What each antibody points to, what it is worth, and what it obliges you to do next. The action column is the part that matters: an antibody that does not change management is a laboratory result, not a clinical finding.
| Antibody | Points to | Diagnostic worth | Action it obliges |
|---|---|---|---|
| Anti-dsDNA | SLE, lupus nephritis | 6 points in the 2019 criteria, but only on an assay with 90 per cent or better specificity. A screening ELISA does not qualify. | Monitor serially. A rising titre with falling C3 and C4 precedes a nephritis flare. |
| Anti-Sm | SLE, essentially only SLE | The most specific antibody in the panel. Specificity 99.7 per cent, likelihood ratio around 65, but sensitivity only 17 per cent. | Establishes the diagnosis. Do not repeat it: it does not track activity. |
| Anti-nucleosome | SLE | Similar specificity to anti-Sm with more than twice the sensitivity, around 42 per cent. Under-used in Indian laboratories. | Worth requesting when SLE is suspected and dsDNA and Sm are negative. |
| Anti-ribosomal P | Neuropsychiatric SLE, lupus hepatitis | Specificity around 99.6 per cent, sensitivity around 32 per cent. | In a patient with psychosis, supports a lupus attribution. It does not remove the obligation to exclude CNS infection first. |
| Anti-histone | Drug-induced lupus, but also idiopathic SLE | Sensitive, not specific. Useless without the drug history. | Take a full drug history including isoniazid, hydralazine, phenytoin, minocycline and anti-TNF agents. |
| Anti-U1 RNP | MCTD at high titre, SLE at any titre | High titre with no SLE-specific antibody suggests MCTD, but clinical features are still required. | Baseline echocardiography. Pulmonary arterial hypertension is the leading cause of death in MCTD. |
| Anti-DFS70 | Argues against a rheumatic disease | Only when monospecific, that is with no other antibody detectable. Present in a few per cent of healthy people. | In an otherwise well person with a dense fine speckled ANA, this is the result that lets you stop. |
| Antibody | Points to | Diagnostic worth | Action it obliges |
|---|---|---|---|
| Anti-Ro60 (SSA) | Sjögren's, SLE, subacute cutaneous lupus | 3 of the 4 points needed to classify Sjögren's. Cannot classify alone. | In a woman planning or carrying a pregnancy, this is the finding that changes obstetric care. |
| Anti-Ro52 (TRIM21) | Myositis, antisynthetase syndrome, interstitial lung disease, autoimmune hepatitis | Frequently misreported as a Sjögren's marker. It is not one in isolation. | Where the phenotype includes lung disease, treat as a signal to screen the lungs. |
| Anti-La (SSB) | Sjögren's, when accompanying anti-Ro | Absent from the 2016 criteria. An isolated anti-La carries little weight. | Do not diagnose Sjögren's on an isolated anti-La. |
| Antibody | Phenotype | Principal organ risk | Action it obliges |
|---|---|---|---|
| Anti-topoisomerase I (Scl-70) | Diffuse cutaneous systemic sclerosis | Interstitial lung disease | Baseline HRCT thorax and pulmonary function tests, then serial monitoring. |
| Anticentromere | Limited cutaneous disease, the CREST phenotype | Pulmonary arterial hypertension, late | Annual echocardiography. Lung fibrosis is less likely. |
| Anti-RNA polymerase III | Rapidly progressive diffuse skin thickening | Scleroderma renal crisis; also an association with malignancy around disease onset | Daily home blood pressure monitoring, and age-appropriate cancer screening. |
| Anti-PM-Scl | Sclerosis and myositis overlap | Lung and muscle | Assess both compartments. |
| Anti-fibrillarin (U3 RNP) | Diffuse disease, often younger patients | Pulmonary hypertension, cardiac and renal | Echocardiography and cardiac assessment. |
| Anti-Th/To | Limited disease | Interstitial lung disease and pulmonary hypertension | Do not be reassured by limited skin involvement. Screen the lungs. |
| Antibody | Syndrome | What it predicts | Action it obliges |
|---|---|---|---|
| Anti-Jo-1 and other antisynthetases | Antisynthetase syndrome: myositis, ILD, arthritis, mechanic's hands, Raynaud's, fever | Interstitial lung disease dominates the prognosis, and can precede the muscle disease | HRCT thorax and pulmonary function tests at diagnosis, whatever the CK. |
