What this test measures
Anti-phospholipid antibody IgG (often anticardiolipin IgG by ELISA) — one of the laboratory criteria for antiphospholipid syndrome (APS). APS is an autoimmune disorder characterised by arterial / venous thrombosis and / or pregnancy morbidity (recurrent miscarriage, late fetal loss, severe preeclampsia, fetal growth restriction). Modern APS classification (Sydney + updated 2023 ACR/EULAR criteria) requires both clinical and laboratory criteria, with lab criteria persisting for at least 12 weeks.
Why it matters
APS is an important and treatable cause of unexplained thrombosis (DVT, stroke, MI in young), recurrent miscarriage, and severe pregnancy complications. Indian referral practice routinely includes APS workup in: (1) Young (< 50) patients with unprovoked VTE, especially recurrent. (2) Stroke or MI < 50 years without typical risk factors. (3) Recurrent pregnancy loss (≥ 3 first-trimester or ≥ 1 late). (4) Severe preeclampsia or HELLP before 34 weeks. (5) SLE patients (30-40% have APS antibodies). Treatment is anticoagulation (warfarin for venous, aspirin ± LMWH for obstetric).
How to prepare
No fasting required. Sample BEFORE starting anticoagulation if possible (heparin can interfere with lupus anticoagulant — though not with anticardiolipin IgG specifically). Disclose pregnancy, current illness (acute infections can transiently raise antibodies), and immunosuppressive therapy.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-Phospholipid IgG (GPL units (or U/mL))[1][2] | < 20 GPL (low); 20-40 (moderate); > 40 (high) | Negative or low (< 20 GPL): no APS by this criterion. | Moderate (20-40) or High (> 40) — APS classification requires HIGH titre AND persistence for at least 12 weeks. Single positive result does NOT diagnose APS. Confirm with: (1) repeat in 12 weeks; (2) IgM anticardiolipin; (3) anti-beta-2-glycoprotein-I; (4) lupus anticoagulant (LA — coagulation-based test). Triple positivity (LA + aCL + anti-β2GPI) carries highest thrombosis risk. |
APS antibody panel interpretation
| Pattern | Risk band | Implication |
|---|---|---|
| Single low-positive | Low | Repeat in 12 weeks; rule out transient |
| Single moderate-positive | Moderate | Repeat in 12 weeks; add other markers |
| Persistent single moderate-high | Moderate-High | Possible APS — clinical correlation |
| Double positive (any 2 markers) | High | APS likely if clinical criteria met |
| Triple positive (LA + aCL + β2GPI) | Very high | Highest thrombosis risk |
Frequently asked questions
Why is repeat testing in 12 weeks required?
Anti-phospholipid antibodies can be transiently positive after viral infections, vaccinations, drugs (e.g. some antibiotics) — these do NOT cause APS. Persistence at 12 weeks is what defines clinically meaningful APS antibodies.
What is the difference between IgG and IgM?
IgG anticardiolipin is more specific for APS and more strongly associated with thrombosis. IgM is more often transient and less specific. Both are tested but IgG carries more weight.
I have recurrent miscarriages — should I get this?
Yes — ≥ 3 first-trimester or ≥ 1 late (≥ 10 weeks) unexplained pregnancy losses warrant APS workup. Obstetric APS is treatable with LMWH + aspirin during pregnancy.
Is APS the same as lupus?
No, but they overlap. About 30-40% of SLE patients also have APS antibodies. APS can occur on its own (primary APS) or with SLE / other autoimmune disease (secondary APS).
How is APS treated?
Venous APS: lifelong warfarin (target INR 2-3, higher for arterial events or recurrence). Obstetric APS: low-dose aspirin from conception + therapeutic LMWH from positive pregnancy test until 6 weeks postpartum. DOACs (rivaroxaban, apixaban) are NOT recommended in triple-positive APS.
Will APS antibodies ever disappear?
Sometimes — especially low-titre transient positivity from infections. Persistent high-titre APS antibodies usually remain present for life.
Related Lipids / Cardiac Risk tests
Tests commonly ordered alongside ANTI PHOSPHOLIPID ANTIBODY (APL) - IGG, or that help interpret an unexpected result.
Sources & references
- Updated APS Criteria (2023 ACR/EULAR) · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Antiphospholipid Antibodies · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Antiphospholipid Syndrome · accessed 2026-05-30T00:00:00.000Z
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