Creatinine and kidney function

Creatinine is a waste product made by your muscles every day. Healthy kidneys filter it out of the blood and pass it into the urine, so the level in the blood gives a simple measure of how well the kidneys are working. When the kidneys filter less well, creatinine builds up and the blood level rises. Labs often use creatinine, with your age and sex, to calculate an estimated filtration rate, sometimes written as eGFR, and your team may also calculate a creatinine clearance to plan doses.

Kidney function is one of the commonest reasons a chemotherapy dose is changed or a cycle is delayed. Many cancer medicines, including cisplatin, carboplatin, methotrexate, ifosfamide and pemetrexed, are cleared by the kidneys or can affect them. If the kidneys are not filtering well, medicine can build up in the body and cause stronger side effects. A rise in creatinine can come from the treatment, but also from dehydration after vomiting or diarrhoea, some painkillers and antibiotics, infection, or a blockage to urine flow. This page explains the test. It cannot interpret your result, which your team must do.

Dehydration is a common cause

Vomiting, diarrhoea, poor drinking and hot weather can raise creatinine quickly, and it often improves once fluids are replaced.

Muscle size affects the number

People with more muscle make more creatinine, and people who have lost weight and muscle make less, which your team takes into account.

A change can be managed

Extra fluids, a dose adjustment, a short delay or a change of medicine usually allow treatment to continue safely.

It cannot tell you whether your creatinine result is acceptable or what it means for your treatment. The same number can be fine for one person and a concern for another, depending on muscle size, age, earlier results and the medicines planned. Your team interprets it alongside your whole picture.

It also cannot tell you whether your dose should change or your cycle be delayed. Your oncologist decides this using limits set for your specific medicines. Never adjust your treatment, fluids or other medicines based on a result alone.

Avoid over-the-counter painkillers

Ibuprofen, diclofenac and similar painkillers can harm the kidneys during chemotherapy. Ask your team which pain relief is safe.

Tell scan teams about your treatment

Contrast dye used in some CT scans can affect the kidneys. Scan teams may check creatinine first and give fluids.

Diabetes and blood pressure matter

Both can affect the kidneys over time. Keeping them well controlled protects kidney function during and after treatment.

Herbal and traditional remedies

Some herbal products can harm the kidneys or interact with chemotherapy. Tell your team about everything you take.

Protein powders and supplements

High-protein supplements and creatine products can change creatinine results. Mention them to your team.

Kidney effects can linger

After some medicines, kidney function may not fully return to where it was. Occasional tests after treatment may be advised.

Older adults need extra care

Kidney function naturally declines with age, and older people can have reduced function even with a creatinine result inside the range.

Follow the hydration plan

For medicines that affect the kidneys, drinking as advised before and after treatment is one of the best protections.

Keep your kidney results together

A record of creatinine over time helps your team see trends quickly and plan doses.

What to do next

Follow your hydration advice, tell your team about vomiting, diarrhoea or passing less urine, avoid kidney-harming painkillers and remedies, keep your reports together, and let your team interpret creatinine results and decide on any change to treatment.