Ureterolithiasis (nephrolithiasis or kidney stones) is a disease affecting the urinary tract. Kidney stones occur due to buildup of certain salts and minerals that form crystals, which in turn stick together and enlarge to form a hard mass in the kidneys.
The stones move into the urinary tract and can cause blood in the urine, considerable pain and blockages in the urinary system.
Metabolic testing of a kidney stone patient’s urine to identify metabolites such as minerals and solutes that cause stones to form is key for preventing future ones. This testing is currently done by requiring the patient to collect their urine over a 24-hour period in a large container. The container is then sent to a laboratory for analysis and the results normally come back in 7 to 10 days.
Scientists from the Pennsylvania State University (University Park, PA, USA) and their colleagues developed SLIPS-LAB (Slippery Liquid-Infused Porous Surface Laboratory), a droplet-based bioanalysis system, for rapid measurement of urinary stone–associated analytes. The ultra-repellent and antifouling properties of SLIPS, which is a biologically inspired surface technology, allow autonomous liquid handling and manipulation of physiological samples without complicated sample preparation procedures and supporting equipment.
The team used enzymatic and colorimetric assay kits to measure metabolic profiles in urine. The uric acid assay was obtained from BioAssay Systems (Hayward CA, USA). Calibration experiments were performed using SLIPS-LAB and a FlexStation 3 microplate reader (Molecular Devices, San Jose, CA, USA). The performance of SLIPS-LAB for a spot urine test was compared with manual procedures in 96-well plates. A validation study was performed using SLIPS-LAB for detecting urine samples from patients with urinary stones.
The six-plex SLIPS-LAB device was designed for metabolic evaluation of urinary stone disease. The device conducts colorimetric and enzymatic assays in parallel for detecting calcium, citrate, uric acid, oxalate, and pH, which are among the most clinically relevant urinary analytes to assess stone risk and treatment response. The urinary stone–associated analytes of 24-hour urine samples from 15 individuals were examined using SLIPS-LAB. To study the metabolic profiles, the data were normalized to typical physiological values of 24-hour urine.
The test results can then be read using a scanner or a cell phone, and the scanned image can then be analyzed using a computer algorithm. All these steps, according to the authors, would take approximately 30 minutes in a physician’s office. An added benefit, they said, is that SLIPS-LAB is more cost-effective than regular, 24-hour testing.
Pak Kin Wong, PhD, professor of biomedical engineering and the principal investigator of the study, said, “We demonstrated that SLIPS-LAB enables the reagent and sample to move themselves and perform the reactions for us. It means the technology doesn’t require a technician to run any test machinery, so it is possible to do the test in non-traditional settings, like a physician’s office or even the patient’s home.”
The authors concluded that SLIPS-LAB will allow detection in a timely and cost-efficient manner and provide actionable diagnostic information and personalized treatment suggestions to individuals with urinary stone disease. The study was published on May 22, 2020 in the journal Science Advances.