Diagnostic Tests

1. Overview: What this test reveals and why it is important Thyrotropin receptor antibodies (TRAb) are autoantibodies directed against the thyroid‑stimulating hormone receptor (TSHR) located on thyroid follicular cells. These antibodies are the hallmark of Graves’ disease, the most common cause of hyperthyroidism. TRAb testing detects three functional types of antibodies: · Thyroid‑stimulating antibodies (TSAb): Bind to and activate the TSHR, mimicking TSH, causing unregulate

1. Overview: What this test reveals and why it is important Anti‑CCP antibodies are autoantibodies directed against peptides containing the amino acid citrulline. Citrullination is a post‑translational modification of arginine residues, a process that becomes dysregulated in the inflamed synovium of patients with rheumatoid arthritis (RA). These antibodies target citrullinated proteins (e.g., fibrinogen, vimentin, enolase) and are produced by plasma cells in the joint and lym

1. Overview: What this test reveals and why it is important Anti‑Saccharomyces cerevisiae antibodies (ASCA) are autoantibodies directed against oligomannosidic epitopes of the cell wall of the yeast Saccharomyces cerevisiae (baker’s yeast). They are predominantly of the IgG and IgA isotypes. ASCA are serological markers of altered immune response to commensal microorganisms, reflecting loss of tolerance to fungal antigens in genetically susceptible individuals. Clinical utili

1. Overview: What this test reveals and why it is important p‑ANCA (perinuclear anti‑neutrophil cytoplasmic antibody) is an autoantibody directed against antigens within the cytoplasm of neutrophils. When detected by indirect immunofluorescence on ethanol‑fixed neutrophils, p‑ANCA produces a characteristic perinuclear staining pattern. The primary target antigen for true p‑ANCA is myeloperoxidase (MPO) , though other antigens (elastase, lactoferrin, cathepsin G, etc.) can pro

1. Overview: What this test reveals and why it is important HLA‑B27 is not a typical blood test that measures a concentration or enzyme activity. It is a genetic marker – specifically, a human leukocyte antigen (HLA) class I surface protein encoded by the HLA‑B locus on chromosome 6. The test detects the presence or absence of the HLA‑B27 allele. This allele is strongly associated with a group of inflammatory rheumatic diseases known as spondyloarthropathies. The most importa

1. Overview: What this test reveals and why it is important Thyroid peroxidase (TPO) is a key enzyme located in the thyroid follicular cells. It catalyses the iodination of tyrosine residues on thyroglobulin and the coupling of iodotyrosines to form thyroid hormones (T3 and T4). TPO antibodies (TPOAb) are autoantibodies directed against this enzyme, primarily of the IgG class. The presence of TPOAb indicates autoimmune thyroid disease (AITD) , the most common organ‑specific a

1. Overview: What this test reveals and why it is important Rheumatoid factor (RF) is an autoantibody directed against the Fc portion of immunoglobulin G (IgG) . It is typically of the IgM isotype, though IgG and IgA isotypes also exist. RF is produced by plasma cells in the synovium and lymphoid tissue and forms immune complexes with IgG, contributing to the inflammatory cascade in rheumatoid arthritis (RA) and other systemic autoimmune diseases. Clinical utility: · Diagnosi

1. Overview: What this test reveals and why it is important The antinuclear antibody (ANA) test detects autoantibodies directed against components of the cell nucleus. These antibodies target DNA, histones, ribonucleoproteins, and other nuclear antigens. A positive ANA indicates that the immune system has lost tolerance to self‑nuclear material and is producing antibodies that may attack the body's own tissues. This test is the primary screening tool for systemic autoimmune r

1. Overview: What this test reveals and why it is important Folate receptor antibodies (FRA) are autoantibodies directed against the folate receptor alpha (FRα) , a membrane-bound protein responsible for transporting folate across cell membranes, particularly into the brain via the choroid plexus. This test detects the presence of immunoglobulin G (IgG) and sometimes immunoglobulin A (IgA) antibodies that bind to the folate receptor and block its function. The clinical signif

1. Overview: What this panel reveals and why it is important Iron studies are not a single measurement but a physiological inventory of body iron supply, transport, and storage. Unlike a complete blood count which quantifies red cell mass, iron studies interrogate the metabolic pathway of iron—from dietary absorption and plasma transport to cellular utilisation and storage reserves. The panel answers four distinct questions: · Is there iron deficiency? (Low ferritin, low tran

