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Abstract: SA-PO1090

Importance of Adjusting the Normal Range of the k/L Free Light Chain Ratio According to the CKD Stage in Myeloma Patients

Session Information

Category: Pathology and Lab Medicine

  • 1502 Pathology and Lab Medicine: Clinical

Authors

  • Quintana, Luis F., Hospital Clinic de Barcelona. Fundacio Clinic per la Recerca Biomedica, Barcelona, Spain
  • Molina, Alícia, Hospital Clinic, Barcelona, Spain
  • Gacitua, Ignacio, University of Chile, Santiago, Chile
  • Guillen, Elena, Hospital Clinic, Barcelona, Spain
  • Montagud, Enrique, Hospital Clínic, Barcelona, Spain
  • Xipell Font, Marc, Hospital Clinic, Barcelona, Spain
  • Poch, Esteban, Hospital Clinic, Barcelona, Spain
Background

The development of an effective laboratory test to quantify the concentration of free light chains (FLC) has optimized the diagnosis of multiple myeloma (MM). However, the metabolism of FLC depends to a large extent on renal function, which can lead to a misinterpretation of the results. The objective of this study was to determine the concentration of serum FLC in a group of MM patients and a group of healthy patients, and to establish the variation of the FLC ratio normal range and its diagnostic performance for MM in relation to the CKD stage.

Methods

The FLC ratio κ/λ in serum and GFR was analyzed retrospectively by CKD-EPI in 1469 consecutive patients between December 2014 and December 2017. Two groups were chosen: 1) healthyand complete remission MM patients,(n=174); 2) patients with a diagnosis of active MM (n=416). The reported normal range of the FLC ratio is 0.26-1.65. We excluded patients with a diagnosis of MGUS or other hematological diseases. ROC analysis were made for these groups depending on the GFR and the Sensitivity/Specificity value obtained for each subgroup was compared. The optimal cut-off was established based on the maximum value of Sensitivity/Specificity.

Results

A MM diagnosis based on the initial FLC normal range has a specificity of 96% in the group with GFR>90 (n=244)79% in GFR 30-60 ml/min (n=87) and 43% in GFR<30 ml/min (N=45).The sensitivity and specificity of the FLC κ/λ ratio is maximum when we divide the patients in two groups (GFR < or > 55 ml/min) and apply an adjusted renal range (0.82 - 2.75):-for MM Kappa patients with GFR<55 ml/min, the initial Specificity/Sensibility of 87.7%/56.5% changed to 80.7%/95.6% while for MM Lambda patients with GFR<55 ml/min, the initialSpecificity/Sensitivity of 73.3%/100% changed to 96.7%/100%.

Conclusion

The FLC k/L ratio is a safe method for the study of selective proteinuria in MM in patients with normal renal function but, if we do not correct the FLC ratio as the GFR decreases, its specificity is reduced. The need for this correction is most likely due to the different clearance rates of the kappa and lambda FLC and how they change with GFR levels. Thus, it is necessary to take into account the GFR for its interpretation and validate this new renal range for CKD stage 4 and 5, in future studies.