| Anti-MDA5 | Clinically amyopathic dermatomyositis with rapidly progressive ILD; cutaneous ulceration and palmar papules | Rapidly progressive, frequently fatal interstitial lung disease. CK is often normal or near normal, which is the point that catches people out | Urgent HRCT thorax. Early aggressive combined immunosuppression. Treat as a respiratory emergency, not a dermatological finding. |
| Anti-TIF1-gamma | Adult dermatomyositis with prominent skin disease | The strongest malignancy association among the myositis antibodies in adults. In juvenile disease it carries no malignancy association | Age-appropriate and symptom-directed malignancy screening at diagnosis, and repeated over the following three years. |
| Anti-NXP2 | Dermatomyositis with calcinosis | Calcinosis, severe muscle disease; malignancy association in adults | Malignancy screening in adults. Anticipate calcinosis in juvenile disease. |
| Anti-Mi-2 | Classic dermatomyositis with the full rash | Good response to treatment, favourable prognosis, low malignancy risk | Reassure, and treat conventionally. |
| Anti-SAE | Dermatomyositis, skin often precedes muscle | Dysphagia is common | Assess swallowing. |
| Anti-SRP | Immune-mediated necrotising myopathy | Very high CK, severe weakness, poor response to corticosteroids alone; cardiac involvement described | Early escalation beyond steroids: intravenous immunoglobulin or rituximab. |
| Anti-HMGCR | Immune-mediated necrotising myopathy, statin-associated | Weakness that persists or progresses after the statin is stopped. Can also occur without any statin exposure | Stop the statin, but do not expect that to be enough. Immunosuppression, often with intravenous immunoglobulin, is usually required. |
| Anti-Ku | Myositis and sclerosis overlap | Variable, often overlap features | Assess for both. |
| Result | Points to | Cautions | Action it obliges |
|---|---|---|---|
| PR3-ANCA | Granulomatosis with polyangiitis | Also positive in cocaine adulterated with levamisole, which produces a strikingly similar destructive nasal picture | Ask about cocaine use before accepting the diagnosis. Exclude tuberculosis before accepting a cavitating lung lesion as GPA. |
| MPO-ANCA | Microscopic polyangiitis, EGPA, drug-induced vasculitis | The least specific result in the panel. Also seen in inflammatory bowel disease, autoimmune hepatitis, primary sclerosing cholangitis, endocarditis and tuberculosis, and with propylthiouracil, hydralazine and minocycline | A positive MPO-ANCA without a vasculitic syndrome is not a diagnosis and is not an indication to treat. |
| Immunofluorescence pattern alone | Nothing definite | The 2017 international consensus moved to antigen-specific immunoassay for PR3 and MPO as the primary screen. A c-ANCA or p-ANCA report without antigen specificity is an incomplete result | Request the antigen-specific assay before acting. |
| Anti-GBM | Anti-glomerular basement membrane disease | Around a third are also ANCA positive, usually MPO. Double-positive disease behaves like anti-GBM acutely and like ANCA vasculitis in its tendency to relapse | A true emergency. Plasma exchange, corticosteroids and cyclophosphamide, without waiting for biopsy where the presentation is fulminant. Test for ANCA in every anti-GBM patient. |
| Assay | Note | Action it obliges |
|---|---|---|
| Lupus anticoagulant | The strongest single predictor of thrombosis of the three. Cannot be interpreted reliably on warfarin, a direct oral anticoagulant, or during acute thrombosis | Time the test. If the patient is anticoagulated, say so on the request form and interpret with the laboratory. |
| Anticardiolipin IgG or IgM | Only medium or high titre counts: above 40 GPL or MPL units, or above the 99th centile | A low-titre transient positive after infection is common and should not be classified. |
| Anti-beta-2 glycoprotein I | Above the 99th centile | Part of the triple-positive assessment. |
| Triple positivity | All three positive carries the highest thrombotic risk | Warfarin, not a direct oral anticoagulant. The TRAPS trial found rivaroxaban inferior to warfarin in triple-positive patients, with excess arterial events. |
A module organised around antibodies can imply, by its silence, that a negative panel is reassuring. It is not. The following are substantially or entirely seronegative, and several are more common in Indian practice than the diseases above.
