What does diabetes do to the kidneys?

Each kidney holds about a million tiny blood-filtering units called glomeruli. These units make a fine distinction: they let waste and extra water through, keep useful protein in the blood. The membrane behind it works like a filter, thin even beside a strand of hair.

When sugar runs high for long, this order breaks down. Early on, many people’s filters work overtime; pressure inside rises and they strain blood faster than normal. The speedup looks harmless from outside, yet raises tension on the membrane. Over the years the membrane thickens, the cells around the filter wear out, and the filter’s old selectivity fades.

When the membrane starts leaking, the first protein into the urine is albumin. At first the amount is so small an ordinary urine test misses it. This picture is called microalbuminuria; current kidney guidelines call the same thing moderately increased albuminuria. A small sample of your first morning urine is enough.

The second measure is the filtering rate itself. The lab combines the creatinine level in a tube of blood from your arm with age and sex to calculate eGFR. The leading e means “estimated,” because no device measures the filtering rate directly.

Weaker filtering has one more consequence touching daily life. Insulin in the blood and some diabetes medications the kidney clears leave more slowly than before, so their effects last longer than expected. The kidney-side change therefore also raises the risk of low blood sugar. “Why does blood sugar drop?” gathers the reasons.

Why do these two measurements gain meaning together? Because damage doesn’t follow the same order in everyone: in some, filtering power drops without albumin in the urine rising at all. Looking at only one misses that person’s change entirely. One high result isn’t enough either; fever, a urinary tract infection, or recent hard exercise can raise albumin temporarily. Not one result, but several together, carry the meaning.

Blood pressure’s weight here is its own heading. Because the filter units are pressure-sensitive, high blood pressure pulls the already raised internal pressure higher still. Sugar and blood pressure load two separate burdens onto the same vascular bed. That’s also why the arm cuff appears so often in kidney monitoring.

For a long time diabetic nephropathy gives no complaint at all: no pain, no change in the urine’s look, no tiredness of its own. So monitoring checks urine and blood at regular intervals, without waiting for one.

The advanced stage, though, has its own signs. Swelling in the ankles and eyelids, heavily foamy urine, falling appetite, and unexplained exhaustion belong to this group. These are signs not of the early period but of a picture well along. The meaning of the silence sits right here.

The course isn’t one-way, but the two directions don’t weigh the same. In a study following people with type 2 diabetes for years, albumin that rose early returned to normal in one group. Still, in the whole group, progression outweighed reversal (Qiao et al., 2025). A change noticed early has a course to follow; that’s where measuring’s value sits.