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Kidney Cancer · Diagnosis & Tests
Kidney function tests before treatment — what creatinine and eGFR actually tell your team
Kidney function tests before surgery are planning tests, not bad news. When a kidney tumour is found, your team needs to know how much filtering reserve you have before deciding anything — so a creatinine before nephrectomy, the eGFR calculated from it, and a urine test are requested early. Most people diagnosed with kidney cancer have entirely normal results, because the other kidney compensates. This page explains what each number means, what moves it, and which decisions it changes.
- A baseline, not a verdict — the reading taken before treatment is the line every later result is measured against.
- eGFR is an estimate — muscle mass, body weight, hydration, illness and several everyday medicines all move it, so one reading is never read alone.
- It shapes three decisions — whether the operation can spare kidney tissue, how contrast scans are made safe, and how systemic treatment is dosed and monitored.
- In-house at CION — the bloods, the urine tests, the scans and the ongoing monitoring sit with our own team, and the numbers are explained to you rather than filed.
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First, the context
What kidney function tests measure — and why they come before any decision
Being sent for these tests is routine. A tumour in one kidney does not usually reduce filtering, because the other kidney takes up the load, which is why so many people diagnosed with kidney cancer have entirely normal creatinine and eGFR. The tests are not looking for the cancer — the scan does that. They are measuring the reserve you are starting from, so that whatever is planned next can be planned safely. Our kidney cancer guide covers the diagnosis as a whole; this page stays with the function numbers.
Creatinine is a waste product your muscles make every day and your kidneys clear. If filtering falls, creatinine rises. On its own, though, it is a blunt yardstick: a well-muscled adult and a frail one with the very same filtering will not have the same creatinine, and dehydration, a heavy protein meal, a recent illness or a new medicine can all nudge it. That is why almost no team reads creatinine as a bare number any more.
eGFR — estimated glomerular filtration rate — is what the laboratory calculates from your creatinine together with your age and sex, reported as millilitres filtered per minute, adjusted for body size. It is the number most doctors actually use. Laboratories flag a result under 60, because that is the threshold used to define chronic kidney disease, but the definition also requires it to be sustained over about three months. One reading below the line is a prompt to repeat the test and look at the urine, not a diagnosis, and certainly not a reason to assume treatment is off the table.
The urine tests matter as much as the blood. Protein in the urine, usually reported as an albumin-creatinine ratio, tells your team whether the filters are leaking as well as how fast they are working, and it changes the interpretation of a borderline eGFR completely. A urine microscopy also picks up blood that is not visible to the eye. What each of these bottles is for is set out on our page on blood and urine tests in kidney cancer.
How much comes from each kidney. The total is only half the question when one kidney may be operated on. The contrast CT already shows the size, shape and blood supply of the kidney that is not affected, and that is often enough. Where it is not — a solitary kidney, both kidneys involved, or function that is already reduced — a nuclear-medicine split-function scan can measure how the work is divided between the two. That scan, like PET-CT, is coordinated for CION patients with specialist partner centres and may be billed there.
Where these tests happen. The bloods, the urine tests, the ultrasound, contrast CT and MRI, any biopsy, and the monitoring that follows are all delivered in-house at CION and read with you by a medical oncologist. Kidney surgery, robotic surgery, ablation and PET-CT are coordinated for you with specialist urology, uro-oncology and interventional radiology partners, and may be billed at the partner centre. NCCN guidance expects baseline function to be documented before treatment planning, which is exactly what these tests are for.
Five things move a creatinine or eGFR result without your kidneys having changed at all. Any of them is worth mentioning before you accept a number as your new normal:
- Dehydration. Fasting for a scan, a hot day, vomiting or poor intake all concentrate the blood and push creatinine up temporarily.
- Muscle mass and body size. More muscle means more creatinine at the same filtering rate; significant weight loss can flatter the number and hide a real fall in function.
- Medicines. Anti-inflammatory painkillers, some blood-pressure tablets, certain antibiotics and some supplements all shift the result. Bring your full list, including anything bought over the counter.
- Being unwell on the day. Infection, fever, a recent contrast scan or a spell in hospital can all produce a one-off reading that recovers.
- Which formula the laboratory used. Different laboratories report eGFR with different equations, so comparing a result from one lab against another can create a fall or a rise that never happened.
If a number on your report has worried you and nobody has explained it, ask. Book a free consultation and have your bloods, your urine result and your scan gone through together.
Did you know?
A single creatinine result is a snapshot, not a verdict. Because eGFR is calculated from creatinine, anything that moves creatinine — dehydration, muscle mass, weight loss, a new painkiller, being unwell on the day of the test — moves the eGFR with it. The trend across several readings, alongside your urine protein result, is what your team is really reading.
