NIST develops urine standard for kidney disease diagnosis

In order for doctors to diagnose kidney disease and other conditions that affect kidney function, such as diabetes and urinary tract infections, they will need accurate measurements of key compounds in urine. Now, thanks to a new standard reference material (SRM) from the US National Institute of Standards and Technology (NIST), those measurements are set to become more accurate and precise.

To check the health of your kidneys, clinicians look at the ratio of albumin to creatinine. Albumin is a protein created in the liver and creatinine is a small molecule and waste product that is filtered by your kidneys out of the body through your urine.

Albumin circulates through the bloodstream and helps keep fluid from leaking out from your blood vessels. It also transports other compounds, such as hormones and vitamins, throughout the body. Since the primary function of kidneys is to filter blood, small amounts of albumin can be expected in the urine. But when high levels of these compounds are detected in urine, this could mean your kidneys aren’t functioning properly.

Standards already exist to support measurements of creatinine; however, the standard for albumin has up until now been based in serum, a clear liquid component of blood, and not human urine. This increases the risk of inconsistent measurements from one lab to the next.

“The ideal standard is always in the same material as the clinical sample,” said NIST chemist Ashley Beasley Green. “If you send a urine sample to a lab, you expect the quality control material to be the same.

“It’s hard to determine the risk of kidney disease with inconsistent test results.”

The new SRM, dubbed SRM 3666, consists of four vials of different levels of albumin and creatinine. The four levels represent the clinical ranges of albumin in urine, from normal levels to those indicating disease. To develop the material, Green collaborated with the global clinical community to obtain urine samples from patients with kidney function that ranged from normal to having pre-existing disease.

The SRM comes with a data sheet that gives accurate measures of how much albumin and creatinine are in each vial. Laboratories that test urine samples can therefore use the SRM for quality control; researchers can run the material through their instruments, and if their results match the numbers on the data sheet, they can have greater assurance their instruments are working correctly. In addition to improving the accuracy of clinical measurements, the SMR could also have future impacts on clinical guidelines and improving the framework of how doctors diagnose and treat patients.

“This SRM directly impacts the health of individuals and the quality of care they receive,” Green said.

This work is part of a larger program, called the Urine Albumin Standardization Program, that has been active for over a decade to build these reference materials. International studies will now be conducted to further confirm that the material meets the needs of the entire community, from clinical labs to assay manufacturers. In the meantime, SRM 3666 (Albumin and Creatinine in Frozen Human Urine) is now available for purchase from the NIST Store.

Image caption: NIST bioanalytical chemist Ashley Beasley Green leads the urine albumin standardisation program and developed the standard reference material for albumin in human urine. Image credit: M DeLorme.