Introduction

Bence Jones protein refers to a urinary protein that leaves the solution at approximately 56^oC under particular conditions of ionic strength and pH and returns to the solution on further heating to 100^oC. It represents a homogeneous population of kappa or lambda-type light chains. The presence of these immunoglobulin light-chain proteins in the urine is linked to several systemic diseases.

Bence Jones protein (BJP) was first described in 1845 in a patient admitted to St. George’s Hospital in London with vague continuous pain in the chest, back, and pelvis. Dr. Henry Bence Jones tested the patient's urine and found a substance precipitated by adding nitric acid. Jones proceeded to call this substance “hydrated deutoxide of albumen.” All types of proteinuria were referred to as albuminuria at that time. The autopsy of this patient revealed that his sternum and vertebrae were soft and fragile, and multiple hemorrhagic cavities were present in the bone. The cause of death was noted to be “atrophy from albuminuria.” The term Bence Jones protein was first used in 1880 by Dr. Fleischer.[1] Its peculiar characteristics on heating first characterized BJP: precipitation of the urine at 40 to 60^oC and re-dissolving of the precipitate at 100^oC.[2][3]

While this seminal observation led to the first description of multiple myeloma (MM), it did not hold up to scrutiny over time. Today BJP is known as the light chain of immunoglobulins without the accompanying heavy chain and can be accurately quantified by electrophoretic techniques, including immunofixation electrophoresis (IFE). The other crucial teaching point is that BJP is undetectable by dipsticks used to detect proteinuria since they detect albumin and not BJP.[4] In this brief review, we describe the evolution of BJP, its biochemistry, and its high clinical relevance.

In 1939 Longworth applied electrophoresis for the first time in the study of multiple myeloma. In 1953 Grabar and Williams described the methods of immunofixation and direct immunoelectrophoresis, which increased the detection of small monoclonal light chains not detectable on basic gel electrophoresis; this is the classic “M spike” seen in the gamma region in patients with MM. In 1956, Korngold identified the two classes of BJP: Kappa and Lambda light chains.[5]

In 1962, Drs. Edelman and Porter received the Nobel Prize in Physiology or Medicine for their work elucidating the chemical structure of antibodies. The M-spike of a particular patient with MM was broken into heavy and light chains. Edelman demonstrated that the light chains of this M-spike were identical to the BJP that the patient excreted in his urine. He expanded on this work by comparing reduced myeloma proteins from different patients. When each of these proteins was reduced, alkylated, and put through starch gel electrophoresis, they exhibited a unique migration pattern. Similar to BJP, when Edelman heated samples containing light chains from normal human serum gamma globulins, they became insoluble and re-solubilized with continued heating. In 1967, Dr. Putnam demonstrated that different BJPs had distinct peptide sequences. This differentiation further supported Dr. Edelman’s observation that no two BJPs “had the same mobility pattern.”[3]

Bence Jones protein, or free light chains, are found in the urine as low molecular weight monomers, dimers, or high molecular weight polymers. Contrastingly, Bence Jones proteins are present in the serum as tetramers. Their molecular weight is approximately 22000 Daltons, and the kidney metabolizes them through glomerular filtration, proximal renal tubular absorption, and renal catabolism. Bence Jones proteins spill into the urine once the capacity for tubular reabsorption becomes saturated.[6]

Specimen Collection

A clean catch early morning urine sample is needed to screen for Bence Jones proteins by urine protein electrophoresis and immunofixation electrophoresis. A 24-hour urine collection is desirable to quantify the amount of BJP accurately since it aids in diagnosing multiple myeloma. This specimen requires no preservative and can be kept at room temperature.[7]

Procedures

Methods for detection of Bence Jone proteins include conventional high-resolution electrophoresis or capillary zone electrophoresis followed by confirmation through immunofixation electrophoresis (preferable) or immunoelectrophoresis.

The various electrophoretic methods are conducted on agarose and cellulose acetate medium. Differences between these methods arise regarding the volume of the sample loaded and the sensitivity of the protein stain utilized. Depending on these characteristics, the urine must be concentrated before analysis to ensure appropriate sensitivity. Coomassie Blue and Colloidal Gold are the stains used to detect Bence Jones proteinuria. Colloidal Gold is the most sensitive stain but has drawbacks such as demanding technique and lack of stoichiometry between uptake by BJP and by other proteins.[6]

After gel electrophoresis, follow-up immunofixation electrophoresis serves to identify the type of BJP (kappa or lambda) and is the most sensitive measure of BJP. Immunofixation electrophoresis follows with antisera to IgG, IgA, IgM, total kappa, and total lambda. In monoclonal protein visualization without a corresponding heavy chain, additional immunofixation gel with antisera to delta and epsilon heavy chains can be performed, but it is not cost-effective. The issue of antigen excess with immunofixation electrophoresis can be minimized through decreased initial antigen loading. Immunoblotting is an alternative to immunofixation electrophoresis but is more cumbersome and uncommon in clinical laboratories.[8][6]

An advancement in the field is the ability to accurately measure free light chains by immunoassay and express them as a ratio. This test, the free light chain assay, is now used routinely to diagnose and monitor patients with plasma cell dyscrasias.[9] The International Myeloma Working Group now suggests using serum free light chain (sFLC) assay instead of urine protein electrophoresis and immunofixation electrophoresis if multiple myeloma is suspected. Quantitative free light chain assays utilize antisera directed against epitopes exposed only when light chains are free. Kappa and lambda free light chain concentrations are quantified, and the ratio of kappa to lambda is used to determine unbalanced light chain synthesis.

