Kidney numbers show up on many routine lab reports, often with a flag and little explanation. Early kidney disease usually causes no symptoms, so these tests are how most people first learn anything about their kidneys. This guide walks through the three results you are most likely to see.

It is general information. Your own results need to be read alongside your history, your medicines and earlier tests, by your own doctor.

Why kidney labs matter

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) notes that early kidney disease usually has no symptoms and that testing is the only way to know how well the kidneys are working. NIDDK recommends checking for kidney disease in people with diabetes, high blood pressure, heart disease or a family history of kidney failure, and yearly testing for people with diabetes.

Doctors use two main tests: a blood test that estimates filtering (eGFR) and a urine test for albumin (UACR). Each tells you something the other does not.

Creatinine: the starting number

Creatinine is a waste product from the normal breakdown of muscle, and healthy kidneys remove it from the blood. NIDDK explains that as kidney disease worsens, creatinine in the blood goes up.

Creatinine on its own can mislead. The National Kidney Foundation notes that besides kidney disease, creatinine can be affected by diet, muscle size, malnutrition and other chronic illness. A very muscular person and a frail person can have the same kidney function and different creatinine levels. That is why labs convert it into an estimate.

eGFR: an estimate of filtering

GFR stands for glomerular filtration rate, a measure of how much blood the kidneys filter. Labs estimate it (eGFR) from blood creatinine using a standard equation. NKF notes that some estimates also use cystatin C, another blood marker, which can help when creatinine alone may be misleading.

NKF describes the ranges this way:

  • 90 or higher: in the normal range
  • 60 to 89: may mean early-stage kidney disease
  • 15 to 59: may mean kidney disease
  • Below 15: may mean kidney failure

NIDDK frames it slightly differently: an eGFR of 60 or more is in the normal range, less than 60 may mean kidney disease, and 15 or less is called kidney failure. Both agree on the key point, which is that a single reading is a snapshot. NKF suggests repeating a low eGFR in about three months to see whether it stays low. NIDDK adds that you cannot raise your GFR, but you can work to keep it from going lower.

UACR: the urine test that is easy to skip

Albumin is a protein that belongs in the blood. Healthy kidneys keep it there; damaged kidneys let some leak into the urine. The urine albumin-to-creatinine ratio (UACR) measures this from a single urine sample.

According to NKF, a UACR below 30 mg/g is considered normal, or at goal, and a value of 30 or higher suggests albuminuria. NKF notes that a confirmed result of 30 or higher can point to kidney disease even when eGFR is above 60, and that results of 300 mg/g or higher are considered severely increased. Because results vary, the test often needs to be repeated before decisions are made.

UACR matters beyond the kidneys. NKF links higher albumin levels to higher risk of kidney failure and of heart attack, stroke and heart failure. That is one reason people with diabetes or high blood pressure are often asked for both tests, not just a blood draw.

Reading results over time

NIDDK suggests tracking results over time. A treatment plan is generally working when eGFR holds steady and urine albumin stays the same or goes down. Keep copies of your reports, or ask for them; HHS explains your right to access your own records.

Blood pressure is closely tied to kidney health. NIDDK calls controlling blood pressure the most important step in treating kidney disease, and it warns that NSAID pain relievers such as ibuprofen and naproxen can harm the kidneys. Our guide to checking blood pressure at home is a practical place to start.

Dr. Shtern is board-certified in Internal Medicine and Nephrology. Our article on why it helps when your internist is also a nephrologist explains how that overlap works day to day, and kidney care describes the practice’s approach. At Legacy Medical, labs are drawn in the office.

If you have kidney results you would like to understand better, the first visit is a complimentary meet and greet with Dr. Shtern. Bring your recent reports along.

This article is general information, not advice for your situation. Members can call the office with questions about their own care.