Why is urine specimen integrity vital

Some other drugs can affect your results as well. Tell your doctor about any substances you use before doing a urinalysis. There, you can privately urinate into the cup. You may be asked to obtain a clean catch urine sample. This technique helps prevent bacteria from the penis or vagina from getting in the sample.

Begin by cleaning around your urethra with a premoistened cleaning wipe provided by the doctor. Urinate a small amount into the toilet, then collect the sample in the cup.

In some cases, your doctor may request that you do the urinalysis using a catheter inserted into your bladder through your urethra. This may cause mild discomfort.

The sample will then be sent to a lab or remain in the hospital if they have the necessary equipment. In the microscopic exam, your doctor looks at drops of your urine under a microscope. They look for:. For the dipstick test, your doctor inserts a chemically treated plastic stick into your sample. The stick changes color based on the presence of certain substances. This can help your doctor look for:. High pH levels can indicate urinary tract or kidney issues.

And any presence of sugar can indicate diabetes. If you have no other symptoms of an underlying condition and a physical exam shows that your overall health is normal, your doctor may not require a follow-up. Your urine normally contains a negligible level of protein. Sometimes, protein levels in your urine can spike due to:. But abnormally high levels of protein in your urine can be a sign of underlying issues that can cause kidney disease, such as:.

Your doctor may order follow-up tests to identify any conditions causing abnormally high protein levels in your urine. If your urinalysis results come back abnormal, your doctor may require additional tests to determine the cause. These can include:. There appears to be a variable loss of these figurated elements in manual methods due to the many intermediate steps involved centrifugation, decantation and resuspension of the specimen.

Moreover, automation allows a better standardization of particle analysis 4 , When counting equal ranges of particles, microscopy is generally inferior to automated methods 50 , Neutrophil gelatinase associated lipocalin NGAL is an emerging biomarker in the diagnosis of acute kidney injury. However, urinary tract infection and urinary neutrophil counts affect urinary values of this protein. In parallel, a correlation between NGAL and the bacterial count has been reported.

In leukocyturia or tubular damage e. As most drugs are characterized by a predominantly renal excretion, urine is the preferred specimen for inexpensive, noninvasive and quick substance abuse tests The Clinical and Laboratory Standards Institute CLSI developed guidelines concerning specific requirements for the technical performance of urinary drug testing The European Workplace Drug Testing Society 58 , the Substance Abuse and Mental Health Services 59 , the Swiss Working Group for Drugs of Abuse Testing Guidelines 60 , the Joint Technical Committee 61 and the United Kingdom 62 proposed some criteria for urine validity testing based on several parameters: urinary creatinine concentration, specific gravity, nitrite, pH and presence of exogenous or endogenous substances.

After checking of the integrity of the sample, positive screening tests are followed by confirmation methods It should be stressed that an appropriate collection, handling and testing of urine samples are necessary to avoid false-positive, false-negative and inconclusive test results Several specimen tampering methods have been used to avoid detection: substitution of urine by another fluid, adulteration by addition of a foreign material, dilution of the urine sample by adding water.

False-positive results can also be caused by operator errors, cleaning the skin with isopropyl alcohol, contamination of equipment, specimen confusion, mislabeling and misidentification of the subject, breaks in the chain of custody and errors during the measurement process To decrease the incidence of preanalytical problems, several precautions should be taken into account.

An identification and laboratory data system should be implemented; the condition of seals, shipping cartons, specimen containers and urine specimens should be checked for integrity; the information on the specimen requisition form and the external chain-of-custody form should be reviewed for completeness and accuracy Finally, over-the-counter OTC drugs, prescribed medications and some foodstuff, which are chemically related to drugs of abuse, can also be detected by urinary drug tests Amphetamine-related OTC drugs ephedrine, pseudoephedrine and phenylpropanolamine are known for their cross-reacting capacities with amphetamines screening immunoassays False-positive opiate drug tests have been reported after poppy food ingestion To reduce cross-reactivity and to increase drug specificity, many drug tests are routinely modified The monitoring of the impact of the preanalytical steps on urine sample quality and stability can be fulfilled by 1H NMR metabolic profiling.

