Table of Contents
Detection of monoclonal light chains is crucial in the diagnosis of AL amyloidosis, since the disease is caused by aberrant plasma cells secreting a single type of immunoglobulin light chain that constitutes amyloid fibrils. The most widely employed conventional diagnostic methods are given below:
1. Serum Protein Electrophoresis (SPEP)
- Role: Identifies abnormal monoclonal proteins (M-proteins or paraproteins) in the blood.
- How it works: Splits proteins in the serum using electric current; the M-protein results as a sharp spike or band in the gamma area.
- Limitations: Can fail to detect low-level monoclonal proteins found in some amyloidosis patients.
2. Urine Protein Electrophoresis (UPEP)
- Purpose: Identifies Bence Jones proteins (free light chains) in a 24-hour urine collection.
- Often combined with: Immunofixation to establish monoclonality.
- Limitations: Needs proper urine collection for 24 hours; can be limited in sensitivity.
3. Immunofixation Electrophoresis (IFE)
- Purpose: Confirms and identifies the presence and type of monoclonal protein in serum and urine.
- Benefit: Substantially more sensitive than SPEP or UPEP in isolation.
- Importance: Is regarded as a gold standard for the detection of monoclonal immunoglobulin light chains.
4. Serum Free Light Chain (FLC) Assay
- Purpose: Measures kappa and lambda free light chains in the blood.
- Diagnostic clue: An abnormal kappa/lambda ratio is a strong indication of a monoclonal plasma cell disorder.
- Benefit: Can pick up disease even when conventional electrophoresis techniques are negative.
- Needed for: Follow-up of disease activity and response to therapy.
5. Bone Marrow Biopsy with Immunohistochemistry (IHC)
- Role: Examines the percentage of plasma cells and for clonal expansion.
- What’s tested: Light chain restriction (either kappa or lambda).
- Use: Often combined with cytogenetic and FISH (fluorescence in situ hybridization) testing for deeper evaluation.
6. Fat Pad or Tissue Biopsy with Congo Red Staining
- Purpose: Confirms amyloid deposits using Congo red dye, which shows apple-green birefringence under polarized light.
- Follow-up: If amyloid is confirmed, immunohistochemistry or mass spectrometry is used to identify the type of amyloid and determine whether it’s derived from monoclonal light chains.
Summary of Diagnostic Workflow
| Method | Sample | Purpose | Strength |
|---|---|---|---|
| SPEP | Blood | Detect M-protein | Quick screen |
| UPEP | Urine | Detect light chains | Detects Bence Jones protein |
| IFE | Blood & Urine | Confirm monoclonal protein | High sensitivity |
| FLC Assay | Blood | Quantify free light chains | Detects low-level disease |
| Bone Marrow Biopsy | Marrow | Identify plasma cell clone | Cellular confirmation |
| Tissue Biopsy + Congo Red | Fat pad/organs | Confirm amyloid deposits | Visual confirmation of amyloid |
FAQ: Detecting Monoclonal Components in Amyloidosis
Q1. What is the use of serum protein electrophoresis (SPEP)?
A: SPEP identifies abnormal monoclonal proteins (M-proteins) in blood but can miss low levels.
Q2. What does urine protein electrophoresis (UPEP) identify?
A: UPEP detects Bence Jones proteins (free light chains) in urine, helpful in AL amyloidosis.
Q3. Why is immunofixation electrophoresis valuable?
A: It identifies the presence and type of monoclonal protein and is more sensitive than SPEP or UPEP alone.
Q4. What is a serum free light chain (FLC) assay?
A: It measures kappa and lambda light chains in the blood and identifies imbalances that indicate monoclonal production.
Q5. Is a biopsy necessary?
A: Yes, tissue biopsy (such as fat pad or organ) with Congo red stain verifies amyloid deposits, and bone marrow biopsy identifies abnormal plasma cells.
Q6. How is Bone Marrow Examination helpful in diagnosing AL amyloidosis?
A: Bone marrow aspiration and biopsy help assess the plasma cell population, as AL amyloidosis often originates from an underlying