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Are urine strips accurate?

A positive urine dipstick has a great chance of being false positive. The average of the positive predictive value in the studies shows 61 percent. However, a negative urine dipstick seems to be more reliable, in which the negative predictive value shows an average of 83 percent.

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Sensitivity and specificity

Sensitivity indicates the urine dipstick’s ability to discover whether the patient has bacteriuria. Sensitivity varied considerably in the included studies. Juthani-Mehta et al. (23) reported that a urine dipstick that showed presence of nitrite or leukocytes or both, had a sensitivity of 100 per cent. On the other hand, Arinzon et al. (22) reported a sensitivity of 72 per cent. All studies do not report on the sensitivity to nitrite and leukocytes alone, but in the studies that do, the results vary from 69 – 98 per cent on leukocytes and from 54 – 83 per cent on nitrite. As opposed to sensitivity, specificity is used to describe the urine dipstick’s ability to uncover whether the patient does not have bacteriuria. The specificity varies in the various studies. Juthani-Metha et al. (23) looked at cases where the urine dipstick is positive for leukocytes and nitrite, or for either one. The specificity is then 20 per cent. Ducharme et al.’s Canadian study (26), however, reports a specificity of 70 per cent. When only leukocytes are examined, the specificity is 26 – 81 per cent. Nitrite, on the other hand, has a specificity of 48 – 100 per cent.

Positive predictive value and negative predictive value

Positive predictive value (PPV) and negative predictive value (NPV) tell us about the probability of the urine dipstick giving a correct result. All the studies, except Evans et al. (25), say something about PPV and NPV when both leukocytes and nitrite are present, or when leukocytes or nitrite alone is indicated on the urine dipstick. PPV shows a percentage from 31 – 93 in the various studies, whereas NPV varies from 49 to 100 per cent.

Other relevant findings

All six studies included, except Evans et al. (25), looked at both leukocytes and nitrite as reagents. This indicates that either nitrite or leukocytes were present, or that the urine dipstick reacted to both variables. Several studies also looked at whether there were indications of proteins and blood. With respect to protein and blood, none of the studies showed that these reagents have any significance in establishing bacteriuria if this is indicated on the urine dipstick. Indications of protein and blood are thus not reliable indicators of UTI. Further, Sundvall et al. also compare manual reading of urine dipsticks with an automatic analyzer of the type Clinitek 50. The study shows that the test method does not make a difference, the results are equally good or bad with manual as with automatic reading.

Little research on the subject

UTI is one of the most common bacterial infections in the older population. Nevertheless, UTI is often overdiagnosed and overtreated among the elderly based on unspecific clinical indications and symptoms and a high prevalence among the elderly of ASB (5) that should not be treated, according to clinical guidelines (7, 9, 28). Although a urine dipstick is unable to distinguish between an ASB and a UTI, urine dipsticks are commonly used to diagnose UTI in elderly patients. Urine dipsticks are frequently used in the clinic, and antibiotic treatment may be initiated based on a positive urine dipstick test until a urine culture result is available (26). As urine dipsticks appear to be much used in the clinic and the results of urine dipstick tests have a crucial role in diagnosing UTI in the elderly, it is interesting to see how reliable urine dipsticks are. The purpose of this literature study was to assess the reliability of urine dipsticks in diagnosing UTI in elderly patients in nursing homes and home care services. In spite of extensive and systematic literature search, we found only six research articles dealing with this subject. This low number makes one wonder, considering the widespread use of urine dipsticks. Much research is done on urine dipsticks in other populations such as children, working adults and predominantly on women. These studies give various results depending on age group and patient criteria (21). Much research is done on pregnant women as a group, and in this population urine dipsticks are recommended used to discover bacteriuria (18). There is, however, not much research on the combination of elderly and the use of urine dipsticks; this is supported by Bevridge et al. (5). This literature study is therefore an important contribution to knowledge on the use of urine dipsticks in a population much plagued with UTI, but with a high prevalence of ASB.

