Abstract:
A composition and method for preserving a urine sample and a preservative delivery vessel are disclosed wherein treatment of the urine sample aids in preserving circulating cell-free nucleic acids in urine over a wide range of dilution ratios within temperature fluctuations that can occur during urine sample handling, storage and transportation. The urine sample preservation composition and method and preservative delivery vessel provide a method for obtaining high quality stabilized urinary cell-free nucleic acids for clinical diagnostics development and application.

Description:
TECHNICAL FIELD 
       [0001]    The present teachings relate to a urine preservative composition for stabilization of cell-free nucleic acid in a urine sample, a method for preserving a urine sample and a preservative delivery vessel. 
       BACKGROUND 
       [0002]    Detection of circulating cell-free DNA (cfDNA) in blood plasma derived from tumor, fetus and transplanted organs has been well documented. See U.S. Patent Applications 2014/0080112 and 2010/0184069 incorporated by reference herein. These circulating cfDNAs can pass from the blood through the kidney barrier into urine. The obvious advantages and non-invasive nature of urine sampling makes urine a useful source of fetal and tumor DNA for the development of noninvasive prenatal and cancer diagnostic and prognostic tests, in addition to detection and identification if other disease states. However, the inherent instability of cfDNA in urine hinders its clinical utility. Nucleated cells in urine can also release genomic nucleic acids into urine leading to an increased nucleic acid background during sample processing and storage. 
         [0003]    The discovery of cell-free nucleic acids in the circulation has opened up new opportunities for non-invasive diagnostic applications in cancer testing and prenatal diagnosis (Tong Y K and Lo Y M D. Diagnostic developments involving cell-free (circulating) nucleic acids.  Clinica Chimica Acta  2006; 363:187-196). Since the confirmation of cfDNA presence in urine, there has been much interest in the potential utility of urinary DNA for clinical diagnostic development. (Botezatu I, Serdyuk O, Potapova G, et al. Genetic analysis of DNA excreted in urine: a new approach for detecting specific genomic DNA sequences from cells dying in an organism.  Clinical Chemistry  2000; 46:1078-1084.) The main advantage of urine over other body fluids (e.g., blood) is that urine sampling is truly non-invasive and it can be obtained safely and in large amounts with very limited training. When employing urinary cfDNA, however, it is important to minimize release of cellular DNA from nucleated cells and stabilize cfDNA following urine collection since cfDNA targets are present at low quantities and degrade rapidly. (Su Y H, Wang M J, Aiamkitsumrit B, et al. Detection of a K-ras mutation in urine of patients with colorectal cancer.  Cancer Biomarkers  2005; 1; 177-182.) (Cannas A, Kalunga G, Green C, et al. Implications of Storing Urinary DNA from Different Populations for Molecular Analyses.  PLoS ONE  2009; 4: e6985). Urine conditions (i.e. pH, nuclease activity) are markedly different from those of blood. On average nuclease activity in fresh urine is greater than that in blood plasma. (Cherepanova A, Tamkovich S, Pyshnyi D, et al. Immunochemical assay for deoxyribonuclease activity in body fluids.  Journal of immunological methods.  2007 Aug. 31;325(1):96-103.) All articles are incorporated by reference herein. 
         [0004]    Effective stabilization of the nucleated blood cells in urine alone is not sufficient to effectively stabilize the native cell free DNA compliment in fresh urine. Inhibition of the significantly higher nuclease activity in urine as compared to blood plasma is critical to the effective stabilization. Therefore, requirements for effective stabilization of the native cell free DNA in urine samples are multi-fold. 
         [0005]    Effective stabilization of cell free-DNA in urine requires stabilization of nucleated blood cells in urine, quenching of damaging free formaldehyde that may be present from stabilizing/preserving agents and blocking of the high nuclease activity in urine. There is a need for nucleated blood cell stabilization to reduce the level of contaminating genomic DNA to the overall DNA yield. There is a need for a preserving/stabilizing agent which does not compromise or destroy the structural integrity of the actionable mutations in the cell free DNA and or ctDNA due to free formaldehyde. There is a need for blocking enzymatic active (i.e. DNase activity) in fresh urine to prevent the enzymatic activity that will rapidly hydrolyze nucleic acids. Thus, there is a need for a preservative reagent that can preserve the original proportion and integrity of cfDNA in urine post specimen collection. 
