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Kidney Week

Abstract: PO2428

The Effect of Kidney Function on Reference Intervals of Serum-Free Light Chains and Free Light Chain Kappa/Lambda Ratio

Session Information

Category: CKD (Non-Dialysis)

  • 2102 CKD (Non-Dialysis): Clinical, Outcomes, and Trials

Authors

  • Long, Thorir E., Haskoli Islands, Reykjavik, Iceland
  • Indridason, Olafur S., Landspitali, Reykjavik, Capital, Iceland
  • Palsson, Runolfur, Haskoli Islands, Reykjavik, Iceland
  • Harding, Stephen, The Binding Site, Birmingham, United Kingdom
  • Landgren, Ola, Sylvester Comprehensive Cancer Center, Miami, Florida, United States
  • Kristinsson, Sigurdur Y, Haskoli Islands, Reykjavik, Iceland
Background

A kidney reference interval has previously been published for serum free light chain (FLC) ratio (0.37–3.10) but does not take into account the degree of kidney failure. The aim of this study was to establish a kidney reference interval for FLC and validate the current and propose new kidney reference interval for FLC ratio.

Methods

A total of 80,759 participants of the Iceland Screens, Treats or Prevents Multiple Myeloma (iStopMM) study were included. Participants were screened with serum FLC (FREELITE) measurements and serum protein electrophoresis (SPEP) and immunofixation (IFE). Serum creatinine (SCr) value closest to the screening was used to calculate eGFR. Participants with M-protein, eGFR > 59 mL/min/1.73 m2, missing SCr measurement or > 1 year from the iStopMM screening were excluded. A nonparametric method was used to calculate the 95% CI. Partitioning was determined based on the proportion in each subgroup outside reference interval.

Results

Serum FLC were measured in 4885 (12%) participants with eGFR <60 mL/min/1.73 m2, without evidence of monoclonality on SPEP or IFE. Median (IQR) kappa level was 20.6 mg/L (16.0–27.7), lambda level 18.6 mg/L (14.7–24.2) and FLC ratio 1.13 (0.95–1.35). Using current reference intervals, 58% and 20% of persons had values outside the normal range for kappa and lambda, respectively. The FLC ratio was outside the standard reference interval (0.26–1.65) in 8% and the kidney reference interval (0.37–3.10) in 0.6% of persons. Based on these findings, new reference intervals for FLC and FLC ratio have been established (Table).

Conclusion

Current reference intervals for FLC and FLC ratio are inaccurate for patients with decreased kidney function. We propose new reference intervals for FLC and FLC ratio for use in patients with chronic kidney disease.

Reference intervals for kappa, lambda, and FLC ratio depending on kidney function
 New reference interval (2.5 - 97.5th percentile)
Kidney function (ml/min/1.73 m2)Kappa
(2.5–97.5 percentile)
Lambda
(2.5–97.5 percentile)
FLC ratio
(2.5–97.5 percentile)
eGFR 45 – 5910.0 – 45.39.2 – 37.70.63 – 1.88
eGFR 30 – 4411.8 – 67.610.2 – 50.70.67 – 2.05
eGFR < 3017.9 – 109.614.4 – 87.90.67 – 2.14

eGFR: estimated glomerular filtration rate

Funding

  • Government Support – Non-U.S.