Antiphospholipid antibodies (aPLs) are autoantibodies that bind to phospholipid-associated proteins that are located in many types of cells, such as the walls of blood vessels, as well as in the cells of the endometrial mucosa and in the cells derived from embryonic development (trophoblast). When they bind to the target cell, they can perform several functions, such as activating coagulation in the case of the vascular walls, or even changing the functioning program of a cell, such as in the endometrium or decidua.
A positive result for these autoantibodies does not translate into an immediate risk of suffering an episode related to coagulation activation (thrombosis). Similarly, a negative result should be carefully evaluated when the suspicion of the presence of antiphospholipid antibodies is high. In these cases, I recommend repeating the determination in a different laboratory. This is because the detection techniques are not well standardized and not all diagnostic kits are able to detect the antibodies of all patients. Similarly, professionals should be familiar with the different performance of each of the measurement techniques for these antibodies, since the results are not directly equivalent nor can the same threshold be established from which to consider the values as positive.
There are many antiphospholipid antibodies:
- The «classic» anti-cardiolipin and anti-beta-2-glycoprotein-I (anti-B2GPI) that are usually determined are IgG and IgM.
- However, there are other antiphospholipid antibodies called «non-classic» because they were described or their usefulness was seen later and which include anti-B2GPI of type IgA, anti-phosphatidylserine/prothrombin, anti-annexin II, anti-annexin V, anti-phosphatidylcholine, anti-phosphatidylserine, anti-phosphatidylethanolamine, etc.
In our data we found the presence of these antibodies in up to 29% of reproductive medicine patients around 20-25% patients with recurrent implantation failure and early recurrent miscarriages.
Antiphospholipid antibodies can be related in some patients to an increase in NK cells in the blood. This association has been observed in multiple studies and has been related to an earlier onset of obstetric events.
The first determinations to be performed are:
- Lupus anticoagulant: it is a factor, possibly a mixture of autoantibodies and blood proteins, which, contrary to what its name suggests, exerts a procoagulant activity. The problem with its name comes from the fact that in the blood extracted (ex-vivo), it produces antagonistic effects to those it produces in the body (in-vivo). Thus, it is able to prolong clotting times. Its persistent presence over time is usually associated with thrombotic phenomena. There are two methods for its determination, both complementary, the dRVVT, or snake venom derivative, indicating its name the origin of the reagents that are used to demonstrate it, and the technique based on Silica (Silica Clotting Time or SCT). Many colleagues in the field of Antiphospholipid Vascular Syndrome have related it to the presence of anti-phosphatidylserine/prothrombin antibodies, especially IgM.
- Anti-cardiolipin IgG
- Anti-cardiolipin IgM
- Anti-beta-2-glycoprotein-I (B2GPI) IgG
- Anti-beta-2-glycoprotein-I (B2GPI) IgM
These four antiphospholipid antibodies can be determined by different techniques or methodologies. The correlation between these techniques is far from acceptable, so a positive result by one methodology may be negative by another. This occurs especially in cases where the amount or concentration of the antibodies detected is low or is surrounding the cut-off point.
If the suspicion of their presence is high, my recommendation will be to repeat the determination by another different technique and if they are positive for one of them, to keep the following tests in the laboratory in which they have been positive. The most common detection techniques are:
- ALBIA methodology: it is a technique based on magnetic beads
- Enzyme immunoassay (EIA) methodology: it is a solid-phase determination technique
- ELISA methodology: it is the classic test with which these autoantibodies were described
- Chemiluminescence (CLIA) methodology: it is another technique based on magnetic beads.
If the previous ones were negative and there was a suspicion of the presence of antiphospholipid antibodies, it would be necessary to study:
- Anti-beta-2-glycoprotein-I (B2GPI) IgA
- Anti-phosphatidylserineprothrombin (PS/PT) IgG
- Anti-phosphatidylserineprothrombin (PS/PT) IgM
- Anti-annexin V IgG
- Anti-annexin V IgM