Clinical Lab Diagnosis - Rheumatology Lecture - AI Generated Flash Cards

C-Reactive Protein (CRP)

Acute-phase protein made in the liver; sensitive but non-specific marker that rises ~6 h after tissue damage and falls as inflammation resolves (≈48 h half-life).

Erythrocyte Sedimentation Rate (ESR)

Indirect measure of inflammation; elevated fibrinogen makes RBCs stack and settle faster. Rises 24-48 h after injury and remains elevated 4-6 days.

Half-Life of CRP

Approximately 48 hours, making CRP useful for short-term (acute) inflammatory monitoring.

Half-Life of ESR

Roughly 4–6 days, so ESR is better for tracking longer-term (chronic) inflammation.

Highly Sensitive CRP (hs-CRP) Test

Assay that detects very low CRP levels; used to stratify cardiovascular (MI) risk.

Autoantibody

An antibody produced by the immune system that mistakenly targets the body’s own tissues.

Systemic Autoantibodies

Autoantibodies associated with multi-system diseases (e.g., ANA, ANCA, RF, anti-dsDNA, anti-Sm, CCP).

Organ-Specific Autoantibodies

Autoantibodies directed at antigens confined to one organ system (e.g., anti-tTG for gut, anti-TPO for thyroid).

Antinuclear Antibody (ANA)

Group of antibodies against nuclear components; positive in nearly all SLE patients but also other autoimmune and some healthy individuals.

Anti-Neutrophil Cytoplasmic Antibody (ANCA)

Autoantibody against cytoplasmic antigens in neutrophils; helps diagnose vasculitides.

Anti-Double-Stranded DNA (anti-dsDNA)

Highly specific (≈95 %) autoantibody for SLE; 70 % sensitivity.

Anti-Centromere Antibody (ACA)

Autoantibody associated with limited cutaneous systemic sclerosis (CREST syndrome).

Antihistone Antibody

Autoantibody commonly linked to drug-induced lupus.

Cyclic Citrullinated Peptide Antibody (CCP)

Autoantibody targeting citrullinated peptides; higher specificity and earlier detection for RA than RF.

Extractable Nuclear Antigen (ENA) Panel

Suite of autoantibody tests (e.g., anti-SS-A/Ro, anti-SS-B/La, anti-RNP, anti-Sm, Scl-70, anti-Jo-1) used after a positive ANA.

Rheumatoid Factor (RF)

IgM (or IgG/IgA) antibody against the Fc portion of IgG; positive in ~80 % of RA but not specific.

Cardiolipin Antibody

One of the antiphospholipid antibodies; associated with thrombosis and pregnancy loss.

Beta-2 Glycoprotein I Antibody

Antiphospholipid antibody targeting β2-GPI; part of APA profile.

Antiphospholipid Antibody (APA)

Family of autoantibodies (e.g., LA, anticardiolipin) causing a hypercoagulable state.

Lupus Anticoagulant (LA)

Antiphospholipid antibody that prolongs clotting times yet predisposes to thrombosis.

Islet Autoantibodies

Antibodies (e.g., GAD, IA-2) directed at pancreatic β-cells; indicate type 1 diabetes risk.

Insulin Antibody

Autoantibody against insulin; may appear in type 1 diabetes or after exogenous insulin exposure.

Anti-Tissue Transglutaminase (anti-tTG)

IgA autoantibody used as first-line serology for celiac disease.

Anti-Gliadin Antibody (AGA)

Older celiac serology; IgA/IgG against gliadin peptides.

Intrinsic Factor Antibody

Autoantibody causing pernicious anemia by blocking vitamin B12 absorption.

Parietal Cell Antibody

Autoantibody to gastric parietal cells; associated with autoimmune gastritis and pernicious anemia.

Thyroid Peroxidase Antibody (anti-TPO)

Key thyroid autoantibody; elevated in Hashimoto thyroiditis and Graves disease.

TSH Receptor Antibody / TSI

Stimulating antibody causing hyperthyroidism in Graves disease.

Smooth Muscle Antibody (SMA)

Autoantibody linked to autoimmune hepatitis type 1; F-actin specificity increases accuracy.

Antimitochondrial Antibody (AMA)

Marker for primary biliary cholangitis (AMA-M2 subtype most specific).

Liver Kidney Microsome-1 Antibody (anti-LKM-1)

Autoantibody characteristic of autoimmune hepatitis type 2.

Anti-Glomerular Basement Membrane (GBM) Antibody

Autoantibody causing Goodpasture syndrome with renal and pulmonary involvement.

Acetylcholine Receptor (AChR) Antibody

Autoantibody against neuromuscular junction receptors; diagnostic for myasthenia gravis.

2010 ACR/EULAR RA Classification

Point-based system (joint count, serology, duration, acute-phase reactants); ≥6 points = rheumatoid arthritis.

Anti-CCP vs. RF

Combining both raises sensitivity for RA; anti-CCP adds higher specificity and earlier detection.

HLA-B27 Antigen

Genetic marker present in ~6 % population; 80-90 % of ankylosing spondylitis patients are positive.

Ankylosing Spondylitis (AS)

Seronegative spondyloarthropathy characterized by sacroiliitis and spine fusion; strongly linked to HLA-B27.

Seronegative Spondyloarthropathies

Group of RF-negative arthritides (AS, psoriatic, reactive arthritis, IBD-associated) sharing axial involvement and HLA-B27 association.

IgA Tissue Transglutaminase (tTG) with Total IgA

First-step algorithm to screen for celiac disease; IgA deficiency necessitates alternate IgG tests.

IgG Deaminated Gliadin Peptide (DGP)

Second-line celiac test used when IgA deficient or tTG negative but suspicion remains.

SLICC Criteria for SLE

Requires ≥4 criteria (≥1 clinical & ≥1 immunologic) or lupus nephritis with positive ANA/anti-DNA.