Most kidney disease is found by accident, in a blood test taken for something else, and explained in a sentence that leaves the person frightened of dialysis for no reason.

Two readings, and what the gap between them can honestly support

Put in two eGFR results from your own letters or patient record, with roughly how long apart they were. The tool works out the rate of change, compares it with the decline everybody has with age, and — the part that matters — says whether the difference is bigger than the test's own variability. Nothing is saved, nothing leaves the page, and this cannot diagnose anything.

What the number actually is

• eGFR is an estimate, and the “e” is doing real work. It is calculated from a creatinine blood level together with age, using a formula. It is not a measurement of how much your kidneys filter; it is a prediction of it, and predictions have error bars.
• The error bars are wide enough to matter. Repeat the same blood sample and the reported eGFR can differ by several points; between two visits, differences of ten to fifteen per cent are ordinary. That is why a single reading, or a small change, tells you much less than people assume.
• It is unreliable in specific situations. Very high or very low muscle mass, a limb amputated, an acute illness, dehydration, pregnancy, a big protein meal or creatine supplements all shift creatinine without the kidneys having changed.
• It falls with age in everybody. After about forty, a decline of roughly one point a year is the ordinary course of a healthy life. A figure of sixty at seventy-five means something different from sixty at thirty-five.
• A single low result is not chronic kidney disease. The definition requires the abnormality to persist for at least three months, precisely because dips during illness are common and usually recover. If nobody has repeated it, the honest position is that it is not yet known.
• The stages are useful shorthand and terrible news delivery. Being told “stage 3” sounds like three out of four, or like cancer staging. It is not: it is a band of a continuous number, most people in it are stable, and it exists to organise monitoring rather than to predict a fate.

The test that was probably not done

• Kidney disease is described by two numbers, not one. The blood test gives the filtering estimate; a urine test gives the albumin-to-creatinine ratio, which is protein leaking where it should not. Both are needed to know what a result means.
• The urine number predicts more than the blood number. For the risk of progression, and for the risk of a heart attack or stroke, protein in the urine carries more weight than the eGFR does. Two people with identical eGFRs and different urine results are in different situations.
• It is a single sample, often first thing in the morning, and it is cheap. There is no preparation and no needle. It is left out because it is a separate request rather than because anybody decided against it.
• “Trace protein” on a dipstick is not the test. The dipstick is a rough screen; the ACR is a number you can put in a record and compare next year. Ask for the number, not the impression.
• If the urine result is raised, one class of drug becomes clearly protective. ACE inhibitors and ARBs reduce protein leak and slow decline, and the newer SGLT2 inhibitors do the same — which is why the urine result changes treatment and not only classification.

What actually happens to most people

• The commonest outcome of an early result is nothing. Most people with a mildly reduced eGFR and no protein in the urine remain stable for the rest of their lives, and the result functions as a reason to control blood pressure rather than as a countdown.
• The main risk is the heart, not the dialysis unit. Reduced kidney function is a strong cardiovascular risk marker, and people with early kidney disease are considerably more likely to have a heart attack or stroke than to reach kidney failure. That reframes what to do about it: the blood pressure, the cholesterol and the smoking matter most.
• Progression, when it happens, is usually slow and visible. It is measured in points per year over years, which is exactly why the direction is worth tracking and why one frightening letter proves little.
• Even at the point where replacement therapy is discussed, there are choices. Haemodialysis, dialysis at home, a transplant including from a living donor, and conservative care without dialysis are all real paths with different trade-offs, planned over months rather than decided in a crisis.
• Kidney disease is usually silent until late. There is no symptom to reassure yourself with, which is the argument for the boring monitoring rather than for anxiety: the numbers are the only early information there is.

What genuinely slows it down

1. Blood pressure, treated properly and measured at home. This is the single biggest lever, it works at every stage, and the target is usually lower than people expect. Ask what your target is and whether you are at it.
2. An ACE inhibitor or ARB, especially with protein in the urine. These do more than lower pressure: they reduce protein leak and slow decline. This is where the urine test changes the prescription.
3. An SGLT2 inhibitor, now used for kidney protection whether or not somebody has diabetes. This is the most significant change in kidney care in a generation and it has not reached everybody who would benefit. It is a reasonable thing to ask about by name.
4. Glucose control if diabetic, and weight and smoking for everybody. Smoking accelerates kidney decline as reliably as it does everything else, and stopping is measurable in the numbers.
5. Not taking anti-inflammatory painkillers regularly. Ibuprofen and its relatives reduce blood flow through the kidney. Occasional use in a healthy person is one thing; a daily habit alongside blood-pressure tablets is another.
6. Knowing which drugs to pause when you are ill. A short written plan for vomiting, diarrhoea or fever — which tablets to stop for a day or two and when to restart — prevents a large share of the sudden drops that land people in hospital.

The drugs: the protective, the expected surprise, and the combination to know

• Starting an ACE inhibitor or ARB makes creatinine rise a little, and that is expected. A rise of up to about a quarter to a third, settling, is not damage — it is how the drug works. Not knowing this is a recognised reason people are taken off the very drug that was protecting them.
• Three common drugs together are a recognised risk. An ACE inhibitor or ARB, plus a diuretic, plus an anti-inflammatory painkiller, is a well-described combination for sudden kidney injury — especially during an illness with dehydration. Each is reasonable alone; the third one is usually the one bought over the counter.
• Sick-day guidance is specific and almost never explained. During vomiting, diarrhoea or a fever with poor fluid intake, several classes are commonly paused for a day or two. Ask for it in writing, for your own list, and ask when to restart — and never stop a long-term drug on your own without that plan.
• Metformin, some diabetes drugs and some antibiotics need dose adjustment at lower eGFR. That is a pharmacist's routine work and worth one deliberate conversation, especially if the number has changed since the prescriptions were written.
• Contrast for scans and some procedures deserves a mention. If your kidney function is reduced, say so when a scan with contrast is booked; there are precautions, and dehydration on the day is the avoidable part.
• Bring the whole list, including what you buy yourself. The over-the-counter half is the half that causes the kidney problems and the half nobody writes down.

When a number drops suddenly

• A sudden fall usually has a cause outside the kidney. Dehydration, a diarrhoeal illness, blood loss, a new drug, a scan with contrast, or a urinary blockage. Sudden changes are frequently reversible, which is the opposite of the chronic picture and needs a different response.
• The reasons to be seen the same day are passing much less urine than usual or none at all, breathlessness with swelling, confusion, vomiting that stops you keeping fluids down, or a known low eGFR with a new severe illness.
• Not passing urine at all is an emergency, because a blockage can be relieved and the damage from leaving it is not always reversible.
• Blood in the urine, visible, needs investigating even once, and it is not a kidney-function question — it is a separate pathway that includes looking for other causes.
• After any sudden drop, the number needs rechecking once you are well. The recovered value is the one that belongs in your record, and it is routinely never taken — leaving somebody labelled with a stage they were only in for a fortnight.

The appointment, in six questions

Those six questions convert a letter with a number into a plan with a direction. If the appointment is short, the second and the fourth are the two that most often change what happens next.

What people are told, and what is so

The drill: 16 decisions

Sixteen ordinary moments — a letter with a stage on it, a number that fell during flu, a new tablet that pushed the creatinine up, a relative buying ibuprofen every day. Most have an instinctive answer that sounds sensible and is wrong. Pick your move; every answer explains why.

The card

Print it, write your own numbers in, and take it to the appointment.

🖨️ Print the card