Case Reports

Can Serum Free Light Chains Be Used for the Early Diagnosis of Monoclonal Immunoglobulin-Secreting B-Cell and Plasma-Cell Diseases?

Patients who are undergoing multiple myeloma screening with serum protein electrophoresis and immunofixation, especially those with renal failure, also should receive serum free light chain testing to increase specificity and reduce false-negatives.

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Patients who are undergoing multiple myeloma screening with serum protein electrophoresis and immunofixation, especially those with renal failure, also should receive serum free light chain testing to increase specificity and reduce false-negatives.

Multiple myeloma (MM) is a devastating disease with an estimated 26,850 new cases in 2015 according to Surveillance, Epidemiology, and End Results data and no definitive chemotherapeutic cure.1 In 97% of cases, MM is defined by monoclonal hypergammaglobulinemia, in which a malignant plasma cell clone secretes a monoclonal globulin; the remaining cases are nonsecretors.2 Each pathologically produced clonal globulin contains 2 heavy chains attached by disulfide linkage and 2 light chains. Unchecked plasma cell production is what later causes the symptoms of renal failure, bone destruction, and anemia.

The rate of MM is disproportionately high in the veteran population, and the VA health care system provides care for many of these patients. The higher rate is likely secondary to the predominantly male population, which has higher MM rates, and has been linked to Agent Orange exposure in Vietnam. As MM is not easy to diagnose, any algorithm or testing method would be of great benefit to this population.

The gold standard for MM detection remains serum protein electrophoresis (SPEP) with immunofixation (IFE), but other detection methods have been emerging. The method of serum free light chain (SFLC) assay has become more readily available, and its incorporation into diagnostic guidelines has become more apparent but is not universal.3

In the case series reported in this article, SPEP/IFE and SFLC assays were used to test 207 patients from the VA New York Harbor Healthcare System (VANYHHS). All these patients had a clinical context for MM testing.

Methods

In this retrospective study, the authors reviewed the charts of VANYHHS patients who were being treated for conditions that prompted SPEP/IFE and λ and κ SFLC analysis between December 2013 and March 2014. The study was exempt from institutional review board approval.

The SPEP/IFE analysis was performed with an automated electrophoresis machine (Sebia Electrophoresis), and the SFLC analysis was performed with an automated SFLC assay (Freelite). Sensitivity, specificity, and positive and negative predictive values were calculated using SPEP/IFE as the gold standard and SFLC κ-to-λ ratio asthe test method. Patients with a positive κ-to-λ ratio but negative SPEP were considered false-positives. These patients’ SFLC analyses were further analyzed in an effort to evaluate use of the κ-to-λ ratio as an early tumor marker.

The κ reference range used was 3.3 to 19.4 mg/L, and the λ reference range used was 5.7 to 26.3 mg/L.4 The traditional reference range for the κ-to-λ ratio is 0.26 to 1.65.5

Results

Of the 207 patients in this study, 205 were men. Mean age was 69 years (range, 28-97 years). Mean serum urea nitrogen level was 8.75 mmol/L (range, 2.86-38.21 mmol/L), and mean creatinine level was 140.59 μmol/L (range, 44.21-1503.14 μmol/L). Mean κ was 49.82 mg/L (range, 4.6-700.96 mg/L), and mean λ was 54.27 mg/L (range, 3-1,750 mg/L). Table 1 compares the SPEP and SFLC data. Sensitivity was 67%, specificity was 85%, positive predictive value was 58%, and negative predictive value was 89%. Concordance of the 2 methods was 80%. The false-positive group was followed up 16 months later to check for diagnosis of disease. Two of the 24 patients in this quadrant were later diagnosed with MM (Table 1).

One of the patients with MM was an 82-year-old African American man with a history of hypertension, diabetes, and prostate cancer (Gleason 4 + 4 = 8/10). He presented to VANYHHS after a fall in which he sustained a pathologic fracture of the left acromion. Recurrent prostate cancer was initially suspected, and nuclear bone scintigraphy revealed increased uptake in the left shoulder and the posterior ninth rib. Results of computed tomography-guided biopsy showed the rib lesion packed with plasma cells and consistent with MM. Immunohistochemical analysis was positive for CD138 and κ in the malignant plasma cells. Initial SPEP performed before the biopsy showed an acute phase reaction with hypogammaglobulinemia, and SPEP after the biopsy showed an increased α-2 band but no monoclonal gammaglobulinopathy. The initial κ of 42.18 mg/L (κ-to-λ ratio, 4.01) was up to 67.53 mg/L 4 months later.

The other patient with MM was a 91-year-old man who had coronary artery disease after undergoing coronary artery bypass grafting in 1993, sick sinus syndrome after pacemaker implantation, hypertension, and anemia. He initially presented to the geriatrics clinic with polyneuropathy, which prompted SPEP and SFLC analysis. SPEP results showed a normal electrophoretic pattern, but κ increased to 47.52 mg/L (κ-to-λ ratio, 2.63). The decision was made to monitor the patient in the hematology clinic. Subsequent κ chain analysis revealed an increase to 59.50 mg/L. A repeat SPEP, performed 1 year after the first SPEP, revealed monoclonal immunoglobulin A on IFE.

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