Monitoring renal function during chemotherapy

Renal function is monitored during chemotherapy because chemotherapeutic drugs are excreted by the kidneys and are potentially nephrotoxic. Doses are adjusted according to the glomerular filtration rate (GFR), i.e. the more reduced the GFR, the lower the treatment dose. Plasma clearance of ⁵¹Cr-EDTA is a reliable indicator of GFR before and during treatment with potentially nephrotoxic drugs, but its measurement is costly. GFR can also be estimated using an algorithm that converts plasma creatinine concentration to GFR, e.g. the MDRD equation. The aim of this investigation was to evaluate the reliability of estimated GFR (eGFR) in detecting changes in GFR as assessed by the MDRD equation in cancer patients treated with nephrotoxic chemotherapeutic drugs.

We included all patients from the Department of Oncology undergoing chemotherapy who were referred to the Department of Nuclear Medicine for measurement of GFR by the ⁵¹Cr-EDTA plasma clearance technique at least four times during the study period of 12 months. The eGFR was calculated from plasma creatinine concentration and the MDRD formula. GFR was determined by the ⁵¹Cr-EDTA plasma clearance method.

In 48 patients with a mean age of 47 years, GFR decreased from 86 to 73 ml/min/1.73 m² (mean values, p < 0.002) from the first to the last measurement, whereas plasma creatinine concentration and eGFR remained unchanged. In 13 patients (27 %) the finding of a decreased GFR led to adjustment of the dose of the chemotherapy drug. Eight of the 13 patients with decreased GFR also had a reduced eGFR but five patients had a normal eGFR. These five patients would have been treated with the nephrotoxic drug at a dose that was too high.

Neither creatinine plasma concentration nor eGFR (MDRD) can be recommended as a replacement for measurement of GFR with the ⁵¹Cr-EDTA plasma clearance method in patients treated with nephrotoxic cytostatic drugs.