Antiphospholipid syndrome is a thrombo-inflammatory autoimmune disorder with a complex antiphospholipid antibody-mediated pathogenesis, and high heterogeneity in clinical presentation and disease course. Clinical presentation in antiphospholipid syndrome includes venous and arterial thrombosis, pregnancy complications, and a broad range of microvascular and non-thrombotic manifestations

APS may manifest as a primary, isolated condition or as a secondary disorder in conjunction with other autoimmune diseases, notably systemic lupus erythematosus (SLE) . The syndrome presents in two primary forms: thrombotic APS, marked by blood clots in both venous and arterial vessels, and obstetric APS (OAPS). While the criteria for APS diagnosis emphasize specific clinical and laboratory findings, recent research highlights the variability in antibody profiles and the potential for seronegative APS cases, complicating both diagnosis and management. Of note, thrombocytopenia is likely associated with more severe disease, and prolonged mild to moderate thrombocytopenia is linked to decreased long-term survival.

The neutrophil-lymphocyte ratio (NLR), defined as the ratio of the absolute value of neutrophils and lymphocytes in a peripheral venous blood stream, has been previously described as a non-invasive marker of the balance between the innate and adaptive immune response: neutrophils and lymphocytes are indeed indicators, respectively, of an active inflammatory state and of the regulatory pathway's activity in the immune system. Prior studies demonstrated that NLR is an easily available, cheap and widespread biomarker of systemic inflammation as well as a valid prognostic marker in multiple conditions, including cardiovascular, infectious, and chronic inflammatory diseases.

Alongside NLR, the platelet-to-lymphocyte ratio (PLR) has recently gained attention as a simple, cost-effective, and dependable marker that reflects inflammation, atherosclerosis, and cellular immune activation. An increased NLR, which represents the interaction between innate immunity driven mainly by neutrophils and adaptive immunity mediated by lymphocytes, and elevated PLR, as an indicator of inflammation and immune response, have been linked to acute thrombotic complications and are predictive of mortality in patients with solid tumors. However, their comparative evaluation between primary and secondary antiphospholipid syndrome (APS) remains limited.

Given the significant roles of inflammation, neutrophils, and platelets in the pathogenesis of venous thromboembolism (VTE), there has been growing interest in these parameters. NLR and PLR, both derived easily from complete blood counts, reflect primary hemostasis and inflammatory status. These ratios are minimally influenced by factors such as age, sex, and various physiological or pathological conditions, thereby potentially offering greater accuracy in detecting deep vein thrombosis (DVT) compared to other blood-based indices.

It is also noted that larger platelets are metabolically more active compared to smaller ones, producing higher quantities of β-thromboglobulin and thromboxane A2, substances associated with enhanced platelet activity, including increased expression of adhesion molecules and heightened aggregation ability.

NLR serves as an effective measure of systemic inflammation by reflecting the relative levels of neutrophils and lymphocytes. Substantial evidence now supports elevated NLR as a potential diagnostic and prognostic marker in a variety of cardiovascular and cerebrovascular diseases.

Similarly, PLR has been demonstrated to reliably reflect systemic inflammatory responses and is useful in predicting prognosis and outcomes in various conditions.

Mean platelet volume (MPV), which measures the average size of platelets in the blood, serves as an important parameter reflecting platelet function and activation, playing a key role in both inflammation and atherosclerosis.

Inclusion Criteria:

• Adults (age ≥18 years)
• Diagnosis of APS based on updated Sydney classification criteria confirmed by: Clinical history of thrombosis and/or pregnancy morbidity, Persistent presence (≥12 weeks) of antiphospholipid antibodies (aCL, anti-β2-glycoprotein I, and/or lupus anticoagulant)

Exclusion criteria:

• Current infection or inflammatory condition unrelated to APS
• Hematological malignancies or other blood disorders
• Recent blood transfusion or platelet-altering medications other than APS treatments

Patients will be categorized as:

Primary APS: APS without other systemic autoimmune diseases Secondary APS: APS associated with autoimmune diseases such as systemic lupus erythematosus (SLE)