Serum (blood) creatinine
Creatinineis a waste product in your blood that comes from the digestion of protein in your food and the normal breakdown of muscle tissue. It is removed from your body through the kidneys. If you have kidney disease, the kidneys can have trouble removing creatinine from your blood. So, the level of creatinine in your blood starts to go up. High creatinine levels can be a sign ofacute kidney injuryand/orchronic kidney disease. A “normal” creatinine level in the blood is hard to define because it can change depending on your age, sex, body size, and other factors.
Cystatin C
Cystatin C is a protein that is produced by the cells in your body. Like creatinine, it is also removed from the body through the kidneys. If you have kidney disease, the kidneys can have trouble removing cystatin C from your blood. So, the level of cystatin C in your blood starts to go up. For some people, this blood test can be helpful to measure instead of (or in addition to) your serum creatinine to check your kidney health. This test is not as common as the creatinine test and can be more expensive.
Estimated glomerular filtration rate (eGFR)
The estimated glomerular filtration rate (eGFR) is an estimate of how well your kidneys are removing waste products from the blood. It is calculated using your serum (blood) creatinine level, age, and sex. It can also be calculated using your cystatin C level instead of, or in addition to, your serum (blood) creatinine level. A “normal” eGFR varies according to age – it naturally decreases as you get older. For this test, a higher number is better.
If you have chronic kidney disease (CKD), the eGFR is used to determine your CKD stage. In general, an eGFR value lower than 60 is a sign that the kidneys may not be working properly. An eGFR lower than 15 is a marker of kidney failure.
Measured glomerular filtration rate (mGFR)
In less common situations where a more accurate measure of your kidney function is needed, your healthcare provider may order a measured glomerular filtration rate (mGFR). The mGFR is a direct measure of how well your kidneys are removing waste products from the blood. It can be a complicated and lengthy process. So, it is not used as often as the estimated GFR (eGFR).
Your healthcare professional may recommend this test if a more accurate measure of your kidney function is needed. There are many ways to complete this test – some involve collecting all the urine you make in 24 hours; others involve multiple blood samples taken from your arm over several hours. The mGFR is sometimes called a different name - measured creatinine clearance (mCrCl).
Blood urea nitrogen (BUN)
Urea nitrogen is a waste product in your blood that comes from the breakdown of protein in the foods you eat. It is removed from the body through the kidneys. A “normal” BUN level varies, and usually increases as you get older. Checking your BUN level is usually not very helpful by itself. So, your healthcare provider will likely compare your BUN level to your creatinine and eGFR levels when evaluating your kidney health.
Urine albumin-creatinine ratio (uACR)
The urine albumin-creatinine ratio (uACR) test measures the amount of two different substances in your urine (pee) – albumin (protein) and creatinine. Healthy kidneys keep the albumin in your blood while filtering the creatinine out into the urine. So, this test checks to see how well your kidneys are keeping albumin in your body and sending creatinine out.
The uACR is calculated by comparing the amount of albumin in your urine with the amount of creatinine in your urine to find the ratio. A “normal” uACR level is less than 30 mg/g. For this test, a lower number is better. A uACR level of 30 mg/g or more can be a sign of albuminuria.
When you check the results from this test on your lab report, you may see many different numbers. Focus on the result that has the word ratio in the name. For example, the name on your report may be “alb/creat ratio”, “albumin/creat ratio”, or “albumin/creat ratio, random urine”.
Urine protein-creatinine ratio (uPCR)
This test is very similar to the uACR test described above. But instead of measuring only the amount of albumin in your urine (pee), it measures all the different proteins that may be present. In some forms of kidney disease (like IgA nephropathy, lupus nephritis, or glomerulonephritis) or when testing children for protein in their urine, your healthcare professional may choose to measure your uPCR instead of uACR. A “normal” uPCR level is less than 150 mg/g. For this test, a lower number is better. A uPCR level of 150 mg/g or more can be a sign of proteinuria.
