Advantages of Dried Urine Testing Compared to a 24-hour Urine Collection

Simple sample collection

The collection procedure is simple and can be completed at home. A laboratory-grade filter paper strip is saturated with urine either by dipping it into urine that has been collected in a cup, or by urinating directly onto the strip. It takes very little urine to saturate the strip – only about 2 mL – so it isn’t necessary to have a full bladder before collecting the sample. After saturating the strip, it is then taped to a towel rack or other object from which it can hang down to dry without the strip itself touching anything.

Convenience of shipping.

After at least 4 hours of drying, the sample is ready to be placed in the collection kit box and mailed back to ZRT Laboratory for analysis. No refrigeration is required and shipping costs are low since samples can be sent in the regular mail. This makes shipment to the laboratory more convenient and allows for shipments from anywhere in the world without preservation (frozen or ice packs). Liquid urine is subject to bacterial contamination, and must therefore be shipped refrigerated or frozen.

Sample stability

ZRT Laboratory runs long-term stability experiments under different environmental conditions for each ofthe analytes we test. Results of these experiments show that urine dried on filter paper can be left at room temperature for at least a month without compromising test results, and samples can be stored frozen indefinitely. This is an advantage over liquid urine samples, where analytical results may be compromised if there are delays in shipment and/or if the samples are not kept refrigerated or frozen.

Multiple collections

Urine can easily be collected at specific time points throughout the day allowing for evaluation of the circadian rhythms of hormones such as cortisol and melatonin. The specific time points required are convenient, avoiding the risk of missed collections.

Creatinine correction

Because urine varies in dilution depending on the time of day or the volume of liquid consumed, all dried urine samples are also tested for creatinine. Creatinine is a natural breakdown product of creatine phosphate in the muscle tissue which is produced at a fairly constant rate. The more dilute the urine, usually as a result of higher liquid intake, the lower the creatinine level. Using creatinine as a correction factor1 is a very reliable method except in cases of very poor kidney function. All results are therefore expressed in micrograms of the hormone per gram of creatinine, which is more accurate than reporting hormone levels per unit volume, or per 24 hours.

Testing Accuracy

Dried urine has proven to be accurate throughout a wide range of analyte concentrations. Dried urine samples are extracted and analyzed in the laboratory using highly accurate methods including liquid chromatography/tandem mass spectrometry (LC-MS/ MS; used for free cortisol, free cortisone, and MT6s), gas chromatography/tandem mass spectrometry (GC-MS/MS; used for steroid hormone metabolites following enzyme digestion and derivatization to increase sensitivity), inductively-coupled plasma mass spectrometry (ICP-MS; used for elements testing2,3)and a direct mercury analyzer for mercury testing. For elements testing, ZRT Laboratory uses external controls with certified analyte concentrations to ensure accuracy.

ZRT Laboratory has carried out extensive validation studies showing that the dried urine test shows an excellent correlation with standard 24-hour collections.