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Urine pH: the Effects of Time and Temperature after Collection

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Janine D Cook
Janine D Cook
Janine D Cook
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Kathy A Strauss at University of Maryland, Baltimore
Kathy A Strauss
Yale H Caplan at University of Maryland, Baltimore
Yale H Caplan
Charles Lodico at U.S. Department of Health and Human Services
Charles Lodico
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The Mandatory Guidelines for Federal Workplace Drug Testing Programs provide criteria for specimen validity testing, including urine pH cut-offs, to report a urine specimen as adulterated or invalid. Since the urine pH criteria for invalid classifications, ≥ 3 and < 4.5 or ≥ 9 and < 11, became effective in November 2004, a number of specimens with results within the upper invalid limits, typically in the range of 9.1 to 9.3, have been reported with no evidence of adulteration. This study evaluated the hypothesis that these pH findings were the result of exposure to increased environmental temperatures during specimen standing and transport. Indeed, increased storage temperatures were associated with increased urine pH, with the magnitude of the change related to both storage time and temperature. The pH values of specimens stored at −20°C are relatively stable, whereas pH results > 9 are achieved at storage temperatures of room temperature or higher. It is noteworthy that no condition(s) produced a specimen with a pH > 9.5. Degradation of nitrogenous urine analytes is most likely responsible for the noted increases in pH. These findings are intended to supplement information used by the Medical Review Officers who are responsible for interpreting such marginally invalid pH results.
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... The adsorption of purine metabolites such as uric acid, hypoxanthine, and xanthine is influenced by the urinary pH [14], which ranges from 4 to 9 [15]. Given that the pKa values of purine metabolites fall within this pH range, their protonation states fluctuate, altering their affinities for the metal surface and thereby significantly affecting their SERS spectral signatures [16,17]. ...
... To explore the effect of pH, we analyzed the SERS spectra of urine from patients with breast cancer (n = 18) and control subjects (n = 10), and compared the SERS spectra of urine at their initial pH (Figure 1a, black spectrum) with the SERS spectra of urine after we adjusted all samples to pH 5, 7, and 9 ( Figure 1a, orange, green, and blue spectra). The initial pH values of the urine samples ranged from 5 to 7, consistent with the normal physiological pH range of 4-9 [15]. The SERS spectra of urine at their initial pH were dominated by intense SERS bands corresponding to hypoxanthine (725, 1090, 1456 cm −1 ), while bands associated with uric acid at 811, 889, 1131, and 1515 cm −1 had lower-intensity. ...
... To explore the effect of pH, we analyzed the SERS spectra of urine from patients with breast cancer (n = 18) and control subjects (n = 10), and compared the SERS spectra of urine at their initial pH (Figure 1a, black spectrum) with the SERS spectra of urine after we adjusted all samples to pH 5, 7, and 9 (Figure 1a, orange, green, and blue spectra). The initial pH values of the urine samples ranged from 5 to 7, consistent with the normal physiological pH range of 4-9 [15]. The SERS spectra of urine at their initial pH were dominated by intense SERS bands corresponding to hypoxanthine (725, 1090, 1456 cm⁻ 1 ), while bands associated with uric acid at 811, 889, 1131, and 1515 cm⁻ 1 had lower-intensity. ...
