Detecting Paraproteins
(December 2003)
(Download 
Detecting Paraproteins.pdf)
Paraproteins: What are they?
The term "paraprotein" means abnormal protein. Historically it refers to the detection of an additional band on protein electrophoresis migrating between the inter-a and post-g zones and the term has become synonymous with plasma cell production of monoclonal immunoglobulins. The paraprotein is characterised by identification of the heavy and light chain isotype of the immunoglobulin clone. This has prognostic significance, with lambda light chain associated with greater risk of nephrotoxicity, and IgM and IgG3 heavy chain isotypes associated with greater risk of hyperviscosity.
Conditions were paraproteins may be found
Myeloma
The most important clinical setting for the detection of a paraprotein is in the diagnosis of multiple myeloma. However, paraproteins also occur in clinical settings other than myeloma (Table 1), with greater than 90% being clinically "benign". The central question regarding the finding of any paraprotein is "Is this paraprotein malignant?". A number of clinical and laboratory parameters are used to address this question. Favourable features include lack of "immune paresis" (immunoglobulin reduction), lack of paraproteins in urine, low b2-microglobulin levels, and a paraprotein level of <10g/L (depending on class). However, only progress monitoring of a paraprotein, and consideration of bone marrow biopsy and skeletal survey to address plasma cell load, will detect all malignancy cases. Often the most valuable parameter is progress over time. A separate information sheet on "Investigation of Suspected Myeloma" is available from HAPS and on the HAPS web site.
Table 1: Conditions Associated with Monoclonal Proteins
| Multiple myeloma (m, g, a, d, e, light chains) |
| Waldenstroms Macroglobulinaemia (m only) |
| Heavy Chain Disease (g, m, a) |
| Lymphoma/Leukaemia (m, d) |
| Primary Amyloidosis |
| Non-Lymphoid Neoplasms |
| Liver Disease (usually associated with viral infection) |
| Chronic Infective or Inflammatory States |
| Autoimmune Diseases |
Monoclonal Gammopathy of Uncertain Significance (MGUS)
Low levels of monoclonal paraprotein are detected with increasing age, with up to 10% of individuals over 75 years old displaying these findings on protein electrophoresis screening. Labelled "Monoclonal Gammopathy of Uncertain Significance" (MGUS), this condition is frequently associated with normal health, but in 10% of people MGUS will evolve into myeloma.
Primary Amyloidosis
Amyloidosis is a condition where insoluble fibrous amyloid proteins are deposited diffusely in tissues throughout the body, causing disease largely through architectural distortion. Multiple varieties of amyloidosis exist, but this Communique will only discuss the subtype associated with paraproteinaemia: primary light-chain amyloidosis (AL amyloid). In AL amyloid, a monoclonal population of bone marrow plasma cells is present and consistently produces abnormally processed lambda or kappa light-chain fragments. In association with the acute-phase reactant serum amyloid protein (SAP), these immunoglobulin light chains are laid down in extracellular spaces, causing a range of clinical syndromes (Table 2). Less than 20% of patients with AL amyloid have myeloma. The other 80% of monoclonal gammopathies have light chain disease or agammaglobulinaemia (producing light chains, but not intact immunoglobulin). Conversely, about 15 to 20% of patients with myeloma have amyloidosis.
Table 2: Clinical Presentation of Primary Systemic Amyloidosis
| Monoclonal immunoglobulin in urine or serum plus any of these features. |
- Unexplained nephrotic syndrome
- Hepatomegaly
- Carpal tunnel syndrome
- Macroglossia
- Malabsorption or unexplained diarrhoea or constipation
- Peripheral neuropathy
- Cardiomyopathy
|
These paraproteins are often detectable in circulation, but they may be present at such low levels that only more sensitive laboratory methods, such as isoelectric focusing-immunofixation (IEF-IF), are required to detect them. When amyloidosis is suspected, the protein electrophoresis screening for paraproteinaemia may be negative and a request for serum and urine IEF-IF is recommended. Ultimately, the gold-standard for diagnosing amyloidosis is the demonstration of characteristic Congo-Red-birefringent fibrillar deposits on histological examination of biopsy specimens from effected tissues.
Laboratory Investigation Strategies for Paraproteins
If myeloma is suspected, the laboratory investigations set out in (Figure 1) are appropriate. In the setting of possible amyloidosis, where paraproteins may exist below the detection limit of protein electrophoresis, the more sensitive approach of serum and urine IEF-IF should be used if initial protein electrophoresis tests are negative (Figure 2).
Figure 1: Investigation of Possible Myeloma
Figure 2: Investigation of Possible Primary Amyloidosis
Sample Requirements
A spot urine sample and 1mL of serum is sufficient to assay all the tests listed for the investigation of paraproteins. Plasma is unsuitable as the anti-coagulants interfere with the measurement of immunoglobulins and fibrinogen appears as an extra band on protein electrophoresis that may be confused with or mask a paraprotein. Haemolysed serum can make interpretation of IEF bands difficult. Urine should be collected without any preservative and a 20mL aliquot of a spot or 24-hour collection is sufficient for all the urine tests listed.
About the Author
Dr Glenn Reeves, HAPS Immunology, is the primary author of this HAPS Communiqu. If you have any questions regarding this topic the Immunology staff would be happy to assist you on Telephone: (02) 49214000, Facsimile: (02) 49214400.