1. Overview: What this test reveals and why it is important The Systemic Inflammation Response Index (SIRI) is a novel, integrated inflammatory biomarker derived from the complete blood count with differential. It is calculated as: SIRI = (Neutrophil count × Monocyte count) ÷ Lymphocyte count SIRI uniquely captures the interplay between three key myeloid and lymphoid lineages: · Neutrophils – first‑line innate immune effectors, drivers of acute and chronic inflammation, media

1. Overview: What this test reveals and why it is important The Systemic Immune‑Inflammation Index (SII) is a novel, integrated inflammatory biomarker derived from the complete blood count. It is calculated as: SII = (Platelet count × Neutrophil count) ÷ Lymphocyte count SII uniquely captures the balance between three distinct immune‑haematopoietic lineages: · Platelets – mediators of thrombosis, endothelial activation, and inflammation. · Neutrophils – first‑line innate immu

1. Overview: What this test reveals and why it is important The platelet–lymphocyte ratio (PLR) is a simple, inexpensive, and widely available inflammatory marker derived from the complete blood count with differential. It is calculated by dividing the absolute platelet count by the absolute lymphocyte count. PLR reflects the interplay between two distinct haematopoietic lineages: · Platelets are anucleate cell fragments derived from megakaryocytes. Beyond their canonical rol

1. Overview: What this test reveals and why it is important The neutrophil–lymphocyte ratio (NLR) is a simple, inexpensive, and widely available inflammatory marker derived from the complete blood count with differential. It is calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. NLR reflects the dynamic balance between two key arms of the immune system: · Neutrophils are the frontline responders of the innate immune system. They phagocytose

1. Overview: What this test reveals and why it is important The lymphocyte–monocyte ratio (LMR) is a simple, inexpensive inflammatory marker derived from the complete blood count with differential. It is calculated by dividing the absolute lymphocyte count by the absolute monocyte count. LMR reflects the balance between two key white blood cell lineages: · Lymphocytes are the orchestrators of adaptive immunity – they include T cells, B cells, and natural killer cells. They de

1. Overview: What this test reveals and why it is important Total cholesterol measures the sum of all cholesterol carried in the blood – primarily within low‑density lipoprotein (LDL), high‑density lipoprotein (HDL), and very‑low‑density lipoprotein (VLDL) particles. It is the most frequently ordered lipid test and serves as the initial screening tool for assessing cardiovascular risk. Cholesterol is an essential molecule – it stabilises cell membranes, serves as a precursor

1. Overview: What these tests reveal and why they are important Dengue is a mosquito-borne viral infection caused by four distinct serotypes (DENV-1 to DENV-4). It is endemic in tropical and subtropical regions, including the Indian subcontinent, Southeast Asia, and Latin America. The clinical presentation ranges from asymptomatic or mild febrile illness to severe dengue (dengue haemorrhagic fever/dengue shock syndrome), characterised by plasma leakage, bleeding, and organ im

1. Overview: What this test reveals and why it is important Very low‑density lipoprotein (VLDL) is one of the three major classes of lipoproteins, along with LDL and HDL. It is synthesised by the liver and serves as the primary carrier of endogenous triglycerides – triglycerides produced in the liver, as opposed to those absorbed from the diet. VLDL particles are larger and less dense than LDL, and as they circulate, they undergo lipolysis, losing triglycerides and becoming s

1. Overview: What this test reveals and why it is important The LDL / HDL ratio is calculated by dividing low‑density lipoprotein cholesterol (LDL‑C) by high‑density lipoprotein cholesterol (HDL‑C). It was historically promoted as a single number capturing both pro‑atherogenic and anti‑atherogenic cholesterol fractions. A lower ratio was considered favourable, reflecting fewer LDL particles relative to HDL particles. However, contemporary cardiovascular guidelines have moved

1. Overview: What this test reveals and why it is important Triglycerides are the main form of fat stored in the body and the most abundant dietary fat. They consist of three fatty acids attached to a glycerol backbone. In the bloodstream, triglycerides are carried within chylomicrons (from dietary fat) and very‑low‑density lipoproteins (VLDL, synthesised by the liver). A triglyceride measurement reflects the balance between energy intake, energy expenditure, and hepatic fat