Advancing Breast Cancer Diagnosis: Optimization of Raman Spectroscopy for Urine-Based Early Detection
Article
Full-text available
  • Feb 2025
Background: Surface-enhanced Raman spectroscopy (SERS) analysis of urine is a promising liquid biopsy technique for cancer detection. However, its clinical translation is hindered by two major challenges that impact classification efficacy. First, the SERS signal of urine is confounded by fluctuations induced by physiological differences in urine composition such as pH and dilution. Second, the molecular origin of the SERS signal of urine is incompletely understood, limiting the interpretability of machine learning classifiers in terms of specific biochemical markers. Methods: In this pilot study, we analyzed urine samples from breast cancer patients (n = 18) and control subjects (n = 10) at three pH levels (5, 7, and 9). Additionally, we analyzed simulated urine mixtures consisting of uric acid, hypoxanthine, xanthine, and creatinine in physiological concentrations to explain the variation in the SERS spectra at different pH values. Results: Urine at pH 9 yielded the most detailed spectral features. The SERS spectral pattern under alkaline pH reflected greater contributions from hypoxanthine, uric acid, and creatinine, while xanthine contributions diminished due to competitive interactions at the SERS substrate surface. Normalizing SERS signals to the creatinine band at 1420 cm⁻¹ effectively mitigated the confounding effects of urine dilution. Conclusions: Optimizing the pH to 9 and normalizing to creatinine significantly enhances the interpretability and accuracy of SERS-based urine analysis for cancer detection. These findings offer important theoretical and practical advancements for the development of SERS-based liquid biopsy tools for cancer detection.
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... However, the 1 H NMR chemical shifts used for metabolite assignments are sensitive to local micro-environments, such as pH, ionic strength, and matrix compositions [13]. Thus, metabolite profiles extracted from individual urine samples can vary greatly across the wide pH range [14], leading to inaccurate data interpretation [15]. ...
Investigation of pH-dependent H NMR urine metabolite profiles for diagnosis of obesity-related disordering
Article
Full-text available
  • Dec 2024
  • INT J OBESITY
Background Human urine is highly favorable for ¹H NMR metabolomics analyses of obesity-related diseases, such as non-alcoholic fatty liver, type 2 diabetes, and hyperlipidemia (HL), due to its non-invasiveness and ease of large-scale collection. However, the wide range of intrinsic urine pH (5.5–8.5) results in inevitably chemical shift and signal intensity modulations in the ¹H NMR spectra. For patients where acidic urine pH is closely linked to obesity-related disease phenotypes, the pH-dependent modulations complicate the spectral analysis and deteriorate quantifications of urine metabolites. Methods We characterized human urine metabolites by NMR at intrinsic urine pH, across urine pH 4.5 to 9.5, to account for pH-dependent modulations. A pH-dependent chemical shift database for quantifiable urine metabolites was generated and integrated into a “pH intelligence” program developed for quantifications of pH-dependent modulations at various pH. The ¹H NMR spectra of urines collected from patients with Ob-HL and healthy controls were compared to uncover potential metabolic biomarkers of Ob-HL disease. Results Three urine metabolites were unveiled by pH-dependent NMR approach, i.e., TMAO, glycine, and pyruvic acid, with VIP score >1.0 and significant q-value < 0.05, that represent as potential biomarkers for discriminating Ob-HL from healthy controls. Further ROC-AUC analyses revealed that TMAO alone achieved the highest diagnostic accuracy (AUC 0.902), surpassed to that obtained by neutralizing pH approach (AUC 0.549) and enabled better recovering potential urine metabolites from the Ob-HL disease phenotypes. Conclusions We concluded that ¹H NMR-derived urine metabolite profile represents a snapshot that can reveal the physiological condition of humans in either a healthy or diseased state under intrinsic urine pH. We demonstrated a systematic analysis of pH-dependent modulations on the human urine metabolite signals and further developed software for quantification of urine metabolite profiles with high accuracy, enabling the uncovering of potential metabolite biomarkers in clinical diagnosis applications.
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... The generally accepted normal range for urine pH is 4.5-8.0; however, it is crucial to acknowledge that urine pH can vary based on several factors [15]. In instances of metabolic acidosis, urine pH tends to decrease and fall below 5, while a urine pH above 8 may indicate the presence of an infection caused by urea-splitting organisms such as Proteus mirabilis [16]. ...