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Every kidney case at CION goes to a tumour board before anything is booked, and your results are explained to you, not filed. Free first consultation, and no commitment to start treatment.
Test by test
The kidney function panel — what each test measures and what it can change
Read this to follow the conversation you are about to have, not to interpret your own report. Only a doctor who has seen your results, your medicines and your scans can say what a number means for you.
| Test | What it measures | What the result can change |
|---|---|---|
| Serum creatinine | A muscle waste product cleared by the kidneys. Rises as filtering falls, but is also moved by muscle mass, weight and hydration. | Provides the raw value the eGFR is calculated from, and becomes the baseline that every reading after treatment is compared against. |
| eGFR (estimated filtration rate) | An estimate of filtering, calculated from creatinine with your age and sex and adjusted for body size. | Sets the safe boundaries for contrast scans, weighs the choice between kidney-sparing and whole-kidney surgery, and guides the dose and monitoring of systemic treatment. |
| Urine protein / albumin-creatinine ratio | Whether the filters are leaking protein, which is a separate question from how fast they are working. | Changes how a borderline eGFR is read, and often triggers a nephrology opinion alongside the cancer plan. |
| Urine dipstick and microscopy | Blood that is not visible to the eye, infection, and cells shed into the urine. | Can prompt further urological assessment, and infection is treated before any planned procedure. |
| Electrolytes and calcium | Sodium, potassium and calcium handling, which the kidneys control. | A raised calcium is followed up in its own right, and abnormal potassium is corrected before surgery or anaesthesia. |
| Full blood count | Haemoglobin and platelets. Anaemia is common in kidney cancer and in reduced kidney function alike. | Anaemia is investigated and corrected before an operation, and platelets and clotting have to be adequate before a biopsy. |
| Contrast CT of the kidneys | The tumour itself, and the size, shape and blood supply of the other kidney. | Often answers the split-function question on its own, and shapes whether kidney-sparing surgery is technically possible. |
| Split-function renogram | How the filtering work is divided between the two kidneys, when the CT alone leaves that unclear. | Used for a solitary kidney, disease in both kidneys or already-reduced function. Coordinated with specialist partner centres and may be billed there. |
| Blood pressure and diabetes control | The two commonest long-term causes of reduced kidney function, running alongside the cancer. | Tightening both protects the kidney tissue you are keeping, and is part of the plan before and after treatment. |
The bloods, urine tests, ultrasound, contrast CT, MRI, biopsy and follow-up monitoring on this list are delivered in-house at CION. The split-function renogram, PET-CT, ablation and kidney surgery are coordinated for you with specialist partners and may be billed at the partner centre. We put an indicative cost in writing before anything is booked, and check Aarogyasri, CGHS, ESI and insurance eligibility with you first.
Before, during and after
How your kidney function is checked — and protected — through treatment
None of these steps should happen without being explained to you, and you are entitled to your own numbers at every one of them.
Establish the baseline before anything is booked
Creatinine and eGFR, urine protein and microscopy, electrolytes, calcium, a full blood count and clotting, alongside your blood pressure, weight and diabetes control. If a result is borderline, it is repeated rather than acted on, and any correctable cause is dealt with first. This is the line every later reading is compared against, so it is worth getting right.
Make the scans safe
Iodinated contrast is what makes a kidney mass show up properly on CT, so it is not dropped lightly. Where function is reduced, the radiologist may give fluids before and after, use the smallest useful dose, pause medicines that stress the kidneys around the scan date, or move to MRI or ultrasound. MRI contrast has its own limits at very low function, so neither route is automatically safer.
Weigh the operation against the reserve
Function is one of the main reasons a kidney-sparing partial nephrectomy is preferred over removing the whole kidney, especially with a solitary kidney, disease in both kidneys, reduced eGFR, diabetes or long-standing high blood pressure. All kidney surgery, including robotic and laparoscopic approaches, is coordinated for CION patients with specialist urology and uro-oncology partners and may be billed at the partner centre.
Set up systemic treatment or radiation around it
Where medicines are needed, the immunotherapy and targeted classes used in kidney cancer are chosen, dosed and monitored with your function in mind, and bloods are taken before each cycle. Radiation is planned to spare healthy kidney tissue. Both are delivered in-house by our own medical and radiation oncology teams; which class applies to which situation is set out on our kidney cancer treatment in Hyderabad page.
Watch the trend afterwards, not the single reading
Creatinine is repeated in the days after an operation and again at follow-up, and function is monitored alongside surveillance scans. A drop straight after surgery is expected as the remaining kidney adapts; what matters is where the number settles and which way it moves over months. What to expect is set out on our page on kidney function after nephrectomy.