Standard operating procedures SOPs for deposition in biobanks have been proposed Stability of the urine metabolic profile at various storage temperatures was studied for different preanalytical treatments prestorage centrifugation, filtration and addition of sodium azide. A high speed may cause destruction of cells and a release of cellular components, affecting the NMR profile. The most distant from nonprecentrifuged samples are the samples precentrifuged at a speed in the 1,—3, RCF range, while samples precentrifuged at 11, RCF are slightly closer to the aliquots that do not undergo any precentrifugation.

If a mild precentrifugation 1,—3, RCF is applied, cellular components are spun down. The subsequent 14, RCF centrifugation of the supernatant is useful for elimination of suspended particles. Precentrifuged or non-precentrifuged samples show differences in metabolic profile, which are attributable to chemical shift changes. Soluble components released by cells in fresh urine may alter the physiochemical properties of the solution.

Presence of cellular components affects NMR profiles even if non-fresh samples are analysed. This effect is less pronounced after storage in liquid nitrogen. The two most commonly used preservation methods have been compared: addition of sodium azide and the use of filtration 69 with or without a precentrifugation step.

Spectral variations were followed after urine processing or thawing. Sample alkalinisation is consistent with shift variations for the He1 N-methylhistidine; also, changes in the chemical shifts of the resonances of xantine are observed with time.

Filtration stabilizes NMR spectra over time. The origin of changes that affect the NMR spectra can be the result of a combination of chemical reactions, bacterial growth and enzymatic activities of urine. Addition of additives is to be avoided since the required concentrations will generate NMR signals covering the resonance of metabolites and may affect the original NMR profiles. For the maintenance of the metabolome, time between collection and processing and the temperature at which urine specimens are kept during this time delay should be reduced Besides, the International Standards Organization ISO document lists particular requirements for quality and competence Looking at the most recent CLSI recommendations, it is stated that high quality urine samples can only be delivered by appropriate urine collection tubes made of clear plastic and with conical bases for microscopic analysis of urine sediment and leak-proof containers.

In addition, high quality pipettes and standardized microscope slides with calibrated volumes for analysis of urine sediment are essential. A second important preanalytical point is whether preservatives are used or not, as unpreserved samples can give rise to bacterial proliferation.

Refrigeration for storage or transportation should always be followed by equilibration to room temperature and well mixing before analysis. Besides the influence of clarity and colour of the urine samples, a number of substances can interfere with dipstick tests, according to the type of test strip. In comparison with random urine testing, the examination of chemical analytes is more reliable when timed sampling is used, which is however prone to pre-analytical errors.

Random urine samples have a higher contamination risk in comparison with midstream clean catch samples. False-positive results can also be caused by bacterial overgrowth due to delays in the transport of samples. Treatment with antibiotics prior to urine sampling can lead to false-negative reports.

Urinalysis plays a key role as an aid in the differential diagnosis of many renal and urologic diseases. The preanalytical phase, including biological collection, identification, storage and specimen transport, preparation for analyses of the specimen e.

For that reason we have presented guidelines for a correct preanalytical management of urine samples in a flowchart Figure 1. Flowchart illustrating the guidelines for a correct preanalytical management of urine samples. As urine samples are often collected by patients themselves, the analysis of urine is one of the most susceptible examinations to preanalytical issues. In addition to the insurance of correct sampling, the clinical lab should optimize transport and sample preservation.

Next to the use of a primary urine container, it is recommended to split the original urine sample into various smaller aliquots for morphological, microbiological and chemical analyses, decreasing the risk of contamination.

Implementation of vacuum systems has enabled swift transport of urine specimens and limits the risk of contamination and errors. The disruptive force generated by the vacuum on brittle figurated elements e. As modern urinalysis flow cytometry, automated microscopy is characterized by a low CV, preanalytical aspects of urinalysis are of growing importance.