         [0006]    It is also necessary to address pre-analytical issues that arise during the time between urine collection and cfDNA isolation. These include delays in urine processing and specimen storage temperature. Such conditions may cause cellular DNA contamination and subsequently alter cfDNA levels circulating in urine. Thus, in order to obtain reproducible results, it is essential to standardize the pre-analytical procedure for urine sample handling. cfDNA preservation and stabilization in urine should be an integral part of the non-invasive diagnostic test development using urine as the source of genetic material. Thus, there is a need for a urine preservation method and preservation delivery vessel that can maintain the cfDNA concentration in urine post specimen collection. There is a need for a urine preservation method and preservation delivery vessel that offers the benefit of preserving urine cellular material that may later be processed and the nucleic acids isolated for molecular diagnostic analysis. 
       SUMMARY OF THE INVENTION 
       [0007]    The present teachings contemplate a urine preservative composition for stabilization of cell-free DNA in a urine sample. The present teachings provide for stabilization of nucleated blood cells in urine. The present teachings further provide for quenching substantially all available free formaldehyde that may be present from stabilizing/preserving agents which release formaldehyde. The present teachings provide for blocking of nuclease activity. Thus, the present teachings provide a preservative reagent that can preserve the original proportion and structural integrity of cfDNA in urine post specimen collection. 
         [0008]    The present teachings contemplate a method that can stabilize cfDNA in urine and minimize the post-sampling urinary DNA background for an extended period of time at various storage temperatures. This new methodology provides clinical laboratories with great flexibility and convenience in urine sample processing, handing and storage for urinary nucleic acid testing as it eliminates the necessity for immediate separation of supernatant after urine collection and refrigerating/freezing urine for transport. 
         [0009]    Such a method may comprise a step of dispensing into a specimen container a predetermined amount of a urine preservative by removing the urine preservative from a sealed vessel. The method may also include a step of contacting the urine preservative with a urine sample. The method may also include the step of sealing the specimen container with the urine sample and the urine preservative contained within it. The step may also include causing the sealed specimen container to be shipped to a clinical laboratory for analysis of the urine sample. The urine sample, upon being preserved, may be capable of analysis after a period at least  168  hours or at least  7  days has elapsed. 
         [0010]    There may be a urine collection step of obtaining a urine sample from a patient into a specimen container prior to the contacting step. The urine sample may be a random specimen, a first morning specimen, a midstream clean catch specimen, a timed collection specimen, a catheter collection specimen, or a suprapubic specimen. The urine sample may be preserved at the collection site, for example a doctor&#39;s office. The method may include a step of transporting the preserved urine sample to another site, for example a clinical laboratory at which analysis will occur. The clinical laboratory may perform urinalysis testing on the preserved urine sample and report the results. The preserved urine sample may be processed for isolating circulating nucleic acids. The preserved urine sample may be processed for isolating any circulating tumor cells, minimal residual disease and pathogens for diagnostic analysis. 
         [0011]    The method may include a preservative delivery vessel for dispensing into a specimen container a predetermined amount of a urine preservative. The preservative delivery vessel may include a dispensing nozzle portion that includes a sealed tip that is capable of being ruptured to define a nozzle opening. The preservative delivery vessel may include an elongated hollow barrel portion in fluid communication with the dispensing nozzle portion. The barrel portion may contain a bodily fluid preservative composition. The barrel portion may have an initial internal volume and a flexible wall structure that is capable of being squeezed manually by a user (e.g. in the absence of any assistive tool) for reducing the initial internal volume to a smaller volume and applying pressure to advance the preservative composition towards and through the nozzle opening after the sealed tip is ruptured. 