The free light chain assay is a significant addition to the clinical management of plasma cell dyscrasias due to its increased sensitivity for determining serum free light chains compared to previous methods. It also is a better marker of early remission and early relapse of multiple myeloma and a prognostic marker for identifying the risk of progression of monoclonal gammopathy of undetermined significance and smoldering myeloma. Its short physiologic half-life allows the free light chain assay to be a valuable tool for real-time monitoring for response to treatment and disease progression.[10] However, the sFLC assay has pitfalls, including the prozone phenomena of antigen excess, excess variability, and nonlinearity; hence, the IFE of urine is a valuable test for light chains.[11]

Overall, in light of the discussion of these various procedures, utilization of serum protein electrophoresis and free light chain assay will diagnose 100% of cases of multiple myeloma. This combination of testing poses a cost-effective and accurate modality for many laboratories worldwide.[10] However, the immunofixation electrophoresis detection of BJP, commonly lambda light chains, is still required to detect amyloidosis.[8]

Indications

Bence Jones proteins are a marker used to diagnose and monitor certain diseases, such as multiple myeloma. Therefore, providers need to be aware of the symptoms and signs of such conditions so that BJP can be tested and an appropriate diagnosis can be made. 

Symptoms of the underlying systemic disease may include the following:

• Weakness, lethargy, or fatigue
• Weight loss
• Anorexia
• Bone pain[12]
• Symptoms of peripheral neuropathy, such as numbness and burning pain
• Symptoms of compression fracture
• Recurrent infections[13]

Normal and Critical Findings

Quantitation of Bence Jones proteins occurs through electrophoresis and densitometry. Laboratory analysis of urine can identify Bence Jones proteins at a threshold of 10 mg/L. However, it is important to note that detection limits for Bence Jones proteins can only be approximate. The presence of Bence Jones proteins in the urine is usually considered abnormal and should raise suspicion for multiple myeloma or other plasma cell disorders.[6]

The serum free light chain (FLC) assay is quickly becoming the test of choice for detecting free light chains. This assay measures free kappa or lambda light chains. The reference range for the kappa to lambda light chain ratio is 0.26 to 1.65. An increase in the ratio denotes increased kappa light chains; a decreased ratio means an excess of lambda.[10] However, as stated above, this assay has several pitfalls.

Complications

The presence of light chain ladders in samples is a complicating phenomenon. Polyclonal light chains, usually kappa, can produce a characteristic banding pattern after electrophoresis and immunofixation electrophoresis. These light chain ladders are not Bence Jones proteins but commonly appear in the urine samples of elderly patients suffering from tubular proteinuria due to inflammatory disease. Moreover, Bence Jones proteins can sometimes co-migrate with the bands in these ladders. These ladders must be carefully examined to ensure no concomitant accompanying Bence Jones proteins. However, the clinical presentation and other investigative findings help confirm the presence of the BJP.[6]

Clinical Significance

Testing for Bence Jones proteinuria is indicated when plasma cell disorders such as multiple myeloma are suspected. Signs and symptoms that may prompt testing include anemia, hypercalcemia, and renal impairment. Bone manifestations such as painful lytic lesions, vertebral crushing, and long bone fractures are also indications. Increased suspicion for disorders such as multiple myeloma may also be prompted by symptoms of hyperviscosity like blurred vision, headaches, and epistaxis, as well as increased susceptibility to infection. Unfortunately, patients will often initially present with nonspecific symptoms such as fatigue and back pain, which can delay diagnostic testing, such as assessing urine for Bence Jones proteinuria.[14]

At least 60% of patients with classical myeloma have BJP in their urine. More importantly, 20% of patients with multiple myeloma produce only Bence Jones proteins without heavy chains. Excessive secretion of Bence Jones proteins causes acute kidney injury from tubular obstruction and tubulointerstitial inflammation, termed tubular nephropathy. Tubular damage results in Fanconi syndrome with glycosuria, aminoaciduria, phosphaturia, and renal tubular acidosis type 2.[14]

The presence of Bence Jones proteinuria significantly raises suspicion for multiple myeloma and warrants referral to a hematology clinic. Bone marrow aspiration for plasma cells and investigation for BJP are also significant markers of prognosis and disease progression. Plasma cells in multiple myeloma can present in various forms, including a mature, normal plasma cell, demonstrating features of immaturity such as a low cytoplasmic-nuclear ratio or loose chromatin, or present as bizarre “flame cells” with red cytoplasm. Bone marrow in patients with multiple myeloma generally is hypercellular and infiltrated diffusely by plasma cells.[15] Clonal bone marrow plasma cells equal to or greater than 10%, or biopsy-proven or extramedullary plasmacytoma, are criteria for diagnosing multiple myeloma.[16]

More specifically, changes in the urinary light chain excretion level can assess response to therapy. Direct positive effects on the treatment of multiple myeloma are defined as a reduction to 50% or less of the pretreatment value of urinary M-protein.[14] In patients with Waldenström macroglobulinemia and amyloidosis, BJP can be crucial in the diagnosis. In amyloidosis, immunofixation electrophoresis is superior to the serum FLC assay for detecting light chains.[8]

Testing for BJP and interpreting its clinical implications is best accomplished by an interprofessional team that includes multiple healthcare professionals, including physicians, nurse practitioners, physician associates, nursing (particularly oncology nurses), and laboratory personnel. [Level V]