| Disease | How it is diagnosed instead |
|---|---|
| Takayasu arteritis | Imaging of the aorta and its branches: CT or MR angiography. Young Indian women with limb claudication, absent pulses, a blood pressure difference between arms, or unexplained hypertension. No serological marker. |
| Behçet's disease | Clinical: recurrent oral and genital ulceration, uveitis, pathergy. HLA-B51 supports but does not diagnose. |
| Axial spondyloarthritis | Inflammatory back pain, sacroiliac imaging, HLA-B27. ANA and RF are irrelevant. |
| Adult-onset Still's disease | Quotidian fever, evanescent rash, arthritis, very high ferritin with a low glycosylated fraction. Diagnosis of exclusion. ANA and RF negative by definition in the classification criteria. |
| Sarcoidosis | Histology showing non-caseating granulomas, after tuberculosis has been excluded. In India that exclusion is the whole difficulty. |
| IgG4-related disease | Histology with storiform fibrosis and IgG4-positive plasma cells. Serum IgG4 is neither sensitive nor specific enough to stand alone. |
| Polymyalgia rheumatica and giant cell arteritis | Clinical, with acute phase response, temporal artery imaging or biopsy. |
| ANA-negative SLE | A small but real group. The 2019 criteria cannot classify them, and the authors say so explicitly. Classification criteria are not diagnostic criteria. |
What it is. The probability that the patient has the disease before the test result is known, estimated from the clinical presentation.
Why it matters. In the United States NHANES survey, antinuclear antibodies were present in 13.8 per cent of the population aged 12 and over. Take a hypothetical clinic where 1,000 people are tested and 20 of them have lupus. If the ANA has a sensitivity of 98 per cent and a specificity of 90 per cent, about 20 of the 20 with lupus test positive and about 98 of the 980 without it also test positive. Of 118 positive results, 20 are true. A positive ANA in that setting is wrong about five times out of six. Nothing about the assay changed; only the prior did.
Bedside pearl. The question to ask before ordering an ANA is not "could this be lupus" but "what would I do differently if it came back positive, and what would I do differently if it came back negative". If the answer to both is "nothing", the test is not indicated. Ordering an ANA to reassure a patient with fatigue reliably achieves the opposite.
Indian context. ANA is increasingly ordered from primary care and by direct-to-consumer laboratory packages, often as part of a bundled panel the patient bought without a clinical question attached. A great deal of rheumatology outpatient time in Indian teaching hospitals is now spent unpicking an incidental low-titre ANA in a well person. This module's stage 1 exists to make that prior explicit before the number is looked at.
| The mimic | How it presents | Which antibodies it can turn positive | What separates them |
|---|---|---|---|
| Tuberculosis | Chronic fever, weight loss, cavitating lung lesions resembling GPA, serositis, Poncet's reactive polyarthritis | RF, low-titre ANA, occasionally ANCA | Tissue diagnosis, CBNAAT, culture. A cavitating lesion in India is tuberculosis until proven otherwise. |
| Leprosy | Polyarthritis, neuropathy, skin lesions. Type 2 lepra reaction with erythema nodosum leprosum closely mimics systemic vasculitis | ANA, RF, sometimes ANCA, and false-positive antiphospholipid antibodies | Slit skin smear, nerve thickening, the distribution of the skin lesions. |
| Dengue and chikungunya | Severe symmetric polyarthritis, rash, thrombocytopenia. Chikungunya arthritis can persist for months and is regularly mistaken for early rheumatoid arthritis | RF, low-titre ANA, transient antiphospholipid antibodies | The epidemic context, the acute febrile prodrome, and serology for the virus. |
| Kikuchi-Fujimoto disease | Young woman, fever, tender cervical lymphadenopathy, cytopenias. Reproduces an SLE flare closely, and can coexist with SLE | Low-titre ANA | Lymph node biopsy. There is no serological shortcut. |
| HIV | Cytopenias, arthralgia, sicca, vasculitic rash, diffuse infiltrative lymphocytosis syndrome resembling Sjögren's | ANA, RF, antiphospholipid antibodies | HIV testing before immunosuppression, without exception. |
| Hepatitis C | Cryoglobulinaemic vasculitis, arthralgia, sicca | RF strongly positive, ANA, antiphospholipid antibodies | Hepatitis C serology and viral load. It is also a formal exclusion in the Sjögren's criteria. |
| Infective endocarditis | Fever, glomerulonephritis, splinter haemorrhages, low complement, cytopenias. Reproduces lupus nephritis and ANCA vasculitis together | ANCA, RF, ANA, low C3 and C4 | Blood cultures before antibiotics, and echocardiography. This is the classic error: a patient given pulse steroids for a presumed pulmonary-renal syndrome who had endocarditis. |
| IgG4-related disease | Tumefactive masses, pancreatitis, sialadenitis, retroperitoneal fibrosis. Mimics Sjögren's and vasculitis | Modestly raised serum IgG4; ANA can be positive | Histology showing storiform fibrosis and an IgG4-positive plasma cell infiltrate. |
Why it matters. Repeating a static marker costs money, delays nothing and answers no question. In a system where the patient is often paying out of pocket, a repeated ENA panel is a real harm.