         [0012]    The teachings herein further contemplate that the methods disclosed herein result in preserving circulating cell-free DNA in urine over a wide range of dilution ratios within temperature fluctuations that can occur during urine sample handling, storage and transportation. The urine sample preservation method and preservative delivery vessel provide a method for obtaining high quality stabilized urinary cell-free DNA for clinical diagnostics development and application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  compares the results of unpreserved urine samples and urine samples treated with a composition typically used for blood stabilization including 0.17% K 3 EDTA. 
           [0014]      FIG. 2  compares the results of unpreserved urine samples and unpreserved urine samples treated with 0.9% K 3 EDTA alone. 
           [0015]      FIG. 3  compares the results of unpreserved urine samples and urine samples treated with the urine preservative composition of the present teachings containing at least 0.9% K 3 EDTA in addition to a formaldehyde scavenger and a stabilizing agent. 
           [0016]      FIG. 4  illustrates a perspective view of the preservative delivery vessel taught herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the teachings, its principles, and its practical application. Those skilled in the art may adapt and apply the teachings in its numerous forms, as may be best suited to the requirements of a particular use. Accordingly, the specific embodiments of the present teachings as set forth are not intended as being exhaustive or limiting of the teachings. The scope of the teachings should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. Other combinations are also possible as will be gleaned from the following claims, which are also hereby incorporated by reference into this written description. 
         [0018]    This application claims the benefit of the filing date of U.S. Provisional Application No. 62/128,774, filed Mar. 5, 2015. The entirety of the contents of that application are hereby incorporated by reference for all purposes. 
         [0019]    The urine preservative composition provides for stabilization of cell-free nucleic acid in a urine sample. The urine sample includes nucleic acids which may be include one or more of cell free nucleic acids, circulating tumor nucleic acids, cellular nucleic acids, DNA, RNA, microRNA (miRNA), or messenger RNA (mRNA). The urine preservative composition may include one or more stabilizing/preserving agents. The one or more stabilizing/preserving agents may be formaldehyde releasing agents. The urine preservative composition may include one or more formaldehyde quenching agents. The urine preservative composition may include one or more nuclease inhibitors. The urine preservative composition may comprise a stabilizing/preserving agent, a formaldehyde quenching agent and a nuclease inhibitor in an amount that is greater than the amount required for stabilizing cell-free nucleic acid in blood. Considering the relatively minor in nuclease activity in urine, it is surprising that such a significant increase in nuclease inhibitor (as compared to blood stabilizers) is required to compensate for the increase in nuclease activity. 
         [0020]    The method may include contacting the urine sample while within the sample specimen container with a urine preservative composition that includes a formaldehyde releasing agent and a quenching agent. The quenching agent may be present in an amount sufficient to react with any free formaldehyde so that the free formaldehyde (e.g., all of the free formaldehyde) reacts to form a reaction product that is inert. The urine preservative composition may also include a nuclease inhibitor in an amount significantly greater than that utilized for blood stabilization, much more than would be expected considering the minor increase in nuclease activity in urine as compared to blood. 
         [0021]    Effective stabilization of the nucleated blood cells present in urine serves to prevent contamination of the native cell free DNA compliment present in fresh urine. Nucleated blood cell stabilization reduces the level of contaminating genomic DNA in the overall DNA yield. One of the most significant challenges with respect to the detection of actionable mutations in cell free DNA and or ctDNA is the instability of the nucleated blood cells in the urine (i.e. white blood cells) after collection (which instability may be increase as compared to a blood sample). Without steps to stabilize the sample, nucleated blood cells break down post blood draw, resulting in an increase in genomic DNA (gDNA). The increased gDNA serves to dilute the mutation derived DNA (the cell-free nucleic acid being sought) making it much more difficult to detect the actionable mutations and requiring that the techniques be more sensitive than those used for mutation detection performed w/ tissue analysis. 