The Asymptomatic Bacteriuria in the Patients with Epilepsy: A Cross-Sectional Study
Article
Full-text available
  • Nov 2024
Background Epilepsy is a chronic neurological disorder characterized by repetitive unprovoked seizures. While certain anti-seizure medications have been linked to urinary tract infections, limited information exists on the occurrence and risk factors of asymptomatic bacteriuria (ASB) in individuals with epilepsy. This study aims to investigate the prevalence and factors associated with ASB in patients with epilepsy. Method A cross-sectional study was conducted, enrolling patients with epilepsy and healthy adults as controls. All participants underwent urine analyses during follow-ups at an epilepsy special clinic. Data on epilepsy-related factors were thoroughly collected and analyzed. Descriptive statistics and a logistic regression model were employed to identify the prevalence and risk factors of ASB in patients with epilepsy. Results The study encompassed 200 patients with epilepsy, compared to 100 healthy controls. The prevalence of ASB in the epilepsy group was significantly higher than in the healthy controls (34.0 % versus 16.2 %, p = 0.001). The logistic regression model identified factors statistically associated with ASB in epilepsy, including gender (female) (p < 0.001), proteinuria (p = 0.021), and the use of oxcarbazepine (p = 0.011). Interestingly, lamotrigine demonstrated a protective effect against ASB (p = 0.023), along with age (p = 0.015) in this study. Moreover, patients with and without ASB exhibited a similar rate of 12 months of seizure freedom. Conclusion The prevalence of ASB is elevated in epilepsy, with identified risk factors including gender (female), proteinuria, and the use of the anti-seizure medication oxcarbazepine. Lamotrigine was found to be protective. These findings underscore the importance of clinician awareness, and careful monitoring of anti-seizure medication therapy.
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Ammonia Dynamics in the Human Body: Insights in Biomedical Sensing Technologies
Article
Full-text available
  • Apr 2025
Advancements in sensor technologies capable of measuring key biomarkers can greatly enhance medical diagnostics and health monitoring, facilitating more effective diagnosis, treatment, and prevention. While there are numerous biomarkers of interest, gaseous ammonia (NH3) stands out due to its significance as an indicator of organ function (e.g., liver and kidney failure) or bacterial infections (e.g., Helicobacter pylori, Proteus mirabilis) in the body. This review discusses the metabolism and presence of NH3 in body organs, as well as clinical conditions associated with the regulation of NH3 concentrations. This paper reviews various sensing materials and parameters, along with current state‐of‐the‐art gas sensors capable of detecting NH3 for biomedical applications. Additionally, it addresses the challenges faced by biomedical sensing technologies already in use in medical applications. This review highlights that while NH3 sensing applications for breath analysis are already well‐developed, in vivo NH3 sensing remains in its early stages and faces significant challenges. Finally, promising future research directions for NH3 sensing are discussed, including the integration of NH3 sensors in catheters or in the Simulator of Human Intestinal Microbial Ecosystem, as well as the early detection of antibiotic‐resistant bacteria to enhance medical diagnostics.
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A Miniaturized Device Based on Cobalt Oxide Nanoparticles for the Quantification of Uric Acid in Artificial and Human Sweat
Article
Full-text available
  • Mar 2025
Co3O4-based materials have multiple applications in the field of materials, especially in sensor technology. In this work, Co3O4 nanoparticles were synthesized using a chemical method. The crystalline phase and crystal size were investigated by XRD, the morphology by SEM and the oxidation states by XPS techniques. The Co3O4 material was used to immobilize the urate oxidase enzyme (UOx), which showed a higher current density (1.6 times higher) than the enzyme alone in cyclic voltammetry in phosphate buffer pH 5.6. GCE/Co3O4/UOx achieved a linear range of 3.7–500 µM and a higher sensitivity of 65 µA mM⁻¹ cm⁻² compared to 45 µA mM⁻¹ cm⁻² achieved by the enzyme alone in a uric acid sensor. The favorable activity of GCE/Co3O4/UOx enabled its use in a miniaturized device with low sample volume using artificial and real human sweat. The device was used to quantify uric acid levels in five samples and showed a relative error between the calculated and expected value of less than 10%. The implementation of GCE/Co3O4/UOx is attractive in a biosensor that can be used as a uric acid sensor in biological fluids.
