urinary albumin creatinine ratio in dried microsamples

An article by Tasso Miliotis et al at Astra Zeneca Sweden and three other Swedish institutions was published in the March 2024 edition of the Journal of Applied Laboratory Medicine. Their article describes the use of two microsampling devices, including the Mitra^® device with VAMS^® technology, for measurement of urinary albumin creatine ratio (UACR). The paper is entitled, “Patient-Centric Quantitative Microsampling for Accurate Determination of Urine Albumin to Creatinine Ratio (UACR) in a Clinical Setting.”  

The study showed that excellent analytical and clinical correlation was observed between standard wet urine analysis conducted on a clinical chemical analyzer and a de novo LC-MS/MS for analysis of dried urine extracts.

In their study paper, the authors concluded that both sampling devices used would be amenable for remote sampling, which has the potential to transform the way clinical research is conducted by significantly reducing the frequency of clinic visits and thereby reducing the sampling burden for patients.”

Chronic Kidney Disease 

Chronic kidney disease (CKD) has a devastating effect on individual health and health systems. It was reported that in 2017, approximately 1 in 10 people globally (843.6 million) were suffering from kidney disease. Further, kidney disease has moved up list of causes of global fatalities, from 19th position in 2013 to 12th position in 2017. CKD is predicted to be the fifth most prevalent cause of death by 2040.

Measuring Kidney Function

Our kidneys play a vital role in filtering waste and excess water from our blood to create urine. There are a several tests which measure this filtration process and kidney function.

A common test is called eGFR, which stands for estimated glomerular filtration rate. The eGFR test measures the rate at which serum creatinine (a breakdown product of protein) is processing in your kidneys, and the test is adjusted for age, size, gender. As the rate of filtration drops, the eGFR indicates impaired kidney function brought on by disease.

Measuring Urinary Creatinine Albumin Ratio (UACR) 

A standard test to measure kidney impairment (damage) is based on measuring urinary creatinine albumin ratio (UACR).  

Kidneys are essential for maintaining osmotic balance in the body by reabsorbing water to help maintain hydration, they also function to filter out certain waste products (such as creatinine). As kidneys begin to fail, they reduce their ability to filter. This impacts on the health of other organs, such as the heart, eventually leading to organ failure and death.   

To understand the degree to which kidneys fail, the urinary creatinine albumin ratio (UACR) is employed. As kidneys fail, they become more porous and begin to allow protein (and other substances) to enter the urine from the blood. As a result, a ratio of human serum albumin (HSA – the most abundant protein in blood) and creatinine (a natural component of urine) is calculated. Normal values for men are reported to be 17 mg/g and for women, 25 mg/g. Values above these indicate microalbuminuria which, if left unchecked, can lead to full albuminuria with values over 299 mg of albumin per g of creatinine.

Early Detection of Kidney Disease 

As with many other conditions, catching the early signs of kidney disease allows for more efficacious interventions. However, with chronic kidney disease (CKD), a serious and progressive reduction in renal performance is often silent as it evolves. As many as 1 in 10 people with CKD are unaware that they are developing the potentially fatal condition.  

For this reason, Tasso Miliotis et al suggested that using precise UACR measurements of urine microsamples collected among patients at home would be an effective tool for early detection and intervention. Remote urine sampling would help increase the frequency of sample collection compared to onsite urine testing at clinical sites. More frequent and convenient sampling would be valuable for early diagnosis and vital for regular monitoring and intervention with therapy. Moreover, a higher rate of sample collection would also be highly beneficial for CKD drug development.

A Patient-Centric Sampling (PCS) Approach to UACR

As with all wet biofluids, the handling of urine samples can be messy, inconvenient, unstable at room temperature over time, and hazardous. Moreover, transportation of liquid human biofluids is strictly regulated. Overcoming these challenges inspired the research team to embark upon a study to develop a dried urine assay from two microsampling devices: Mitra^® and Capitainer^®.  It was hoped that the benefits of using volumetrically collected dried urine samples would overcome the challenges and limitations of liquid sampling, as highlighted above in the discussion of wet urine samples.

Study Methods and Findings 

An LC-MS/MS method was developed for both Albumin and Creatinine on urine extracts from dried microsamples, using the Mitra and Capitainer devices. 

• Within batch precision (%CV): 
  • Mitra = 2.8% and 4.6%
  • Capitainer = 4.0% and 8.6%

• Between batch precision (%CV):
  • Mitra = 5.3% and 6.1%
  • Capitainer = 6.7% and 9.0%

• Storage at room temperature for both devices changed from 98% to 103% over three weeks.
  
  
• Freeze thaw stability was also good where both devices showed stability over three cycles.
  
  
• Both devices fulfilled acceptance criteria for recovery
  • Mitra = 104 (SD 7.0%)
  • Capitainer = 95 (SD 10.0%) 

• Both devices fulfilled acceptance criteria for accuracy when testing the urine of 32 UACR patients. 
  • Mitra = 102 (SD 8.0%) 
  • Capitainer = 95 (SD 7.4%) 

Study Authors' Discussion

LC-MS UACR measurement on both microsampling devices showed “excellent accuracy and precision compared to a clinical chemistry analyzer using neat urine.” This patient-centric approach brought advantages, such as stability of the samplers at room temperature, and inexpensive shipping without refrigeration since the samples were dry.  

This approach could help diagnose early onset of CKD from remotely collected samples. Both devices were used in a clinical study setting whereby collecting and testing samples from patients (n=32) was performed from a mobile collection clinic ‘Heart Bus.’  

One drawback is that LC-MS is expensive compared to the cost of processing samples on chemical analyzers. However, the research group are anticipating that the assay will eventually work on these analyzers too, even though low-volume samples (of 10- 20 µL) are not possible on current analyzers. Nevertheless, the assay could open access to remote UACR sample collection.

Neoteryx Comments

This is another excellent example of how microsampling can enable the democratization of remote personalized sample collection. The remote urine sampling approach utilized by the researchers in this study might also work for other high-risk patient populations, such as those with diabetes. It is hoped that this remote sampling approach will continue to lower the barrier of access to diagnosis, monitoring and early intervention of conditions such as CKD which are silent in the early stages.   

This study paper was summarized for our readers by James Rudge, PhD, Microsampling Technical Director, Neoteryx. This is curated content. To learn more about the important research outlined here, visit the original article published in the Journal of Applied Laboratory Medicine.  

For further reading on other research studies that leveraged remote microsampling, please visit our Microsampling Resource Library.

Image Credits: Trajan Scientific and Medical, iStock Photos