         [0022]    The stabilizing/preserving agent may effectively stabilize/preserve the nucleated blood cells in the urine sample. The stabilizing/preserving agent may prevent cell lysis/breakage that can occur during urine sample handling/storage and or processing. Stabilizing/preserving agents that may be used include, but are not limited to diazolidinyl urea (DU), dimethylol urea, 2-bromo-2-nitropropane-1,3-diol, 5-hydroxymethoxymethyl-1-aza-3,7-dioxabicyclo (3.3.0)octane and 5-hydroxymethyl-1-aza-3,7-dioxabicyclo (3.3.0)octane and 5-hydroxypoly [methyleneoxy]methyl-1-aza-3,7-dioxabicyclo (3.3.0)octane, bicyclic oxazolidines (e.g. Nuosept 95), DMDM hydantoin, imidazolidinyl urea (IDU), sodium hydroxymethylglycinate, hexamethylenetetramine chloroallyl chloride (Quaternium-15), biocides (such as Bioban, Preventol and Grotan), a water-soluble zinc salt or any combination thereof. 
         [0023]    Effective stabilization also requires quenching substantially all available free formaldehyde that may be present from stabilizing/preserving agents which release formaldehyde. Free formaldehyde compromises or damages the integrity of the native DNA. If not quenched it will compromise or destroy the structural integrity of the actionable mutations in the cell free DNA and or ctDNA. Furthermore, the quenching of formaldehyde is even more important with regard to urine. As compared to a blood sample, a urine sample contains very few biological components with which the formaldehyde can react with. As a result any remaining free formaldehyde present in the sample will be able to cause damage to target nucleic acids. As a result, whereas blood samples only require minimal quenching of the free formaldehyde, urine samples require that all free formaldehyde be sufficiently quenched. 
         [0024]    The formaldehyde quenching agent quenches free formaldehyde that will in fact compromise or damage the integrity of the native DNA. Formaldehyde quenching agents that may be used include, but are not limited to glycine, Tris(hydroxymethyl)aminomethane (TRIS), urea, allantoin, sulfites or any combination thereof. 
         [0025]    Stabilization of cell-free DNA in urine further requires blocking of enzymatic active (i.e. DNase activity) in fresh urine to prevent the enzymatic activity that will rapidly hydrolyze nucleic acids. If not effectively blocked, the nucleic acid concentration will decrease quickly as a result of the enzymatic activity that will function to destroy the physical and structural integrity of the nucleic acids. Such enzymatic activity is higher than that found in typical blood samples, but an unexpectedly large increase (at least five times that used in blood stabilization) of nuclease inhibitor is required to compensate. 
         [0026]    The nuclease inhibitor inhibits nuclease activity in urine. Nuclease inhibitors that may be used include, but are not limited to ethylene glycol tetraacetic acid (EGTA), pepstatin, K 3 EDTA, phosphoramidon, leupeptin, aprotinin, bestatin, proteinase inhibitor E 64 (E-64), 4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) or any combination thereof. 
         [0027]    The urine sample preservative composition may comprise imidazolidinyl urea (IDU), diazolidinyl urea (DU,) or a combination thereof, a nuclease inhibitor and a formaldehyde scavenging agent. The urine preservative may also comprise imidazolidinyl urea (IDU), diazolidinyl urea (DU) or a combination thereof, glycine, and K 3 EDTA. The imidazolidinyl urea (IDU) may be present in a concentration (of the preservative composition post contact with a urine sample) of about 0.5% to about 2.0%. The imidazolidinyl urea (IDU) may be present in a concentration of about 0.20% to about 4.0%. The glycine may be present in a concentration of about 0.01% to about 0.2%. The glycine may be present in a concentration of about 0.01% to about 0.4%. The glycine may be present in a concentration of at least about 0.01%, at least about 0.05%, at least about 0.2%, or even at least about 0.3%. The K 3 EDTA may be present in a concentration of about 0.5% to about 2.0%. The K 3 EDTA may be present in a concentration of about 0.50% to about 3.6%. The K 3 EDTA may be present in a concentration of at least about 0.5%, at least about 1%, or even at least about 2.5%. The ratio of K 3 EDTA to imidazolidinyl urea (IDU) may be 5:2. The ratio of K 3 EDTA to imidazolidinyl urea (IDU) may be from about 1:3 to about 3:1 (e.g., about 9:10, about 9:5 or even about 9:20). The ratio of K 3 EDTA to glycine may be from about 5:1 to about 100:1 (e.g., about 50:1 or even about 9:1). The urine preservative may be present in an amount of about 1 to about 20 percent by volume of the specimen container. The urine preservative may be present in an amount of about 1 to about 20 percent by volume of the specimen container. As compared with a composition for stabilizing blood, the composition presented herein for stabilizing urine may have an increased amount of nuclease inhibitor and/or an increased about of formaldehyde quenching agent. 