What it is. The staining pattern on HEp-2 cells, now standardised internationally as ICAP anti-cell (AC) codes.
Why it matters. The pattern predicts which antibodies will be found and, occasionally, tells you to stop looking. A titre reported without a pattern has discarded half of what the test produced.
| Pattern | ICAP code | Expect | Associations |
|---|---|---|---|
| Homogeneous | AC-1 | dsDNA, nucleosome, histone | SLE, drug-induced lupus, juvenile idiopathic arthritis |
| Dense fine speckled | AC-2 | DFS70, and nothing else | Argues against a rheumatic disease when monospecific |
| Centromere | AC-3 | CENP-A, CENP-B | Limited cutaneous systemic sclerosis, primary biliary cholangitis |
| Fine or coarse speckled | AC-4, AC-5 | Ro, La, Sm, U1 RNP | SLE, Sjögren's, MCTD |
| Nuclear dots | AC-6, AC-7 | Sp100, PML | Primary biliary cholangitis |
| Nucleolar | AC-8 to AC-10 | Scl-70, PM-Scl, fibrillarin, Th/To, RNA pol I | Systemic sclerosis and overlap |
| Nuclear envelope | AC-11, AC-12 | gp210, lamins | Primary biliary cholangitis, autoimmune hepatitis |
| Cytoplasmic | AC-15 to AC-21 | Jo-1, ribosomal P, AMA-M2, SRP | Myositis, neuropsychiatric SLE, primary biliary cholangitis |
Bedside pearl. A cytoplasmic pattern is frequently reported by laboratories as "ANA negative", because strictly it is not nuclear. In a patient with myositis or unexplained interstitial lung disease that reported negative may be concealing an anti-Jo-1. Read the comment on the report, not only the conclusion.
What it is. Classification criteria exist to assemble homogeneous groups for research. They are deliberately weighted towards specificity so that trial cohorts are clean.
Why it matters. The authors of the 2019 SLE criteria state directly that the criteria "should never be used to exclude patients who do not fully meet these criteria from receiving appropriate therapies". A patient scoring 8 who is clinically obvious still has lupus and still needs treating. This module reports the score and says whether the threshold is met; it does not tell you whether to treat.
Bedside pearl. The commonest misuse is the reverse of the one people expect. It is not that criteria are used too loosely; it is that a patient who genuinely has the disease is denied treatment because a score came to 8 rather than 10.
What it is. A likelihood ratio converts a pre-test probability into a post-test probability. Post-test odds equal pre-test odds multiplied by the likelihood ratio.
Why it matters. Sequential multiplication of likelihood ratios is only valid when the tests are conditionally independent given the disease state. Autoantibodies are strongly correlated: a patient with anti-Sm is far more likely than chance to also have anti-dsDNA and a high-titre ANA. Multiplying them treats correlated evidence as though it were independent, and the resulting probability can be badly overstated.
What this module does instead. It applies the single strongest likelihood ratio present, names it, and states its source and its limitations on screen. The one composite figure it does use, the likelihood ratio attached to the number of positive autoantibodies, was measured as a composite in the source study and is therefore legitimate to use as a single step.
Provenance of the numbers. The likelihood ratios come from Lin and colleagues, a retrospective study of 1,297 patients tested at a single Chinese tertiary hospital, of whom 148 had SLE. The comparison group is other patients who had the panel sent, not healthy people, so these figures describe a rheumatology referral population. They should not be applied to unselected screening, and no equivalent Indian dataset was available to me. Where the module shows a probability it repeats this caveat.
Stated so that the boundary is explicit rather than implied.
AMA Style:
Umakanth S. ANA & Autoimmune Serology Pathway. MEDiscuss. Published 2026. Accessed .
Vancouver Style:
Umakanth S. ANA & Autoimmune Serology Pathway [Internet]. MEDiscuss.org; 2026 [cited ]. Available from:
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