The two kidney numbers on your bloodwork

Your results come back and there are two lines nobody mentioned. One says eGFR. The other says albumin to creatinine ratio, or ACR, and it came from the small container you were sent home with.

If either was flagged, the flag arrived without a sentence explaining it, and the appointment where you could ask is six weeks away.

Neither number is as alarming as an unexplained flag feels. They are two measurements of the same organ, and they are on your chart because kidneys are one of the places long standing high blood sugar and high blood pressure do quiet damage, years before anyone feels anything.

The two numbers, and what each is for

eGFR estimates how fast your kidneys are filtering. It is calculated from creatinine, a waste product from muscle that is measured in your blood, adjusted for your age and sex. Higher is better. When it drops, it means filtering has slowed.

ACR measures albumin, a protein, in your urine. Healthy kidneys keep protein in the blood where it belongs. When small amounts start appearing in urine, it is a sign the filters are leaking a little. Here, lower is better and a rise is the warning.

The two are checked together because either can move first. Someone can have a perfectly ordinary eGFR and a rising ACR, and that is the earliest useful signal there is. Testing only the blood misses it, which is why the urine container is not optional.

Diabetes Canada recommends kidney testing at least once a year for adults with type 2 diabetes, and more often if something is changing.

These are two measurements of the same organ, taken from different ends. Together they say more than either one does alone.

Why one odd result is not a diagnosis

Kidney numbers move around, and a single reading is a snapshot taken on a particular day.

An ACR can be raised temporarily by a urinary tract infection, a fever, hard exercise the day before, being on your period when you gave the sample, or very high blood sugar at the time. An eGFR can dip when you are dehydrated or have been vomiting, and it reads differently in people with a lot of muscle and in people with very little.

That is why kidney disease is not diagnosed from one result. The pattern has to hold across repeat tests over a few months. If one number is off, the usual next step is another test, not a conclusion.

What actually protects kidneys

The honest answer is unglamorous and it is mostly two things.

Blood pressure. Of everything on this list, blood pressure control does the most for kidneys over a decade, and it is silent enough to be easy to leave alone. A run of home readings brought to your team is the most useful thing most people can produce.

Blood sugar. The same story, over the same timescale. Nobody needs perfection here, and steady beats heroic.

After that: not smoking, which damages the small vessels kidneys are mostly made of, staying reasonably hydrated with water rather than with anything sweetened, salt, which matters mostly through blood pressure, and taking the medications your prescriber has put you on for exactly this reason.

What does not belong on the list is a protein restriction you designed yourself. Cutting protein hard is sometimes prescribed, is not a do it yourself intervention, and for many people with early changes is not recommended at all.

The medication part, which is where people get caught

Several common things interact with kidneys, and this is the part of the article to read twice.

Anti inflammatories. Ibuprofen, naproxen and diclofenac, including the ones you can buy without a prescription, reduce blood flow through the kidney. Taken occasionally by a healthy person, that is usually fine. The combination that causes real trouble is an anti inflammatory together with an ACE inhibitor such as ramipril or perindopril, or an ARB such as losartan or telmisartan, plus a diuretic, particularly during an illness with vomiting or diarrhea. Ask your pharmacist what to use for pain instead. It takes two minutes and this is a genuinely common cause of avoidable harm.

ACE inhibitors and ARBs. These often appear precisely because your ACR is rising, since they protect kidneys as well as lower blood pressure. Confusingly, a small rise in creatinine after starting or increasing one is expected, and your prescriber usually rechecks bloodwork shortly afterwards. A number moving on that recheck is not automatically a reason to stop, and stopping without telling anyone loses the protection.

SGLT2 inhibitors such as empagliflozin and dapagliflozin are now also used to protect kidneys. They increase urination, so they need care during dehydrating illnesses.

Metformin is dosed according to kidney function and is sometimes paused around scans that use contrast dye. Both of those are your prescriber’s calls, not yours.

None of that is a reason to change anything today. It is a reason to have everything you take, prescription and over the counter, checked against your kidney numbers once.

Worth a word with your care team

Message your team if your ACR has gone up on more than one test, if your eGFR has dropped noticeably from your usual, or if it has been over a year since either was done.

Call sooner for swelling in your ankles, feet or face, urine that is persistently foamy, blood in your urine, or a stretch where you are urinating much less than normal. Also call if you are into a second day of vomiting or diarrhea and you take a blood pressure medication, a diuretic or an SGLT2 inhibitor: dehydration and those medications together are hard on kidneys, and there is usually specific sick day advice worth having before you need it.

Go to emergency for breathlessness lying flat, sudden swelling with rapid weight gain, or confusion.

One small place to start

Find your last eGFR and ACR, from your results portal, your pharmacy, or by asking, and write both down with the date. Two numbers on a piece of paper.

If you are a 360Care member, send them to your care team in the app along with a photo of everything you take, including the painkillers in the cupboard. That is the whole review, and it is the one most people never get.