         [0028]    The urine sample may be diluted 5:1 with the preservative agent. For example, 4 parts urine specimen to 1 part urine preservative reagent. The urine sample may be diluted 20:1 with the preservative agent. For example, 19 parts urine specimen to 1 part urine preservative reagent. The urine sample may be diluted 30:1 with the preservative agent. For example, 29 parts urine specimen to 1 part urine preservative reagent. 
         [0029]    The sealed vessel of urine preservative may be a single unit dose. The single unit dose may hold a premeasured amount of preservative. The single unit dose may be used for a preserving a single specimen sample. The single unit dose may be labeled with the amount of preservative in the unit dose. The sealed vessel may be a non-reusable container designed to hold a specific amount of preservative. [ 0030 ]The urine preservative may be directly contacted with urine sample or the urine sample may be directly contacted with the urine preservative. The contacting step may take place at the collection site. Preferably the contacting step occurs within two hours of obtaining the specimen. 
         [0030]    The shipping temperature of the sealed specimen container may be within a range from about 6° C. to about 37° C. The sealed specimen container may be transported without refrigeration or freezing of the preserved urine sample. 
         [0031]    The preserved urine sample may exhibit a stability for at least about 7 days post treatment. The preserved urine sample may preserve the original proportion and integrity of nucleic acids in the preserved urine sample. The preserved urine sample may minimize release of cellular nucleic acids from nucleated cells and stabilize nucleic acids. The preserved urine sample may stabilize cell-free nucleic acids in urine at 6° C., 22° C. and 37° C. for at least 7 days. 
         [0032]    The step of analysis may be performed 1, 2, 4, or 7 days after the specimen is obtained. The analysis of the urine sample may include urinalysis testing. The analysis of the urine sample may include amplification and quantification of nucleic acids using PCR. The analysis of the urine sample may include nucleic acid sequencing techniques. The analysis of the urine sample may include isolating nucleic acids from the preserved urine sample and analyzing the isolated nucleic acids to identify a pathological condition. 
         [0033]    The urine sample method may be performed in the absence of refrigeration of the preserved sample. The urine sample method may be performed in the absence freezing the preserved sample. The preserved sample may be stored at room temperature for a period of least 7 days. 
         [0034]    The preservative composition may be present in an amount of about 1 ml to about 15 ml in the preservative delivery vessel. The preservative composition may be present in an amount of about 5 ml to 10 ml in the preservative delivery vessel. The preservative composition may be present in an amount of about 3 ml to about 5 ml in the preservative delivery vessel. 
         [0035]    The preservative delivery vessel may be packaged in a plurality of vial strips of single unit dosages. The plurality of vial strips may be packaged in carton. The plurality of vial strips may be packaged as part of a diagnostic kit. The plurality of vials strips may be detachable. The plurality of vial strips may be separated from each other by tearing along a perforation. The plurality of vial strips may be separated from each other by cutting along a specified marking. 
         [0036]    The preservative delivery vessel may be formed by injection molding. The preservative delivery vessel may be an injection molded unit dose vial. The injection molding material may include thermoplastic or thermosetting polymers. 
