**5.1 When to test?**

What raises the suspicion for APS in stroke? When should it be considered that more information and studies are needed besides the typical workup usually undertaken? The most pertinent situation would be when a younger patient (<50 years) presented with a thrombotic stroke without identified classic risk factors for ischemic/embolic stroke [71]. Initial workup may reveal exam and laboratory findings that may raise the concern for APS as listed in **Table 8**. Notably, subtle renal, cardiac, hematologic, and dermatologic system alterations can be indicative. Further, a family history of early-onset stroke, clotting, or other systemic features should be queried. Absence of typical risk factors including hypertension, diabetes, atrial fibrillation, or known history of coagulopathy (e.g. protein


#### **Table 8.**

*Other important clinical signs of APS not noted in Sapporo criteria, by body system. Adapted [63].*

### *Antiphospholipid Syndrome and Stroke DOI: http://dx.doi.org/10.5772/intechopen.101777*

C deficiency, protein S deficiency, antithrombin III), among others, further increases the consideration for APS. Notably, as many as 17% of cardiovascular events in those under 50 reveal aPL antibodies and up to 22% including anticardiolipin antibodies [54].

Of note, without suggestion of underlying coagulopathy or clinical findings (see **Table 8**) a young patient without classic risk factors, testing for many coagulopathies is not routinely performed. When performed, there is also the question of whether this workup needs to occur in the inpatient setting, during the patient's admission for stroke, or if it can be done post-discharge. When considering this, the most important question is: Will any findings acutely change management? It should also be noted that for a positive diagnosis APS testing needs to occur multiple times over a 3 month or longer time period. If considering the APS diagnosis, formal hematology and/or rheumatology consult is recommended. In general, the recommendation for inpatient vs. outpatient is that some workup may be deferred if necessary, to the outpatient setting, either under the care of the patient's primary physician/provider, neurologist, hematologist, or rheumatologist.

#### **5.2 What to test?**

Consistent with all stroke patients, every patient should receive standard stroke workup testing including brain imaging (CT brain, MRI brain), vessel imaging of the head, neck, and great vessels of the chest (CTA, MRA), cardiac imaging including a transthoracic echocardiogram (TTE) and laboratory testing (CMP, CBC, PT/ INR, aPTT, TSH, HgbA1C, lipid profile). A bubble study with the TTE should be considered if a paradoxical embolus from a DVT is on the differential. It is also recommended to obtain basic inflammatory markers such as sedimentation rate (ESR) and C-reactive protein (CRP) to evaluate for suggestion of diffuse inflammatory disease [24].

Transesophageal echocardiogram (TEE) should also be considered if the etiology remains uncertain, this is due to the increased frequency of valvular abnormalities in the setting of APS that may include irregular nodules/vegetations most commonly on the atrial side of the mitral valve or vascular side of the aortic valve, or if thickening of the valves is noted on TTE. Most commonly, the left side of the heart is the affected side with the mitral valve more commonly affected compared to the aortic valve. These cardiac changes are postulated to be due to immune complex damage and fibrosis [72].

If APS is being considered, it is recommended that while inpatient with the acute stroke the patient should have all antiphospholipid antibodies checked, according to the revised Sapporo laboratory criteria (see **Table 1**). Notably, this includes ELISA IgM/IgG for anticardiolipin (aCL) with a positive test showing medium to high titers (>40 GPL/MPL units or >99th percentile), which will need to be confirmed on at least two or more occasions, 12-weeks apart. Lupus anticoagulant (LA) should also be checked by two tests including dilute Russell viper venom time (dRVVT) and LA-sensitive PTT (PTT-LA)), again conformed on at least two occasions, 12-weeks apart. Lastly, an ELISA IgM/IgG for anti-beta2 glycoprotein I (β2GPI) should also be tested, with a positive value determined by titer in the 99th percentile, and again, should be tested on at least two occasions 12-weeks apart.

At least one clinical criterion (in the context of this chapter, most likely stroke) and one laboratory criterion should be met to diagnosis APS. As described, these tests are done 12-weeks apart, so the first set of lab tests will be performed inpatient and then the second 12-weeks later, typically performed in the outpatient setting.

As outlined in **Table 8**, if the patient does not meet revised Sapporo criteria, APS may still be diagnosed if clinical suspicion remains high based on multi-system abnormalities and if further etiologies are not identified [64].

If a patient inconsistently tests positive for APS, it may be warranted to also check for other autoimmune diseases, namely systemic lupus erythematosus (SLE), as up to 36% of those with APS will be positive for SLE. Having both APS and SLE increases the risk for stroke beyond having only one or the other [31].

#### **5.3 Understanding the tests**

As described above, there are 3 primary antibody tests for APS including aCL, LA, and β2GPI. Anticardiolipin (aCL) testing was first developed as a test for syphilis in the 1900s [71]. The aCL antibody was found not to be specific to just syphilis, thus its utility as a test for APS was also found after many false-positive syphilis tests showed an increased risk for thrombotic events. The tests presently use tissue derived from bovine tissue. Both IgG and IgM are evaluated by ELISA for the presence of aCL antibodies. Notably, due to cross-reactivity as discussed with syphilis, the presence of aCL does not alone confirm APS.

Lupus anticoagulant (LA) is a test for immunoglobulins that while associated with thrombosis, are associated with preventing coagulation in vivo. The process for testing LA is three tests including screening (usually with aPTT or dRVVT, clotting of phospholipid factors), mixing (correct with normal plasma), and confirmation (shortening prolongation with added phospholipid) [67]. Once again, LA by itself cannot confirm APS due to cross-reactivity. LA testing is outlined in **Figure 3**.

Anti-β2 glycoprotein I (β2GPI) enzyme-linked immunosorbent assay (ELISA) testing is the last of the trio of tests for APS. There are 5 main domains of the β2GPI,

**Figure 3.**

*Testing for lupus anticoagulant (Adapted [67]).*

### *Antiphospholipid Syndrome and Stroke DOI: http://dx.doi.org/10.5772/intechopen.101777*

labeled DI through DV. Anti-β2GPI largely targets domain I (DI). When this domain is targeted, it has been shown an association with thrombosis. The other domains DII through DV being targeted have not been shown to have as strong a connection for promoting thrombosis. Of note, there are some more rare entities that may also raise anti-β2GPI levels, such as leishmaniasis, leptospirosis, or leprosy. For APS, the associated antibodies are against the IgG form, whereas other elevates of anti-β2GPI may be directed towards the IgM variety [73].