Special attention should be paid to casts, the most brittle structures in sediment analysis. There is a call for novel studies to optimize the analysis of urine sediment.

The investigation of dysmorphic erythrocytes, in particular acanthocytes, is also important in the diagnosis of glomerular disorders. The analysis of urine sediment cannot yet be abandoned in the 21st century. The time lag between voiding and examination of urine is a limiting factor for the over-all diagnostic accuracy. No preservatives are needed for many chemical analytes examined with test strips, if the sample is refrigerated and the analysis can be performed within 24 hours.

If a delay cannot be avoided and refrigeration is not possible, urine containers prefilled with preservative boric acid alone or in combination with formate or other stabilizers may be used. Since in everyday routine, most of the clinical laboratories are receiving urine samples with delays of several hours, we recommend to use refrigeration as a preservative instead of chemical preservatives for urinalysis according to the guidelines of the NCCLS If commercially available preservatives are used, their influence on chemical properties and appearance of particles should be kept in mind.

Ideally, preservatives are present in a lyophilized form. An important interference of preservatives with several chemical assays has been demonstrated. Most urine preservatives were originally only intended for preventing bacterial growth and not to perform chemical analysis or particle counting.

The combined use of test strip analysis and particle analysis manual or automated as a first step before bacteriological analysis has been proposed by guidelines in different algorithms to assure efficient use of resources 4.

As there is currently no preservative that is able to stabilize urine for chemical and particle analysis, novel research projects are needed. Until the development of such a preservative, clinical labs need to prepare two aliquots. Only a preservative stabilizing both bacteria and urinary particles can be considered as a valid alternative for sample refrigeration. As urine metabolomics has become a hot topic, the European Consensus Expert Group Report has published a number of recommendations for biobanking procedures Limited stabilisation.

No stabilisation. Potential conflict of interest. National Center for Biotechnology Information , U. Journal List Biochem Med Zagreb v. Biochem Med Zagreb. Published online Feb Author information Article notes Copyright and License information Disclaimer. Received Sep 30; Accepted Nov This article has been cited by other articles in PMC. Abstract Urine may be a waste product, but it contains an enormous amount of information.

Keywords: flow cytometry, preservatives, sample preparation, urinalysis. Patient preparation and sampling procedures The laboratory is responsible for correct information regarding optimal patient preparation and best sampling procedure. Which precautions should be implemented? Which sampling procedure to choose for urinalysis? Which sampling container is preferable? Transport and preservation Is it a matter of time? Table 1a. Open in a separate window.

NA - data not available. Table 1b. Use of preservatives: why, which and when? Table 2a. Influence of preservatives on particle analysis by flow cytometry. Interfering effect of different urine components on test strip analyses Due to the presence of alkaline medication or stale urine, highly buffered alkaline urine pH 9 may result in false-positive test strip results for proteinuria.

Manual methods Several methods have been developed for the detection of urinary elements. Automated methods Combining sediment microscopy and selective test strip examination of urine helps to assure adequate specificity and sensitivity of urinalysis 4 , 45 , Analysis of acute kidney injury proteins Neutrophil gelatinase associated lipocalin NGAL is an emerging biomarker in the diagnosis of acute kidney injury.

Importance of the preanalytical phase in urine toxicology As most drugs are characterized by a predominantly renal excretion, urine is the preferred specimen for inexpensive, noninvasive and quick substance abuse tests Preanalytical aspects of urine metabolomics The monitoring of the impact of the preanalytical steps on urine sample quality and stability can be fulfilled by 1H NMR metabolic profiling.

Is there an influence of centrifugation on analysis results? Which is the preferable preservation method? What are the recommendations? Summary Urinalysis plays a key role as an aid in the differential diagnosis of many renal and urologic diseases. Figure 1. Influence of preservatives on test strip reactions. Footnotes Potential conflict of interest None declared.

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Urine Specimen Collection Guidelines. A collector is a person who instructs and assists employees at a collection site, who receives and makes an initial inspection of the specimen provided by those employees, and who initiates and completes the Federal Drug Testing Custody and Control Form CCF.