Understanding Kidney Disease: A Beginner's Guide

Being told your kidneys are failing is a great deal to take in at once, and most people leave that first appointment remembering only half of it. This guide covers the same ground more slowly: what your kidneys were doing for you, what chronic kidney disease is, and what the numbers on your laboratory results actually describe.

What healthy kidneys do each day

You have two kidneys, each roughly the size of your fist, sitting just below your rib cage on either side of your spine. Their main job is to filter your blood — removing waste and extra fluid, which leave your body as urine.

That filtering is not their only work. Kidneys also do several things that only become obvious once they stop:

• Keep the balance of water, salt, potassium and other minerals in your blood steady
• Help control your blood pressure
• Signal your body to make red blood cells, which is why anemia is common in kidney failure
• Help keep your bones healthy by managing calcium and phosphorus

Chronic kidney disease means the kidneys have been damaged, or have a problem with their structure, so they no longer filter blood the way they should. It usually develops gradually over years. Once it is advanced it generally cannot be reversed, which is why the aim of treatment is to slow it down and to replace the filtering work when there is no longer enough of it left.

Diabetes and high blood pressure are the most common causes. Heart and blood vessel disease, a family history of kidney disease, and older age all raise the risk as well.

How chronic kidney disease is staged

Kidney disease is described in five stages, set by a measure called eGFR — an estimate of how much blood your kidneys filter each minute. A higher number means more remaining function. The National Kidney Foundation sets the boundaries as follows.

• Stage G1 — eGFR 90 or higher, with signs of kidney damage present for at least three months
• Stage G2 — eGFR 60 to 89, with damage present for at least three months
• Stage G3a — eGFR 45 to 59, mild to moderate loss of function
• Stage G3b — eGFR 30 to 44, moderate to severe loss of function
• Stage G4 — eGFR 15 to 29, severe loss of function
• Stage G5 — eGFR below 15, kidney failure

Stage 5 is the point at which most people need dialysis or a transplant, and it is the stage most patients starting at a dialysis center have reached. The stage is not a countdown. Two people at the same stage can be in very different health, and how quickly someone moves between stages varies a great deal.

One thing surprises almost everyone: through the early stages, most people feel completely well. Symptoms such as loss of appetite, nausea, fatigue, trouble concentrating, itching, muscle cramps, foamy urine or a change in how often you pass urine tend to appear only once the disease is advanced. This is why kidney disease is so often found late, and why testing matters more than waiting to feel unwell.

The tests your doctor uses to track it

Two tests do most of the work, and you will see both repeatedly.

1. A blood test for GFR. Your blood is checked for creatinine, a waste product your muscles produce, and that figure is used to estimate your filtering rate. A GFR of 60 or above is in the normal range. Below 60 may mean kidney disease. A GFR of 15 or less is called kidney failure, and most people below that level need dialysis or a transplant.
2. A urine test for albumin. Albumin is a protein that passes into the urine when the kidneys are damaged, so it can show damage before filtering rate drops. The result is usually given as a ratio: 30 mg/g or less is normal, and more than 30 mg/g may be a sign of kidney disease.

Once you are on dialysis, other numbers join them — potassium, phosphorus, calcium, hemoglobin, and a measure of how well each session is clearing your blood. Your care team will explain which of yours they are watching most closely.

It is worth keeping your own copies of your results. A single reading matters far less than the direction it has been moving over months, and having the sequence with you makes any conversation with a new doctor faster.

If any of this does not match what your own nephrologist has told you, follow your nephrologist — they are working from your full history and your actual results. Bring this guide to your next session and ask about the parts that were unclear. The staff at your center would far rather answer a question early than have you worry about it for a month.