         [0037]    The effect of different urine preservative concentrations on stability of urinary cf DNA was examined and compared to untreated urine samples. Untreated urine samples showed a significant decrease in cell-free DNA concentrations of both oncogene KRAS and housekeeping gene β-actin on day 4 and 7 post specimen collection at room temperature. In contrast, cell-free DNA concentrations remained stable for at least 7 days in urine samples treated 5:1 to 30:1 with urine preservative. Moreover, the preservative reagent also stabilized cell-free DNA in urine at 6° C., 22° C. and 37° C. for up to 7 days, whereas untreated samples showed a significant degradation of cell-free DNA at 22 ° C. and 37° C. 
       EXAMPLES 
       [0038]    To study the effect of different urine preservative concentrations on the stability of urinary cell-free DNA, treated urine samples are examined and compared to untreated urine samples. The first-voided morning urine samples are diluted 5:1, 20:1 or 30:1 with the preservative reagent and stored at room temperature with untreated urine specimens in parallel. Aliquots are removed at specified time points. Cell-free DNA is purified from urine and quantified by a Droplet Digital PCR (ddPCR) assay. 
         [0039]    The first-voided morning urine collected from healthy volunteers is treated with urine preservative and is stored at specified temperatures with untreated samples in parallel. Aliquots of urine (5 mL) are removed from each sample on day 0, 4 and 7, respectively. These aliquots are centrifuged at room temperature at 4000 rpm for 10 minutes. 4 mL of supernatant is carefully removed without disturbing pellets and transferred to a new tube using a pipette followed by cfDNA extraction. Urine cfDNA is purified using the commercially available QIAamp® Circulating Nucleic Acid Kit (QIAGEN®, Santa Clarita, Calif.). For optimal results, the manufacturer&#39;s recommended protocol is modified slightly by increasing the duration of the proteinase K treatment from 30 min to 1 hour at 60° C. The PCR is performed using the QX100 Droplet Digital PCR system (Bio-Rad, Hercules, Calif.). The KRAS copy number assay kit is purchased from Applied Biosystems (Foster City, Calif.). Primers and the probe for the ddPCR quantification of human β-actinare purchased from Integrated DNA Technologies (Coralville, Iowa). 
         [0040]    Results show urinary cfDNA is stabilized by urine preservative over a wide range of dilution ratio at room temperature. Urine was treated 5:1, 20:1 or 30:1 with the urine preservative disclosed herein and stored at room temperature. On day 0, 4 and 7, cfDNA is isolated from urine samples and quantified by ddPCR. The concentration of KRAS gene decreased significantly in untreated urine on day 4 and 7, whereas it remained stable in all treated urine samples for at least 7 days post specimen collection 
         [0041]    To study the effect of storage temperature on cell-free DNA concentration, both treated and untreated urine samples were stored at 6° C., 22° C. and 37° C. Similarly, cell-free DNA was extracted at various time points and quantified by ddPCR. 
         [0042]    The first-voided morning urine collected from healthy volunteers was treated with urine preservative and stored at specified temperatures with untreated samples in parallel. Aliquots of urine (5 mL) are removed from each sample on day 0, 4 and 7, respectively. These aliquots are centrifuged at room temperature at 4000 rpm for 10 minutes. 4 mL of supernatant was carefully removed without disturbing pellets and transferred to a new tube using a pipette followed by cfDNA extraction. Urine cfDNA is purified using the commercially available QIAamp® Circulating Nucleic Acid Kit (QIAGEN®, Santa Clarita, Calif.). For optimal results, the manufacturer&#39;s recommended protocol is modified slightly by increasing the duration of the proteinase K treatment from 30 min to 1 hour at 60° C. The PCR was performed using the QX100 Droplet Digital PCR system (Bio-Rad, Hercules, Calif.). The KRAS copy number assay kitiss purchased from Applied Biosystems (Foster City, Calif.). Primers and the probe for the ddPCR quantification of human β-actin are purchased from Integrated DNA Technologies (Coralville, Iowa). 
         [0043]    Results show urinary cfDNA stabilized by urine preservative at various storage temperatures. Urine samples are treated 20:1 with urine preservative and stored at 6° C. or 37° C., respectively. cfDNA is isolated from urine samples at specified time points and quantified by ddPCR. The cfDNA (KRAS) is stabilized in all treated urine samples for at least 7 days at either 6° C. or 37° C. No statistically significant difference in cfDNA concentration is found between stored samples and day 0 samples. Similar results are observed for the house keeping gene β-actin. 
