#4195 CAN A BLOOD TEST FOR MIDDLE MOLECULES BE USED TO MEASURE RESIDUAL KIDNEY FUNCTION TO PERFORM INCREMENTAL DIALYSIS?
Authors: Butt Usama , Vilar Enric , Sridharan Sivakumar , Farrington Kenneth 
Published: June 2023

Abstract

Background and Aims
Incremental dialysis involves combining residual kidney functions (RKF) with dialysis dose to individualise treatment, increasing the dialysis dose as RKF falls. Potential benefits include quality of life benefits, less treatment burden and health economic benefits. Kidney Disease Outcome Quality Initiative (KDOQI) recommends incremental haemodialysis may be performed when renal urea clearance (KRU) is &gt; = 2ml/min. To avoid underdialysis, incremental approach requires frequent interdialytic urine collections to monitor RKF, which can be inconvenient.
An easier assessment of RKF would likely increase the uptake of incremental dialysis. Blood levels of middle molecules (e.g Beta 2 Microglobulin (Beta2M) and Beta Trace Protein (BTP)) have been studied as predictors of RKF. However, their role in identifying patients for incremental dialysis have not been tested. There are a few published methods of predicting RKF using meddle molecules. A proposed simple method is identification of patients with KRU &gt; = 2 ml/min, based on having a blood middle molecules level below a certain cut-off. Alternatively direct prediction of KRU from middle molecule levels can be performed with an algorithm/equation.
We set out to establish if these methods may identify patients with significant RKF who can benefit from incremental dialysis.

Method
We conducted a retrospective analysis on the data from a multicentre feasibility randomised controlled trial to assess the impact of incremental versus conventional haemodialysis initiation. As a part of this trial 55 participants were followed up for up to 12 months with monthly RKF measurement using interdialytic urine collections. Monthly Beta2M and BTP measurements were also performed. We used (1) a published middle molecules-based KRU equation (2) published Beta2M cut-off levels, to predict RKF. We, then, compared the predicted RKF with conventionally measured RKF from urine collection. The focus was to establish reliability of these methods in identifying patients with KRU &gt; 2 ml/min, which is the recommended cut-off for incremental dialysis, and to identify where underdialysis might occur if these methods were used in clinical practice.

Results
The middle molecules-based KRU equation had 62% sensitivity and 84% specificity to identify those with KRU &gt;2, whereas a beta2M cut-off level of &lt;19.15mg/L had 78% sensitivity and 82% specificity. 6/55 (10.9%) participants would have had underdialysis whilst performing incremental dialysis guided by a middle molecules-based KRU equation and 7/55 (12.7%) would under dialyse using the Beta2M cut-off level to predict KRU. The predicted mean underdialysis that would occur using these methods was 0.2 – 0.3 standard kt/v units. Combining these methods with urine volume improved specificity and sensitivity. Beta2M level of &lt;19.15 mg/L and Urine volume of &gt;0.5 litre/day combined predicted KRU &gt;2 with 70% sensitivity and 98% specificity. In other words, only 1/55 (1.8%) patients would have had under dialysis if incremental dialysis were performed based on a combination of Beta2M cut-off and urine volume.

Conclusion
Blood Beta2M level, when combined with urine volume assessment reliably predicts adequate RKF to perform incremental dialysis safely. If dialysis patients can reliably estimate or measure their urine volume, this tool can potentially replace the need for cumbersome interdialytic urine collection to determine RKF and offer an easy way to perform incremental dialysis.