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RENAL FUNCTION PARAMETERS OF HEALTHY CAPTIVE AND SEMICAPTIVE AMAZONIAN MANATEES (TRICHECHUS INUNGUIS)
Article
  • Dec 2024
Evaluating renal function is essential for managing captive wild animals, particularly threatened species like the Amazonian manatee (Trichechus inunguis) in rehabilitation and prerelease programs. A series of urine diagnostic tests, such as gross appearance, semiquantitative chemical analyses, microscopic review of sediments, and quantitative analyses of urea and creatinine, were performed in 57 free-catch urine samples. On the same occasion, 52 serum samples from the same individuals were analyzed for creatine kinase activity, creatinine, blood urea nitrogen, albumin, sodium, potassium, and chloride concentrations; serum symmetric dimethylarginine (SDMA) was measured for the first time in the species. Females had higher urine creatinine concentration (21.7 ± 11.8 mg/dl) and specific gravity (1.003 ± 0.003 mg/dl) than males (11.9 ± 8.5 mg/dl and 1.001 ± 0.002 mg/dl) (P < 0.01 for both). Males presented higher urine creatinine:urea ratio than females (24.8 ± 29.2 and 20.5 ± 29.2, respectively) (P < 0.05). Urine pH was lower in manatees from the semicaptive area (7.8 ± 0.6) than in manatees under human care (8.5 ± 0.6) (P = 0.02) using the benchtop pH meter but showed no difference between areas in the dipstick reaction (P = 0.71), given its lower sensitivity and narrower range detection. Furthermore, 18 and 75% of urine samples were positive for the presence of blood and/or nitrite, respectively, in the dipstick reaction, possibly because of sample contamination. Significant correlation was observed between serum blood urea nitrogen and urine urea concentrations (P = 0.02), and between serum and urine creatinine concentrations (P = 0.01). Serum SDMA did not differ between sex or between captive and semicaptive individuals. However, it positively correlated with urine (P = 0.02) and serum creatinine (P = 0.01) demonstrating its potential as a bioindicator of kidney function. The renal function of Amazonian manatees can be effectively assessed by urinalysis, especially when combined with serum biochemistry.
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Evidence of renal tubular injury in canine patients after elective desexing
Article
  • Oct 2024
Objective To investigate the frequency of perioperative acute kidney injury (AKI) in American Society of Anesthesiologists (SA) Grade I canine patients undergoing elective desexing using urine microscopy techniques and assess if pre‐ and intraoperative factors affect risk of developing AKI. Design Prospective observational clinical study conducted between September 2020 and October 2020. Setting University teaching hospital. Animals Thirty‐two female and four male dogs between 5 months and 5 years of age classified as ASA I undergoing elective desexing surgery. Methods Urinalysis was performed preoperatively and 20–24 h postoperatively to identify markers of renal tubular injury (RTI), particularly the presence of granular and renal tubular epithelial cell (RTEC) casts on sediment analysis. Dogs underwent a full physical examination and a preoperative assessment including measurement of urine specific gravity (USG), packed cell volume (PCV), total plasma protein and serum creatinine (sCr) was conducted as a part of the desexing programme. Anaesthetic records were examined for any evidence of intraoperative hypotension, defined as a mean arterial pressure (MAP) of <60 mmHg for any duration of time. MAP was measured using an indirect oscillometric technique. For analysis, animals were subdivided into affected and nonaffected groups, with affected animals those that had postoperative increases in granular and RTEC casts. Categorical and comparative analyses were then performed between groups to identify associations of increased casts with pre‐, intra‐ and postoperative variables. Results A frequency of RTI of 5.6% was identified. This was accompanied by a significant association between increases in casts with total duration ( p = 0.027) and number ( p = 0.016) of hypotensive episodes. Conclusions RTI is an anaesthetic consideration in ASA I veterinary patients undergoing elective desexing surgery. The identification of an association between the total duration and number of hypotensive episodes and the frequency of RTI highlights the importance of early detection of hypotension along with prompt and effective intervention in veterinary patients.
