# Accuracy of glomerular filtration rate estimates among patients with cancer

## TL;DR

This study finds that combining creatinine and cystatin C gives the most accurate kidney function estimates for cancer patients, improving treatment dosing.

## Contribution

The study introduces the combined eGFRcr-cys as a more accurate GFR estimation method for cancer patients compared to creatinine-only methods.

## Key findings

- eGFRcr-cys provided the highest accuracy in estimating measured GFR in cancer patients.
- Using eGFRcr could lead to carboplatin overdosing in 10–20% of patients.
- Combining creatinine and cystatin C reduced overdosing risks by 3–4 times compared to eGFRcr.

## Abstract

Glomerular filtration rate (GFR) estimation is a key issue in determining cancer treatment eligibility and dosing of treatments with narrow therapeutic index. Yet, little is known about the accuracy of GFR estimation among people with cancer in routine care.

In a cross-sectional study including 1611 adults with cancer referred for 1837 determinations of measured GFR (mGFR), we assessed the accuracy of estimated GFR based on creatinine (eGFRcr), cystatin C (eGFRcys) and their combination (eGFRcr-cys). Accuracy was reported as percentage of patients with estimated values within 30% of mGFR; bias and precision as the median and interquartile range of eGFR-mGFR, respectively. Dosing accuracy was assessed by calculating expected dose of carboplatin for area under the curve of 5 mg/mL/min using the Calvert formula.

Median age was 68 (IQI 61 to 74) years, 38.5% were female with mean mGFR 75 (SD 30) mL/min; 17% had metastatic disease. Accuracy, bias and precision were best for eGFRcr-cys. Using eGFRcr would recommend an “overdose” of carboplatin in 10–20% of participants: this was 3–4 times less common using eGFRcr-cys.

eGFRcr-cys equations provide the most accurate estimates of mGFR in patients with cancer, with potential to improve dosing accuracy substantially compared to eGFRcr.