What is Serum Amyloid A (SAA) Test?
Serum Amyloid A (SAA) Test — Acute Phase Protein for Early Inflammation Detection
Serum Amyloid A (SAA, Amyloid A) is a key acute-phase protein that rapidly increases in response to inflammation, infection, or tissue injury. SAA is often used alongside CRP and is particularly useful for early inflammation detection, disease monitoring, and prognostic assessment in chronic inflammatory disorders.
1. Purpose of the SAA Test
The SAA test is indicated for:
- Early detection of acute inflammation
- Rapidly rises within hours after bacterial, viral infection, or tissue injury
- Sometimes reacts faster than CRP
- Monitoring chronic inflammatory diseases
- Rheumatoid arthritis (RA)
- Ankylosing spondylitis (AS)
- Inflammatory bowel disease (IBD)
- Psoriatic arthritis
- Assessing infection treatment response and prognosis
- Helps evaluate antibiotic effectiveness
- Evaluating secondary amyloidosis (AA amyloidosis) risk
- Persistent high SAA levels may lead to amyloid A deposition in kidneys or the gastrointestinal tract
2. Test Method: Latex Immunoturbidimetry
SAA is measured using latex immunoturbidimetry in most automated analyzers.
Principle:
- Latex particles coated with anti-SAA antibodies are mixed with patient serum.
- SAA binds to the antibodies, forming immune complexes.
- The increase in turbidity (light scattering) is measured spectrophotometrically and converted to SAA concentration.
Advantages:
- Rapid results (minutes)
- Suitable for automated systems (e.g., cobas)
- High sensitivity and specificity
- Excellent reproducibility
3. Reference Range
- Normal SAA: < 10 mg/L (varies slightly depending on instrument and reagent)
- Healthy individuals typically have very low SAA levels; levels rise sharply during inflammation or infection.
4. Clinical Significance
- Sensitive marker of acute inflammation
- Increases within 4–6 hours of inflammation onset
- Can reach hundreds of mg/L during infection
- Rapidly decreases during recovery (short half-life)
- Often rises faster than CRP
- Monitoring chronic inflammatory activity
- SAA is useful alongside ESR and CRP to track disease activity in RA and other chronic conditions
- Viral infections
- SAA may increase even when CRP remains low
- Example: SAA levels in COVID-19 patients can predict disease severity
- Secondary amyloidosis risk
- Prolonged elevated SAA exposure can lead to amyloid deposition and organ dysfunction
5. Conditions Associated with High SAA
- Infections: bacterial (pneumonia, sepsis), viral (COVID-19, influenza), tuberculosis
- Inflammatory/autoimmune diseases: RA, AS, IBD, psoriatic arthritis, SIRS
- Tissue injury: surgery, trauma, burns, myocardial infarction
- Malignancies: kidney, lung, liver cancers
- Chronic inflammation → increased risk of AA amyloidosis
6. Conditions Associated with Low SAA
- Generally, low SAA is normal
- May indicate:
- Absence of infection or inflammation
- Immunosuppressed state
- Severe hepatic dysfunction (decreased protein synthesis)
7. Summary Table
| Item | Description |
|---|---|
| Test Name | Serum Amyloid A (SAA, Amyloid A) |
| Purpose | Detect acute/chronic inflammation, early infection diagnosis, disease monitoring |
| Method | Latex Immunoturbidimetry (immune complex → turbidity measurement) |
| Reference Range | < 8–10 mg/L |
| Conditions with High SAA | Infection (bacterial/viral), autoimmune diseases, IBD, malignancy, tissue injury |
| Clinical Significance | Faster response than CRP, prognostic assessment, secondary amyloidosis risk evaluation |
References
- Uhlar CM, Whitehead AS. Serum amyloid A, the major acute-phase reactant. Eur J Biochem, 1999.
- Sack GH. Serum amyloid A — a review. Mol Med, 2018.
- Yamada T. Serum amyloid A in inflammatory diseases. Clin Chem Lab Med, 1999.
- Cojocaru M. Acute phase proteins in inflammatory disease. Rom J Intern Med, 2010.
- Jiang L, et al. Serum amyloid A levels in COVID-19 patients. J Infect, 2020.
- Roche Diagnostics. Package Insert: Amyloid A Latex Immunoturbidimetric Assay.