Kidney Function Tests Explained: GFR, Creatinine & Urine Albumin in Palm Beach County, FL

What it involves

Kidney function is checked with two simple tests: a blood test that estimates how well the kidneys filter, and a urine test that looks for a protein called albumin. Your provider reads them together, along with your blood pressure and blood sugar, and explains what the numbers mean for you. This page explains the terms so a lab report is less confusing when it arrives.

Who this is for

• Patients with diabetes, who NIDDK says should be tested for kidney disease every year
• Patients with high blood pressure or heart disease who have not had kidney tests recently
• Patients with a family history of kidney failure who want to know where they stand
• Patients who received a lab report with kidney numbers and want it explained in plain words

What to expect

• A review of your history, medicines, blood pressure, and any earlier kidney results
• A blood draw for creatinine and an estimated GFR, and a urine sample for albumin
• An explanation of each result and how it compares with the ranges NIDDK publishes
• A follow-up plan, including how often to repeat the tests

The two tests, in plain words

NIDDK says kidney disease is found with a blood test that measures glomerular filtration rate, or GFR, and a urine test that checks for albumin. GFR describes how well the kidneys filter waste from the blood. Albumin is a protein that should stay in the blood, so finding it in urine can be a sign of kidney damage. Creatinine and BUN also appear on a routine chemistry panel, and the basic metabolic panel explained page shows where those two kidney waste products sit next to glucose, calcium, and the electrolytes.

What creatinine tells your provider

Creatinine is a waste product made when muscle breaks down. Healthy kidneys remove it, so NIDDK explains that as kidney disease gets worse, the creatinine level in the blood goes up. Providers use that blood creatinine level to estimate your GFR. You will usually see creatinine on the same lab page as other routine blood results. Healthy kidneys also help convert vitamin D into the form the body can use, and the vitamin D and B12 blood tests guide explains why a low vitamin D result can lead a provider to look at kidney results.

How to read a GFR number

NIDDK describes the ranges this way:

• A GFR of 60 or higher is in the normal range
• A GFR below 60 may mean kidney disease
• A GFR of 15 or lower means kidney failure, and most people at that stage need dialysis or a transplant

How to read the urine albumin result

A urine test can be a quick dipstick, or a urine albumin-to-creatinine ratio, called UACR, which compares the albumin with the creatinine in the same sample. NIDDK says a normal result is 30 milligrams per gram or less, and a number above 30 may point to kidney disease. One result is a starting point. Your provider decides whether to repeat it. Albumin is only one line that can appear on a urine test, and the urinalysis guide explains the physical, microscopic, and chemical checks that can be done on a urine sample.

Who NIDDK says should be tested

NIDDK says you should be checked for kidney disease if you have diabetes, high blood pressure, heart disease, or a family history of kidney failure. People with diabetes should be tested every year, and others should ask their provider how often. This is the reason kidney results often come up during diabetes management visits and blood pressure visits. Because high blood pressure is one of the reasons to have kidney tests, the blood pressure readings explained guide shows how to measure it correctly and what the ranges mean. Kidney problems are one reason ankles and legs swell, and the leg swelling evaluation guide shows where these tests fit among the others a provider may use. NIAMS also lists chronic kidney disease among the conditions that can raise uric acid and the risk of gout, and the gout evaluation explains how kidney health and joint flares are connected. Kidney failure is one of the medical causes MedlinePlus lists for muscle cramps, as the muscle cramps guide explains.

Before you go in for blood work

Ask the office whether your tests need fasting, since not every test does. If fasting applies, the fasting blood work preparation guide covers what to drink and what to skip. Bring a list of your medicines and the date of any earlier kidney tests. Liver enzymes are often drawn on the same visit as kidney tests, and the liver function tests explained page describes ALT, AST, and bilirubin in the same plain terms. Dehydration from a stomach illness can change kidney blood tests, and MedlinePlus says providers may check kidney function when dehydration is suspected, as the stomach flu and dehydration guide describes.

Sources

• NIDDK — Tests & Diagnosis for Chronic Kidney Disease