         [0044]    Examples 1 and 2 demonstrate the effect of different urine preservative concentrations on stability of urinary cfDNA compared to untreated urine samples. Untreated urine samples show a significant decrease in cfDNA concentrations of both oncogene KRAS and housekeeping gene β-actin on day 4 and 7 post specimen collection at room temperature. In contrast, cfDNA concentrations remained stable for at least 7 days in urine samples treated 5:1 to 30:1 with urine preservative. Moreover, the preservative reagent also stabilized cfDNA in urine at 6° C. or 37° C. for up to 7 days. 
         [0045]    In addition, the effect of different reagent formulations on stability of urinary cfDNA is examined and compared to untreated urine samples. The urine samples are diluted with various reagent formulations and stored at room temperature with untreated urine specimens in parallel. Aliquots are removed at specified time points. cfDNA (β-actin) is purified from urine and quantified by a Droplet Digital PCR (ddPCR) assay. 
         [0046]      FIG. 1  compares the results of unpreserved urine samples and urine samples treated with a reagent for stabilizing blood including about 300 to about 700 g/L IDU, from about 60 to about 100 g/L K 3 EDTA, and about 20 to about 60 g/L glycine. Results show the reagent for stabilizing blood does not effectively block urine nuclease activity, resulting in DNA degradation. A decrease in cfDNA is associated with nuclease activity and an increase with genomic DNA (unstable WBC). Results indicate that the reagent for stabilizing blood fails to stabilize cfDNA in urine. 
         [0047]      FIG. 2  compares the results of unpreserved urine samples and unpreserved urine samples treated with 0.9% K 3 EDTA. The treated urine samples were treated with a K 3 EDTA concentration at around 5× the concentration contained in a commercial K 3 EDTA blood collection tube (i.e. 0.17% vs. 0.9%). The nuclease activity was completely blocked by increasing the concentration of the nuclease inhibitor. Results indicate treatment with 0.9% K 3 EDTA prevents degradation of the native cell free DNA compliment in urine. However, cellular DNA is released in the absence of an effective nucleated blood cell stabilizer (i.e. WBC degradation). 
         [0048]    Urine conditions are markedly different from those of blood. Fresh urine has a higher DNase activity as compared to blood plasma. As seen in  FIG. 1 , in the absence of nuclease inhibition the native cell free DNA present in fresh urine is grossly unstable, regardless of the presence/concentration of the fixative/stabilizer as commonly used in blood stabilization.  FIGS. 1 and 2  illustrate the marked need for a heightened level of nuclease activity inhibition. 
         [0049]      FIG. 3  compares the results of unpreserved urine samples and urine samples treated with the urine preservative composition disclosed herein. The treated urine samples were treated with a urine preservative composition including about 300 to about 700 g/L imidazolidinyl urea (IDU), about 0.9% K 3 EDTA (e.g., from about 100g/L to about 300 g/L) and at least about 30g/L glycine. The results indicate that the urine preservative composition stabilizes cfDNA in urine. Therefore, the present teachings provide a preservative reagent that can preserve the original proportion and integrity of cfDNA in urine post specimen collection. 
         [0050]      FIG. 4  shows an example container for carrying the urine preservative composition in accordance with the teachings herein. Each individual container can be separately opened and added to a urine sample in accordance with the teachings herein. 
         [0051]    The explanations and illustrations presented herein are intended to acquaint others skilled in the art with the invention, its principles, and its practical application. Those skilled in the art may adapt and apply the invention in its numerous forms, as may be best suited to the requirements of a particular use. Accordingly, the specific embodiments of the present invention as set forth are not intended as being exhaustive or limiting of the invention. The scope of the invention should, therefore, be determined not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. Other combinations are also possible as will be gleaned from the following claims, which are also hereby incorporated by reference into this written description.