Glomerular Filtration Rate Estimation Using β2-Microglobulin 2-Microglobulin and β-Trace Protein in Adults With Solid Tumors: A Prospective Cross-Sectional Study

Rationale & Objective: beta(2)-Microglobulin (B2M) and beta-trace protein (BTP) are novel endogenous filtration markers that may improve the accuracy of estimated glomerular filtration rate (eGFR) beyond creatinine and cystatin C (eGFR(cr-cys)), but they have not been assessed in patients with cancer. Study Design: Cross-sectional analysis. Setting & Participants: Prospective cohort of 1,200 patients with active solid tumors recruited between April 2015 and September 2017. Exposure: CKD-EPI equations without race combining B2M and/or BTP with creatinine with or without cystatin C (2-, 3-, or 4-marker panel eGFR). Outcome: Performance of equations compared with eGFR(cr-cys) and non-GFR determinants of serum B2M and BTP (S-B2M, and S-BTP, respectively). Measured GFR (mGFR) was determined using the plasma clearance of chromium-51 labeled ethylenediamine tetraacetic acid (Cr-51-EDTA). Analytical Approach: Bias was defined as the median of the differences between mGFR and eGFR, and 1-P-30 was defined as the percentage of estimates that differed by more than 30% from the mGFR (1-P-30). Linear regression was used to assess association of clinical and laboratory variables with S-B2M, and S-BTP after adjustment for mGFR. Results: Mean age and mGFR were 58.8 +/- 13.2 SD years and 78.4 +/- 21.7 SD mL/min/1.73m(2), respectively. Performance of the 3-marker and 4-marker panel equations was better than eGFR(cr-cys) (lesser bias and 1-P-30). Performance of 2-marker panel equations was as good as eGFR(cr-cys) (lesser bias and similar 1-P-30). S-B2M and S-BTP were not strongly influenced by cancer site. Limitations: Participants may have had better clinical performance status than the general population of patients with solid tumors. Conclusions: B2M and BTP can improve the accuracy of eGFR and may be useful as confirmatory tests in patients with solid tumors, either by inclusion in a multimarker panel equation with creatinine and cystatin C, or by substituting for cystatin C in combination with creatinine.