Crp Aso titre which test are these
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CRP C-reactive protein ASO titre test types uses clinical significance
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Here is a clear breakdown of both tests:
CRP (C-Reactive Protein) Test
Type: Serum blood test - Acute Phase Reactant / Inflammatory marker
What it is: CRP is a pentameric protein synthesized by the liver in response to inflammation, particularly triggered by cytokines like IL-6. It acts as an opsonin and gets its name from reacting with the "C" carbohydrate antigen of Streptococcus pneumoniae.
Normal value: < 1 mg/L (high-sensitivity CRP); < 6-10 mg/dL (standard)
Why it is ordered:
- Detecting acute or chronic inflammation
- Monitoring bacterial infections (rises faster than ESR)
- Rheumatoid arthritis, SLE, and other autoimmune conditions
- Post-surgical infection monitoring
- Cardiovascular risk assessment (high-sensitivity CRP / hs-CRP)
- Acute pancreatitis (most useful 24-48 hours after admission)
- Periprosthetic joint infection screening
Key features:
- Rises faster and falls faster than ESR
- Sensitive but nonspecific marker of inflammation
- Increased in bacterial infections, tissue necrosis, malignancies, and inflammatory conditions
ASO Titre (Anti-Streptolysin O Titre)
Type: Serum blood test - Serological/immunological test for prior streptococcal infection
What it is: Measures the level of antibodies (IgG) formed against Streptolysin O, a toxin (exotoxin) produced by Group A beta-haemolytic Streptococcus (Streptococcus pyogenes). A raised titre indicates a recent or past streptococcal infection. The antibody blocks haemolysis by Streptolysin O but does not indicate immunity.
Normal value: < 200 IU/mL in adults; < 150 IU/mL in children (varies by lab)
Why it is ordered:
- To confirm recent Group A streptococcal (GAS) infection
- Diagnosis and monitoring of Acute Rheumatic Fever (ARF)
- Post-streptococcal glomerulonephritis (PSGN) - serial titres showing a twofold rise are highly indicative
- Suspected streptococcal complications (rheumatic heart disease)
Key note: Anti-DNase B is also used alongside ASO for pharyngeal infections; ASO may be less elevated in streptococcal skin infections (impetigo).
How They Relate
| Feature | CRP | ASO Titre |
|---|---|---|
| Type | Acute phase reactant | Streptococcal antibody test |
| Produced by | Liver | Immune system (B cells) |
| Rises in | Any inflammation/infection | Only after Strep A infection |
| Specificity | Non-specific | Specific to Strep A |
| Used together in | Acute Rheumatic Fever (ARF) | Acute Rheumatic Fever (ARF) |
| Normalizes | Quickly (days) | Slowly (months) |
Both tests are commonly ordered together in suspected Acute Rheumatic Fever (ARF) along with ESR, as per Jones Criteria, where they serve as evidence of a preceding streptococcal infection and ongoing inflammation.
- Harrison's Principles of Internal Medicine 22E and Robbins & Kumar Basic Pathology confirm CRP is an acute-phase reactant synthesized by the liver, acting as a sensitive but non-specific marker.
- Harrison's and Roitt's Essential Immunology confirm that elevated ASO titre indicates recent streptococcal infection and is used in diagnosing ARF and PSGN.
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