Scientists have recently developed an assay to diagnose and monitor patients with low levels of immunoglobulin, including multiple myeloma patients. Immunoglobulin is a marker commonly used to diagnose and follow the progression of multiple myeloma. This new assay, which can detect low levels of serum immunoglobulin, is known as a free light chain (FLC) assay.

Measurements of immunoglobulin levels are often determined through several types of electrophoresis tests. While these techniques are sufficient for most patients, they are inadequate for more than 3% of patients with nonsecretory or light chain myeloma, which are characterized by the absence of intact immunoglobulin in both the serum and urine.

In healthy individuals and the majority of myeloma patients, an immunoglobulin is composed of two light chains bound to two heavy chains. In some patients, the light chains are separated, creating excess “free” light chains in their blood stream.

The serum FLC assay measures levels of two immunoglobulin light chains. Several recent studies have demonstrated that the FLC assay has increased sensitivity in detecting FLC in patients with nonsecretory myeloma or light chain multiple myeloma.

Several studies have recommended that baseline measurements taken during FLC assays be used for the prognosis of survival in patients with newly diagnosed multiple myeloma. An abnormal ratio between the two types of FLC predicts a higher rate of progression to active disease requiring treatment. In a study of patients with asymptomatic myeloma, patients with a normal FLC ratio had a five-year progression rate of 25 percent, compared to patients with an abnormal FLC ratio who had a five-year progression rate as high as 76 percent.

Although the FLC assay cannot yet replace other diagnostic techniques for patients with measurable urinary immunoglobulins, it may still eventually prove suitable for patients with intact immunoglobulin. Approximately 97 percent of these patients also produce excess serum FLC.

Serum FLC assays are more sensitive for early response and early relapse of disease than standard diagnostic tests, but it is not yet known whether the early detection of disease relapse has any impact on patient survival.

Since excess FLC is common to many plasma cell disorders, the FLC assay may also assist in earlier diagnosis of these disorders.

For more information, see the article “Serum Immunoglobulin Free Light Chain Assay in Myeloma” in the Fall 2008 issue of Myeloma Today (pdf).