediction of total thrombosis (arterial and venous) (diagnostics OR 2.50 [95% CI 0.88-7.06]; P = 0.08), it was associated with all thrombosis (n = 70 historic and future arterial and venous events in the 5 years pre- to 3 years post-PC4d level measurement) with an OR of 2.45 (95% CI 1.37-4.32; P = 0.0016). In addition, the negative predictive value of PC4d level of ≤13 MFI for all future thrombosis events was 97% (95% CI 95-99%).

CONCLUSIONS

A PC4d level of >13 MFI predicted future arterial thrombosis and was associated with all thrombosis. Patients with SLE presenting with a PC4d level of ≤13 MFI had high probability of not experiencing arterial or any thrombosis in the 3 years afterwards. Taken together, these findings indicate that PC4d levels may help predict the risk of future thrombosis events in SLE.

Risk factors for persistent positive anticardiolipin antibodies in women with recurrent pregnancy loss

Antiphospholipid syndrome (APS) is an established cause of recurrent pregnancy loss (RPL). It is necessary to detect persistently positive antiphospholipid antibodies to diagnose APS. This study aimed to explore risk factors for persistent anticardiolipin (aCL) positivity. Women with a history of RPL or with a history of one or more intrauterine fetal deaths after 10 weeks underwent examinations to determine the causes of RPL, including antiphospholipid antibodies. If aCL-IgG or aCL-IgM antibodies were positive, retests were performed at least 12 weeks apart. Risk factors for persistent aCL antibody positivity were retrospectively investigated. The number and percentage of cases above the 99th percentile were 74/2399 (3.1%) for aCL-IgG, and 81/2399 (3.5%) for aCL-IgM. Of the initially tested cases, 2.3% (56/2399) for aCL-IgG and 2.0% (46/2289) for aCL-IgM were ultimately positive above the 99th percentile in retests. Retest values after 12 weeks were significantly lower than the initial values for both IgG and IgM immunoglobulin classes. Initial aCL antibody titers were significantly higher in the persistent-positive group than in the transient-positive group for both IgG and IgM immunoglobulin classes. The cut-off values for predicting persistent positivity of aCL-IgG antibodies and aCL-IgM antibodies were 15 U/mL (99.1 percentile) and 11 U/mL (99.2 percentile), respectively. The only risk factor for persistently positive aCL antibodies is a high antibody titer during the initial test. When the aCL antibody titer in the initial test exceeds the cut-off value, therapeutic strategies can be defined in subsequent pregnancies without waiting for 12 weeks.