What these tests cannot do. They cannot tell you whether a mass is cancer, how big it is or whether it has spread — that is the scan's job, and sometimes the pathologist's. A normal eGFR does not rule kidney cancer out, and a low one does not mean the cancer is worse. They also cannot be read across laboratories without care, because different equations give different numbers. Their whole value is in the trend and in the decisions they inform, which is why they are repeated rather than admired once.
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Common questions
Questions people ask about kidney function tests
What kidney function tests are done before kidney cancer surgery?
A blood creatinine, with an eGFR calculated from it, is the core test. It is done alongside a full blood count, electrolytes, calcium, liver tests and clotting, and a urine test that looks for protein and for blood that is not visible to the eye. Your blood pressure, your weight and any diabetes control are recorded too, because they shape how the kidneys are likely to cope. Where a kidney may need to be removed, the team also wants to know how much of your filtering comes from each kidney separately; the contrast CT answers part of that, and a nuclear-medicine split-function scan is arranged where it does not. At CION the bloods, the urine tests and the imaging are delivered in-house.
What does eGFR mean in kidney cancer?
eGFR is an estimate of how much blood your kidneys filter each minute, worked out from your blood creatinine together with your age and sex, and reported as millilitres per minute adjusted for body size. It is an estimate rather than a measurement, so muscle mass, a very high or very low body weight, acute illness and several common medicines all move creatinine and therefore move the number. Laboratories flag a result under 60 because that is the threshold used to define chronic kidney disease, but one low reading is not a diagnosis; it has to be sustained over about three months and read alongside your urine protein result. In kidney cancer it matters because it sets the safe boundaries for contrast scans, for surgery and for systemic treatment.
Why is creatinine checked before a nephrectomy?
Removing a kidney, or part of one, removes working filtering tissue, so your team needs to know what you are starting with. The creatinine and eGFR taken before the operation become the baseline that every later result is compared against. They are also one of the things that push the decision towards a kidney-sparing partial nephrectomy rather than removing the whole kidney, particularly if function is already reduced, if you have only one working kidney, or if you live with diabetes or long-standing high blood pressure. The same numbers guide fluid and anaesthetic decisions and which medicines are paused around the operation. At CION the pre-operative bloods and imaging are ours; the surgery itself is coordinated with specialist urology and uro-oncology partners and may be billed at the partner centre.
Can I still have a CT scan with contrast if my kidney function is low?
Usually yes, and the decision is made on a current eGFR rather than on a rule of thumb. Iodinated contrast is what makes a kidney mass show up properly on CT, so it is not dropped lightly. Where function is reduced, the team may give fluids before and after the scan, use the smallest useful dose of contrast, pause medicines that stress the kidneys around the scan date, or choose MRI or ultrasound instead. The contrast used for MRI has its own limits at very low function, so neither scan is automatically the safer one. This is a judgement for the radiologist and your oncologist together, with a recent creatinine in front of them. It is not a reason to quietly cancel the appointment.
Does kidney cancer itself cause a high creatinine?
Not usually, which surprises most people. A tumour in one kidney does not normally push creatinine up, because the other kidney compensates, and that is why many people diagnosed with kidney cancer have entirely normal function tests. A raised creatinine more often reflects something running alongside the cancer: long-standing high blood pressure, diabetes, dehydration, blocked urine outflow, regular anti-inflammatory painkillers, or a tumour large enough to obstruct or invade. The reverse is equally true. A normal eGFR does not rule kidney cancer out, and these tests are not a screening test for it. They answer a different question from the scan, which is how much filtering reserve you have before treatment starts.
How often will my kidney function be checked during treatment?
More often than before it, and the interval depends on what you are having. Around surgery, creatinine is repeated in the days afterwards and again at follow-up. On systemic treatment, bloods are taken before each cycle, because the immunotherapy and targeted drug classes used in kidney cancer can affect the kidneys, blood pressure and thyroid, and doses or schedules are adjusted on those results. If a small tumour is being monitored rather than treated, function is checked alongside the follow-up scans. Ask for your own numbers each time and keep them, because a trend across months tells you far more than any single reading. This monitoring is delivered in-house at CION.
This page is general health information about kidney function tests, including creatinine and eGFR, in the setting of kidney cancer. It is not a diagnosis and it cannot replace a specialist review of your own results. Only a doctor who has seen your bloods, your urine result, your scans, your medicines and you can say what your numbers mean and what should happen next. If your function has fallen, or you are passing much less urine, feeling drowsy or breathless, or have visible blood in your urine, contact your team promptly rather than waiting for the next appointment.