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Novel cobalt-based aerogels for uric acid detection in fluids at physiological pH
Article
  • Oct 2024
  • BIOSENS BIOELECTRON
A sensor for uric acid (UA) based on the urate oxidase enzyme (UOx) immobilized in novel Co-based aerogels with transition metals synthesized by the sol-gel method was developed and evaluated. The Co-based aerogels: Co, Ni-Co and Pd-Co were physicochemically characterized by XRD and HR-TEM. The surface area values of 53, 57 and 66 m2 g-1 were determined for Co, Ni-Co and Pd-Co, respectively by N2 adsorption-desorption technique. Co-based aerogels were mixed by cross-linking with UOx enzymes and electrochemically characterized in buffers at pH 7.4 and 5.6 (pH values reported for biological fluids such as blood and sweat) in the presence of different uric acid concentrations. Co-based aerogels with UOx showed improved performance as a uric acid biosensor compared to using the enzyme alone. At a pH of 7.4, a higher sensitivity of 11 μA μM􀀀 1 was obtained with Pd-Co/ UOx, 1.6 times higher than with UOx. At a pH value of 5.6, the highest sensitivity is achieved with Ni-Co/UOx. Stability and selectivity tests were performed in the presence of biological interferents without significant changes in the sensor. These results indicate a pleasing synergistic activity between Co-based aerogels and the enzyme.
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The Effects of Diet, Dietary Supplements, Drugs and Exercise on Physical, Diagnostic Values of Urine Characteristics
Article
Full-text available
  • Sep 2024
Background/Objectives: This review summarizes the current knowledge about factors that affect the physical characteristics of urine. It highlights proper urine sample collection and displays factors like diet, hydration status, and medications that can alter urine color, odor, clarity, specific gravity and pH. Results: Urinalysis is a minimally invasive examination of a patient’s health, especially concerning nephrological and endocrinological abnormalities, as well as dietary habits and stimulants used. Certain deviations in appearance, composition or frequency/pain during urination may indicate an ongoing disease process in the body. Based on laboratory results, further medical treatment is determined. The reason for a change in the color of the urine, for its clouding or intense odor may be a disease, as well as the consumption of food, medication, intensive physical exercise or inadequate hydration of the body. Well-standardized procedures for collecting, transporting, preparing and analyzing samples should become the basis for an effective diagnostic strategy in urinalysis. It is worth noting that pharmacists in pharmaceutical care are often the first people to whom a patient turns for health advice and for the interpretation of simple laboratory tests. Acquiring the ability to interpret the results of laboratory tests and the principles of proper sampling for laboratory tests is indispensable in the process of possible counseling and providing reliable answers to patients’ questions. Conclusions: Although urinalysis is not recommended as a routine screening tool for the general population, it can prove to be a valuable source of patient health data in some cases as the data will be useful to physicians and pharmacists to more effectively diagnose and better care for patients.
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Outpatient Urine Culture
Article
Full-text available
  • Sep 2000
  • ARCH INTERN MED
Background Dysuria is one of the most common presenting complaints of young women, and urinalysis is one of the most common laboratory tests performed. Despite the fact that the midstream clean-catch technique is commonly used for urine collection, contaminated urine cultures occur with distressing regularity. The midstream clean-catch technique is time-consuming to explain, frequently not performed correctly by patients, costly for supplies, often embarrassing for patients and staff, and of unproven benefit. Therefore, we designed a study to compare various methods of obtaining specimens for culture from acutely dysuric young women.Methods A total of 242 consecutive female patients who presented with symptoms suggestive of a urinary tract infection were randomized into 3 groups. The first group (n = 77) was instructed to urinate into a clean container. No cleansing was done, and the specimen was not obtained midstream. The second group (n = 84) was instructed to collect a midstream urine sample with perineal cleansing and spreading of the labia. In an attempt to decrease contamination from the vagina, the third group (n = 81) was given the same instructions as group 2, with the addition of using a vaginal tampon. Contamination rates were calculated for all 3 groups.Results Contamination rates for the 3 groups were nearly identical (29%, 32%, and 31%, respectively). Comparing the no-cleansing group with the combined cleansing, midstream groups also showed no difference in contamination rates (28.6% and 31.5%, respectively, with P = .65).Conclusions In young, outpatient women with symptoms suggestive of a urinary tract infection, the midstream clean-catch technique does not decrease contamination rates.
