Urinary κ and λ immunoglobulin light chains in normoalbuminuric type 2 diabetes mellitus patients

Assessment of Serum Free Light Chains as a Marker of Diabetic Nephropathy; A Cross-Sectional Study in the Kumasi Metropolis

Aims

Although traditional tests such as serum urea, creatinine, and microalbuminuria have been widely employed in the diagnosis of diabetic nephropathy, their sensitivity and accuracy are limited because kidney damage precedes the excretion of these biomarkers. This study investigated the role of serum free light chains in the disease manifestation of diabetic nephropathy.

Materials and Methods

Using a cross-sectional design we recruited 107 diabetes mellitus out-patients who visited the Diabetes and Renal Disease Clinics at the Komfo Anokye Teaching Hospital, Manhyia District Hospital, and Suntreso Government Hospital all in Ghana from November 2019 to February 2020. Five (5) mls of blood was collected from each participant and analyzed for fasting blood glucose (FBG) urea, creatinine, immunoglobulin free light chains. Urine samples were obtained and analyzed for albumin. Anthropometric characteristics were also measured. Data were analyzed using descriptive analysis, analysis of variance (ANOVA) test, Tukey HSD post hoc, and Kruskal Wallis test. Chi-squared test was used to examine if there are significant associations with the indicators of interest. In addition, Spearman’s correlation was used to test for associations between appropriate variables. Receiver operating characteristic analysis (ROC) was also performed to assess the diagnostic performance of free light chains.

Results

The mean age of studied participants was 58.2 years (SD: ± 11.1), 63.2% were females and most of the participants were married (63.0%). The mean FBG of the studied participants was 8.0mmol/L (SD: ± 5.86), and the average duration of diabetes mellitus (DM) was 11.88 years (SD: ± 7.96). The median serum Kappa, Lambda, and Kappa: Lambda ratios for the studied participants were 18.51 (15.63-24.18), 12.19(10.84-14.48), and 1.50(1.23-1.86) respectively. A positive correlation was observed between albuminuria and; Kappa (rs=0.132; p=0.209), and Lambda (rs=0.076; p=0.469). However, a negative correlation was observed between albuminuria and K: L ratio (rs=-0.006; p=0.956).

Conclusions

The current study observed an increasing trend in the levels of free light chains and degree of diabetic nephropathy, although not statistically significant. The exploration of serum free light chains as a better marker of diabetic nephropathy showed very promising results but further studies are required to elucidate its predictive value as a diagnostic tool for diabetic nephropathy.

Audit of the Prevalence of Noncorrelation of Immunofixation with Protein Electrophoresis and Serum Free Light Chain Assays in Multiple Myeloma in a Tertiary Cancer Care Center

Multiple myeloma (MM) is diagnosed and monitored by correlating panel of test results including serum Protein electrophoresis (SPE), Immunofixation electrophoresis (IFE), serum Free Light chain (sFLC) measurements. This audit is aimed to evaluate the prevalence of non-correlation and discrepancies amongst the three investigations (SPE/IFE/sFLC) for assessment of MM. 106 MM patients were reviewed over 16 months in a tertiary cancer care center by the availability of 3 serum test results (SPE/IFE/sFLC). Patients were divided into 2 groups: group1, newly diagnosed MM patients who were yet to receive myeloma specific treatment (n = 48); and group2, already diagnosed MM patients on treatment and followup (n = 58). Treatment modalities included stem cell transplantation and standard chemotherapy regimens. Non-correlation between the three test results (IFE/SPE/sFLC) was observed (21% in group1 and 45% in group2). Three types of discrepancies were detected as follows: (a) IFE showing less number of restriction bands as compared to SPE (8.6% patients in group2); (b) SPE/IFE negative with an abnormal sFLC ratio (12.5% patients in group1 and 13.7% in group2); (c) SPE/IFE positive but normal sFLC ratio (8% in group1 and 22% in group2). To conclude, IFE may sometimes provide information that does not always correlate with either of the SPE or sFLC results due to different sensitivities, antigen-antibody interactions, or treatment. Hence, SPE plus sFLC may be more useful particularly for patients on follow-up while IFE plus sFLC may help screen the new patients. The judicious selection of the biochemical assays can effectively reduce the treatment cost in a developing country like India.

Challenging the conventional wisdom on diabetic nephropathy: Is microalbuminuria the earliest event?

Microalbuminuria, urine albumin-to-creatinine ratio >30 and less than <300 mg/g has widely been accepted as biomarker of early diabetic kidney disease (DKD). Based on absence of beta-2 microglobulinuria in earlier studies on microalbuminuria, its possible tubular origin has been dismissed. Microalbuminuria has been assumed as a marker of endothelial injury. Low-molecular-weight (LMW) proteins are smaller than albumin and less restricted by the glomerular filtration barrier. Normal individuals excrete no >10 to 20 mg/day low-molecular-weight proteins in urine, as they are absorbed in the proximal tubules. Thus, LMW proteinuria, or non-albumin proteinuria (NAP) is a reliable marker of tubular dysfunction in patients without glomerular involvement. In some cohorts of patients with diabetes (DM), tubular proteinuria preceded microalbuminuria, and similar to the findings reported by Han et al. in this issue of the journal, the tubular origin of these proteins was confirmed through correlations with the increased urinary concentrations of N‑Acetyl‑β‑d‑Glucosaminidase (NAG), a marker of tubular-lysosomal injury. Observations show significant NAP in the urine of DM patients without microalbuminuria; and that NAP correlates with NAG. In many studies it appears that NAP often precedes microalbuminuria, and is likely not the earliest biomarker of diabetic kidney disease. The conclusion that microalbuminuria is a biomarker of glomerular endothelial injury and that it is the earliest finding in DKD requires a re-appraisal. Data increasingly suggest that in early stages of DKD, NAP precedes microalbuminuria, and that microalbuminuria itself may be a consequence of impaired tubular reabsorption.

Association between urinary free light chains and progression to end stage renal disease in chronic kidney disease

Background

Patients with chronic kidney disease (CKD) are at an increased risk of developing end-stage renal disease (ESRD). We assessed for the first time whether urinary free light chains (FLC) are independently associated with risk of ESRD in patients with CKD, and whether they offer incremental value in risk stratification.

Materials and methods

We measured urinary FLCs in 556 patients with CKD from a prospective cohort study. The association between urinary kappa/creatinine (KCR) and lambda/creatinine (LCR) ratios and development of ESRD was assessed by competing-risks regression (to account for the competing risk of death). The change in C-statistic and integrated discrimination improvement were used to assess the incremental value of adding KCR or LCR to the Kidney Failure Risk Equation (KFRE).

Results

136 participants developed ESRD during a median follow-up time of 51 months. Significant associations between KCR and LCR and risk of ESRD became non-significant after adjustment for estimated glomerular filtration rate (eGFR) and albumin/creatinine ratio (ACR), although having a KCR or LCR >75^th centile remained independently associated with risk of ESRD. Neither KCR nor LCR as continuous or categorical variables provided incremental value when added to the KFRE for estimating risk of ESRD at two years.

Conclusions

Urinary FLCs have an association with progression to ESRD in patients with CKD which appears to be explained to a degree by their correlation with eGFR and ACR. Levels above the 75^th centile do have an independent association with ESRD, but do not improve upon a current model for risk stratification.