In this article, we overview the possibilities for dried urine testing as an alternative to standard liquid urine testing, with a particular focus on patient convenience, sample stability, and accuracy.

But first, what is dried urine testing? This is a simple and discrete collection method that requires the individual being tested to saturate a filter card with urine. Depending on the analyte being tested, this will either involve collection of a single sample or up to four separate samples over a 24-hour period. The samples are then dried and sent directly into a testing lab.

The benefits of dried urine sampling

• Dried urine does not support microbial growth and is thus considered safe and suitable for regular shipment and storage. This is in contrast to liquid urine samples, which must be treated as biohazardous material at all times. This eliminates the need for sample refrigeration and expensive cold chain logistics.
• Crucially, dried urine samples are highly stable which further removes the need for special measures to preserve stability when handling liquid urine.
• Dried urine sampling is ideal for at-home testing, which spares the individual the burden of travelling to a healthcare facility, especially if repeat sampling is required.
• Because dried samples involve much smaller volumes than liquid samples and do not require refrigeration, this approach also eliminates the hassle and risk of storing cups of liquid urine at home in one’s fridge when that approach is chosen.
• It has been suggested that the increased convenience afforded by dried urine testing may improve patient adherence (1).

Dried urine samples offer accuracy in analysis

Although dried urine testing is not mainstream in clinical laboratories, interest in the method is growing and numerous scientific studies have demonstrated excellent correlations between fresh and dried urine samples for the measurement of a range of analytes.

For instance, Newman et al. have demonstrated through multiple studies that dried urine leads to equivalent measures as liquid urine for steroid hormones including cortisol, cortisone, and several cortisol metabolites, as well as the reproductive hormones estrone, oestradiol, ⍺-pregnanediol, and β-pregnanediol (2,3).

A study carried out at the French National Institute of Health and Medical Research (Inserm) to detect four inherited metabolic disorders found that urine samples dried on filter paper were highly stable even after 7 days at room temperature, and that the measurement of target amino acids and organic acids correlated extremely well with that of fresh urine from the same patients (4).

The impact of dried urine samples in the metabolic disease field is highlighted by the fact that the newborn screening programme in Quebec includes at-home collection of urine specimens from 21-day-old babies, which are dried on filter paper and sent to testing labs. Although voluntary, this programme has a very high compliance rate of approximately 90 %, with more than 3.5 million babies screened this way since 1973. Importantly, this method is able to detect at least one disease that is not picked up in the standard blood-based newborn screening programmes (5).

What are the potential applications for dried urine testing?

In principle, many applications that use liquid urine could be adapted for dried urine samples. In the following sections, we look at some of the major applications for urine testing and comment on the potential impact of dried urine testing for each one.

Kidney and liver function testing.  Urinalysis to monitor kidney and liver health usually involves a combination of visual, microscopic and chemical tests to determine the physical and biochemical properties of urine and to measure certain metabolites that can provide information about disease risk and severity. Cloudy urine can indicate an infection or kidney problems, while very dark-coloured urine that smells of ammonia can be a sign of liver failure. With regards to metabolites, the urine albumin-creatinine ratio (uACR) test is widely performed in diabetes patients on an annual basis, to monitor their risk of developing kidney disease. The feasibility of performing the uACR test on dried urine has been demonstrated (7), and it is plausible that other relevant metabolites could be measured in dried urine format. This could have a major impact on certain patient groups, for example, diabetes patients who could avail of at-home sampling for uACR as well as at-home dried blood spot sampling HbA1c, a biomarker of long-term glucose control.

Steroid hormone testing. This includes analyses of steroid hormones and their by-products, often over multiple days or months, to shed light on hormone metabolism and identify hormone imbalances. Such tests may also be used to monitor the response to medication in an individual receiving treatment for a hormone disorder. Within conventional medicine, the majority of hormone tests are currently performed using liquid urine, and such tests are often critical in diagnosis, for, e.g., diabetes and cortisol disorders. Dried urine tests would lessen the burden on these patient groups to attend regular hospital appointments and would potentially improve patient compliance to treatment and follow-up.