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Effectiveness of an outpatient urine screening program
Article
Full-text available
  • Jan 1978
We evaluated the effectiveness of a routine outpatient urinalysis screening program on a sample population of 2600 patients. The 189 abnormal urine results found in 182 patients were followed up by study of any new clinical and laboratory investigations or therapeutic modifications initiated on the basis of any abnormal test result. The urinalysis screening program appeared to have significant bearing on diagnosis or treatment in only 13 patients. Abnormalities found in 150 of the 182 patients were either not noted or no further positive action was taken. Thus we concluded that under the conditions of this study the urine screening program added to hospital costs without significant benefit to the patient.
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Investigation of the stability of drugs of abuse in urine sample by capillary zone electrophoresis
Article
  • Aug 1997
The stability of amphetamine and morphine in spiked or forensic urine samples after long-term storage was investigated using capillary zone electrophoresis (CZE). Both analytes were quantitatively determined in fresh or stored urine (for 3 to 10 months) in four kinds of containers (glass tube with rubber cap, glass tube with screw cap, PP plastic and PE plastic tube) at 4°C, -20°C, room temperature (RT) (25-27°C) or high temperature (HT) (35°C). Slight decrease of drug recovery was observed in samples stored at low temperatures (4 or -20°C) after 10 months, while those stored at higher temperatures (RT or HT) degraded dramatically. Both analytes totally disappeared in CZE electropherograms of forensic urine samples stored at HT for 10 months, The type of container used had little effect on the stability of the drugs. The results suggest: 1) all confirmed drug-positive urine samples should be stored frozen to maintain drug stability, and 2) CZE is a simple and convenient method for testing drug stability in urine.
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Determination of morphine and 6-acetylmorphine in plasma by high-performance liquid chromatography with fluorescence detection
Article
  • Jun 1991
  • J CHROMATOGR A
A method is described for the simultaneous determination of morphine and 6-acetylmorphine in small volumes of human plasma by normal-phase high-performance liquid chromatography using solid-phase extraction, dansyl derivatisation and fluorescence detection. The lower limits of quantitation in a 0.1-ml plasma sample are 10 ng/ml for morphine and 25 ng/ml for 6-acetylmorphine. The method has been applied to determine concentrations of morphine and 6-acetylmorphine in plasma samples from premature babies administered an intravenous infusion of diamorphine.
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Screening for drugs of abuse: Effect of heat-treating urine for safe handling of samples
Article
  • Jul 1990
Heating urine samples from high-risk patients for 1 h at 56 degrees C is no longer believed to completely inactivate human immunodeficiency virus (HIV; AIDS virus). To protect staff who are handling infectious samples such as those from drug-addiction units, heating at a higher temperature may be necessary. We report the stability to heat treatment (at 60, 70, and 100 degrees C) at pH 5.1 and 7.6 of some commonly abused drugs, namely, methadone, pethidine, amphetamine, the cocaine metabolite, benzoylecgonine, and the dextropropoxyphene metabolite nordextropropoxyphene. Heat-treating urine at 60 degrees C for 1.5 h or 70 degrees C for 1 h did not significantly affect the measured concentrations of these drugs. However, heat treatment at 100 degrees C for 1 h reduced the recovery of all the drugs. Benzoylecgonine and amphetamine were most susceptible to the different forms of heat treatment.
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