Most of you must have heard of foamy urine, urine that forms foam as if you are peeing in soapy water. If you see this, there is a cause for alarm, for this foam suggests the presence of excess protein in the urine.
Last week, we learned about kidney function tests, which give us an idea of where we stand on the spectrum of kidney disease-from normal kidney function (eGFR 90 or above) to completely lost function (eGFR 5 or below). Though eGFR suggests your location on the disease spectrum, it doesn’t tell anything about the trajectory of decline in kidney function.
For this purpose, urine protein serves as the best indicator. Urine protein not only tells us about kidneys’ health at any given time, as creatinine does, but also predicts the rate of kidney function decline.
Normal urine should not have any proteins. A human kidney consists of about a million microscopic filtration units called nephrons. Each nephron starts as a cup-like structure that contains a tuft of small blood vessels, and from the base of this cup extends a tube that connects with other bigger tubes. Nephrons make urine. When blood passes through this knot of blood vessels, it filters out all the waste products and comes out of the other side as washed out, and the waste products travel down the tubules as urine. This filtration process is highly selective, not allowing proteins to be leaked. Therefore, when the kidney starts leaking protein in the urine, it almost always suggests kidney damage.
How do we check protein in the urine?
Two main methods are used to check protein in your urine.
Urine Dipstick
A quick and inexpensive way to check for protein in the urine is the dipstick method. As the name explains, the dipstick test involves a calibrated strip that is dipped in the urine, and a change in the strip’s colour indicates protein in the urine. Keep in mind that dipstick is only a crude method. Consequently, it reports the protein as 1+, 2+, or 3+. For example, if your test report reads 1+ protein, you have a mild increase in urine protein. If the score is 2+ or more, it suggests a large amount of protein in the urine.
You can better manage your kidney disease by better understanding the importance of protein in the urine.
Despite this crudity, the dipstick is a good screening test. To confirm the presence of proteins and quantify their amount, your doctor may ask you to give a urine sample to calculate the exact amount of protein. This brings us to the more specific tests for calculating protein.
24-Hour urine protein and Albumin/Creatinine ratio
Many patients need clarification about the 24-hour urine protein and Albumin/Creatinine ratio. Let me explain.
A 24-hour urine protein is an ideal way to calculate the amount of protein in the urine. For this test, a patient collects his urine sample over a twenty-four-hour period in the following manner. He wakes up and discards his first pee; after that, he collects his urine in a container for the next twenty-four hours, including his first urine the following day. This collection is much easier said than done. Consequently, such 24-hour urine samples used to be full of errors and nuisance.
To make this test more convenient for the patient, researchers came up with the Albumin/Creatinine ratio. You only need a random urine sample for this test, preferably the early morning one. The lab calculates the Albumin and Creatinine from this sample, and their ratio is then measured. The number achieved by this ratio corresponds to the total amount of protein obtained by a 24-hour urine sample of the same patient. In short, Albumin/Creatinine ratio closely estimates your twenty-four-hour urine albumin excretion.
Are Albumin and Protein in the urine two different things?
These terms also confuse patients. Proteinuria means all types of protein in the urine. Albuminuria means only Albumin. However, remember that Albumin is the main protein in the urine, and all diseases that make kidneys leaky to proteins result in Albuminuria, except one condition called Multiple Myeloma. In other words, whether you check Albumin or protein in the urine, it almost always means Albumin.
Note: For this very reason, the dipstick is designed to detect only Albumin in the urine, not other proteins.
How to read your report
Labs report urine protein in three main groups: Below 30, 30 to 300, and more than 300. If urine protein is under 30, you have normal protein in the urine. If it is between 30 and 300, you have mildly increased protein in the urine. This needs to be looked at and managed accordingly. Finally, if you have a protein of more than 300, you have significant proteinuria.
Once your treatment starts, this same test serves as a marker to see improvement in proteinuria. A decline in the amount of protein in the urine indicates improvement in your kidney health.
Simply put, proteinuria holds the key to both your kidney function assessment as well as its prognosis. You can better manage your kidney disease by better understanding the importance of protein in the urine.
The writer is an Internist and Nephrologist. He has won Top Internist Award in 2021 and Top Nephrologist Award in 2022 from Michigan, USA. He can be reached on Twitter @awaiszaka.