Reproductive and women’s health. Hormone testing is widely used in this broad area of medicine, e.g., during the transition to menopause to guide/identify the need for hormone replacement therapy, and to identify the risk for certain oestrogen-dependent cancers. Additional uses included pregnancy testing, monitoring during pregnancy, e.g., for gestational diabetes and pre-eclampsia. At present, these tests are generally performed using liquid urine but the possibility to use dried urine samples collected at home would be very advantageous for healthcare systems and patients alike, by reducing the number of in-person appointments and lowering the risk of infection among vulnerable individuals.

Heavy metal and toxicity testing. Urine is a major exit route for heavy metals and other toxic elements that do not need to stay in the body, thus urine is often used to check for poisoning or exposure to heavy metals if suspicious symptoms are present. Such tests are routinely used to identify or rule out cases of arsenic, cadmium, mercury, lead and iodine poisoning. These tests require repeat samples taken over a 24-hour period, which can create storage challenges, especially when sampling at home. Dried urine testing can offer a simpler method with fewer sampling time-points without the hassle of collecting and refrigerating many cups of urine.

Drugs abuse testing. At-home urine sampling is currently used to test if one or more prescription or illegal drugs are present in urine. Such drugs include marijuana, cocaine, opiates, methamphetamine, amphetamines, PCP, benzodiazepine, barbiturates, methadone, tricyclic antidepressants, ecstasy, and oxycodone. These tests are qualitative, and any sample that yields a positive result should be sent to a lab for further analysis. According to the FDA, these at-home tests are fairly sensitive and will yield a preliminary (or presumptive) positive test result if drugs are present in the urine. In summary, urine is common matrix in drugs-of-abuse testing and a dried sampling format could provide many benefits.

Nutritional testing. Urine amino acid analysis can provide indications of overall health status and is useful in the identification of various health or nutritional disorders. Liquid urine collection, storage and cold transportation methods are inconvenient, carry the risk of sample leakage and are costly, which has motivated researchers to explore dried urine as a sample format for amino acid testing. A recent study that involved healthy volunteers demonstrated similar concentrations obtained in liquid urine and dried urine samples from 10 healthy individuals, indicating the potential of this approach for patient-centric urine testing for a range of applications (6).

Watch this space!

To sum up, the benefits of dried urine testing are clear and well-documented, and as sampling technologies evolve, we expect that more and more clinical laboratories will adopt dried urine testing in place of fresh urine testing where relevant. Stay tuned for more news about dried urine sampling!

References

1. Newman M, Curran DA. Reliability of a dried urine test for comprehensive assessment of urine hormones and metabolites. BMC Chem. 2021 Mar 15;15(1):18.
2. Newman M, Curran DA, Mayfield BP. Dried urine and salivary profiling for complete assessment of cortisol and cortisol metabolites. J Clin Transl Endocrinol. 2020 Nov 27; 22:100243.
3. Newman M, Pratt SM, Curran DA, Stanczyk FZ. Evaluating urinary estrogen and progesterone metabolites using dried filter paper samples and gas chromatography with tandem mass spectrometry (GC-MS/MS). BMC Chem. 2019 Feb 4;13(1):20.
4. Blasco H, Garrigue MA, De Vos A, Antar C, Labarthe F, Maillot F, Andres CR, Nadal-Desbarats L. Filter paper saturated by urine sample in metabolic disorders detection by proton magnetic resonance spectroscopy. Anal Bioanal Chem. 2010 Feb;396(3):1205-11.
5. Auray-Blais C, Boutin M, Lavoie P, Maranda B. Neonatal Urine Screening Program in the Province of Quebec: Technological Upgrade from Thin Layer Chromatography to Tandem Mass Spectrometry. Int J Neonatal Screen. 2021 Mar 20;7(1):18.
6. Meikopoulos T, Begou O, Gika H, Theodoridis G. Dried urine spot (DUS) applied for sampling prior to the accurate HILIC-MS/MS determination of 14 amino acids. Talanta. 2024 269:125489.
7. Löfgren L et al. Patient-Centric Quantitative Microsampling for Accurate Determination of Urine Albumin to Creatinine Ratio (UACR) in a Clinical Setting, The Journal of Applied Laboratory Medicine, Volume 9, Issue 2, March 2024, Pages 329–341.