Review Preanalytical requirements of urinalysis Joris Delanghe*1, Marijn Speeckaert2 1Department of Clinical Chemistry, Ghent University Hospital, Gent, Belgium 2Department of Nephrology, Ghent University Hospital, Gent, Belgium *Corresponding author: [email protected] Abstract Urine may be a waste product, but it contains an enormous amount of information. Well-standardized procedures for collection, transport, sample preparation and analysis should become the basis of an effective diagnostic strategy for urinalysis. As reproducibility of urinalysis has been greatly improved due to recent technological progress, preanalytical requirements of urinalysis have gained importance and have become stricter. Since the patients themselves often sample urine specimens, urinalysis is very susceptible to preanalytical issues. Various sampling methods and inappro- priate specimen transport can cause important preanalytical errors. The use of preservatives may be helpful for particular analytes. Unfortunately, a universal preservative that allows a complete urinalysis does not (yet) exist. The preanalytical aspects are also of major importance for newer applications (e.g. metabolomics). The present review deals with the current preanalytical problems and requirements for the most common urinary analytes. Key words: flow cytometry; preservatives; sample preparation; urinalysis Received: September 30, 2013 Accepted: November 20, 2013 Introduction Urinalysis is the third major diagnostic screening 10-fold reduction in the analytical error rate over test in the clinical laboratory, only preceded by se- the last 30 years. Furthermore, also progress in in- rum/plasma chemistry profiles and complete formation technology and quality assurance meth- blood count analysis (1,2). For decades, microscop- ods have contributed to a further reduction of di- ic urine sediment analysis has been the gold stand- agnostic errors. Nevertheless, the lion share of er- ard (3). The introduction of new technologies and rors in laboratory diagnostics (and in urinalysis in automation has improved the accuracy and pro- particular) falls outside the analytical phase; both ductivity of the process (4). On the other hand, preanalytical and postanalytical steps are much consolidation of laboratories has increased the more vulnerable (7). physical distance between patient and laboratory, Various subphases have been identified in the pre- which creates a major preanalytical challenge. It is analytical phase of urinalysis. Need for the test, mandatory to focus on the preanalytical phase in collection and transport of the sample to the labo- order to improve the reliability of test results (5) ratory, receipt of the specimen by the laboratory and to lower the costs of health care (6). In the clin- and sample preparation and transport to the prop- ical laboratory, total quality could be defined as er laboratory section for testing (8) can be impor- the guarantee of a correctly performed activity tant potential sources of error. As more effort throughout the total testing process, providing needs to be spent in the preanalytical phase for valuable medical diagnosis and efficient patient the further reduction of errors (9), in the present care. Improvements in both reliability and stand- paper we give an overview of the preanalytical ardization of analytical techniques, reagents and challenges of urinalysis. instrumentation have contributed to a remarkable http://dx.doi.org/10.11613/BM.2014.011 Biochemia Medica 2014;24(1):89–104 ©Copyright by Croatian Society of Medical Biochemistry and Laboratory Medicine. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc-nd/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 89 Delanghe J, Speeckaert M. Preanalytical requirements of urinalysis Patient preparation and sampling wash products used for newborn and infant care procedures can potentially cause false positive screening test results, leading to involvement by social services The laboratory is responsible for correct informa- or false child abuse allegations (12). tion regarding optimal patient preparation and best sampling procedure. Interpretation of test re- Which precautions should be implemented? sults is only possible when these conditions are fulfilled. Informing the patient goes far beyond Minimizing contamination can already be achieved only explaining the practical aspects of urine sam- by implementation of simple precautive measures. pling. More specifically, the effect of possible bio- A 20% reduction of the number of false positive logical confounders such as dietary intake, diure- urine cultures can be achieved by washing the sis, exercise and other interferents, should be em- glans penis of men or the introitus of women phasized. If necessary, illustrated instructions for (10,13,14). Due to the influence on the viability of sampling can be provided (10). Despite the exist- bacteria, the use of soap or antiseptics is not rec- ing guidelines, the importance of a proper preana- ommended (10,15). lytical procedure for collecting urine specimens is usually not known by the patients. In a recent pa- Which sampling procedure to choose for per, Miler et al. showed that a 24-hour urine sam- urinalysis? ple was not properly collected in more than half of A large amount of sampling procedures is availa- the informed outpatients, which were often older ble with specific advantages and disadvantages. (mostly > 65 years) and suffering from a chronic When deciding the best procedure, one should disease. The prescribed instructions were not fol- take into consideration the patient’s characteris- lowed, some volume of the urine sample was dis- tics (suspected microorganisms or presence of a carded or an improper container was used. To de- urinary catheter). Sample quality can only be war- crease the number of errors in the preanalytical ranted if standardized instructions for urine collec- phase, laboratory staff, general practitioners and tion are available (10,13). Clean-catch urine or mid- patients should be educated and an active pro- stream portions of first morning urine samples col- moting of the preanalytical procedures by the lab- lected in a sterile urine container are the most oratory staff should be encouraged. In case of an commonly obtained specimens in routine prac- incorrect sample procedure, the urine collection tice. However, overnight bacterial growth in the should be repeated (11). bladder is likely, which can affect casts and cells. The quality of the reported results could also be Morphological studies showed a higher reproduc- influenced by variables in specimen processing. ibility when incubation time was ± 1-2 h. There- Sample preparation is more essential for different fore, using second morning urine specimens is particle analysis techniques in comparison with sometimes recommended (urine samples voided urine test strip analysis and microbiological cul- 2-4 h after the first morning urine) (16). In a recent ture. As an example of the importance of interfer- multicenter study (17), results obtained from first- ents, the influence of commercially available baby voided and mid-stream urine samples were com- soaps on tetrahydrocannabinol (THC) immu- pared. In healthy subjects, two consecutive sam- noassays can be mentioned. Beyond healthcare, ples of the first morning micturition were collected newborn drug screening plays also an important by a vacuum system, the first from the first-void role in the legal domain. Mixtures of drug-free and the second from the mid-stream. Routine uri- urine with various products that commonly con- nalysis was performed using dip-stick automated tact newborns were tested using immunoassays. analyzers and automated particle analyzers. Addition of variable commercially available baby Counts of epithelial cells, erythrocytes and leuko- soaps to drug-free urine resulted in a measurable cytes, but not for casts were significantly higher in response in THC immunoassays. Due to the pres- the first-voided samples. A significantly higher ence of surfactants with the THC assay, soap and count of epithelial cells, erythrocytes and leuko- Biochemia Medica 2014;24(1):89–104 http://dx.doi.org/10.11613/BM.2014.011 90 Delanghe J, Speeckaert M. Preanalytical requirements of urinalysis cytes was also observed between females and datory for bacteriological culture of urine samples. males in first-voided samples, whereas no signifi- Urine collection container design should enable cant difference could be found in mid-stream sam- easy sampling, ensuring an optimal transport and ples. Overall prevalence of subjects with cellular allowing sensitive detection of pathogens. Fur- elements count exceeding upper reference limits thermore, they should be free of interfering agents was also higher in first-voided than in mid-stream and made of non-absorbing materials, with no in- samples. Mid-stream urine was confirmed as the fluence on any analyte. The collection volume most appropriate sample, since the presence of should be determinant factor for the size of the contaminating elements, such as bacteria, analytes urine container. Additional requirements may be and formed particles are minimized (10). needed in function of diagnostic procedures (e.g. The European Confederation of Laboratory Medi- light sensitive analytes as porphyrins and uro- cine