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Using urine dipsticks in the clinic

When the general condition or behaviour of an elderly patient changes today, UTI is generally the first suspect. A urine dipstick is a simple, inexpensive and non-invasive tool for confirming or excluding whether a patient has UTI, and is therefore frequently used. If a urine dipstick proves positive for nitrite and leukocytes, common practice is to contact a physician (17), oftentimes by telephone, and antibiotics are prescribed (29). The widespread use of urine dipstick tests in Norway is not surprising. Norwegian guidelines for prescription of antibiotics in the primary health services (7) state that testing for leukocytes and nitrite on a urine test strip may help establish whether an infection is present. The guidelines also state that microscopy of the urine will not yield any additional information to the use of urine dipsticks, that leukocytes have good test value (sensitivity and specificity are around 85 per cent), and that a positive nitrite test corresponds with gram-negative strings when the urine has remained four hours in the urine bladder (specificity 96 per cent) (7). In other words, Norwegian guidelines have great faith in urine dipsticks as a diagnostic tool.

Nurses have a central role

One study shows that doctors often choose to prescribe antibiotics on the basis of a positive urine dipstick test until a culture is available (30). This approach has, however, turned out to have a margin of error of 20 to 40 per cent. Such erroneous diagnoses are very unfortunate as treating older adults with antibiotics may lead to the development of resistance and unwanted side effects. In worst case it may keep one from discovering other, underlying, causes of the patients’ symptoms (2, 10). The nurse has proved to have a central role in diagnosing UTI in the elderly. The nurse observes the patients’ condition and symptoms on a daily basis, prescribes the urine culture, uses the urine dipstick and influences the initiation of antibiotics (17). That is why it is important that nurses have knowledge on UTI in the elderly, so that they may make the correct assessments. Part of this assessment is to be able to interpret and know the limitations of the urine dipstick.

Is the urine dipstick a reliable tool?

The more recent studies included in this literature review (21 – 23, 26) emphasise that the urine dipstick is not a good enough tool in confirming bacteriuria in elderly patients. The studies point to results with many false positives and with low sensitivity and specificity, i.e. urine dipsticks are not reliable in distinguishing between health and illness with regard to UTI. Duchrame et al. (26) found that 61 per cent of patients with a positive urine dipstick test did not have bacteriuria according to the urine culture. Sundvall et al. (21) showed that with a positive urine dipstick test the probability of bacteriuria is just 51 – 73 per cent. Deville et al. (31) have done a meta-analysis where they conclude that urine dipsticks alone may be useful in all populations to exclude the presence of infection when there are no positive findings of nitrite or leukocytes. Even if this meta-analysis is based on a small number of articles on the elderly, the findings correspond well with the findings in the articles included in our literature review. The studies included have a NPV from 88-100 per cent with the exception of the Arinzon et al. study (22), which has a NPV of 49 per cent. This indicates that the urine dipstick is not a very reliable tool for establishing UTI, but that it is more reliable for excluding UTI in elderly patients.

No better tools

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Even if the urine dipstick is not very reliable in diagnosing UTI in the elderly, we have not so far found a better tool. A series of studies have been done to assess the reliability of other tools in diagnosing UTI. The McGeer criteria and the Loeb criteria are both short check lists for diagnosing UTI with the help of clinical signs such as rising temperature, burning pain at urination, frequent urination, suprapubic pain, change of character of urine, throbbing tenderness over kidneys, visible blood in the urine, urine incontinence and deterioration of mental condition (8, 32). Juthani-Mehta et al. did a study in 2007 where they assessed whether nursing home patients with suspected UTI met the Loeb or McGeer criteria, and whether they were in line with the laboratory results (33). Here the McGeer criteria turned out to have a sensitivity of 30 per cent, specificity of 82 per cent, PPV of 57 per cent and NPV of 61 per cent. The Loeb criteria showed almost the same results – that is, not very high reliability in diagnosing UTI. Juthani-Mehta et al. (34) did a study where they identified clinical signs in connection with bacteriuria and pyuria (white blood cells in the urine) in nursing home patients with suspected UTI. They showed that dysuria (painful urination), change in character of urine and change in mental condition were related to bacteriuria combined with pyuria, but this study gave no better results than diagnosis with urine dipsticks. Sundvall et al. (35) studied whether higher concentration of Interleukin-6 in the urine could indicate whether the patient had UTI with non-specific symptoms. Interleukin-6 is a mediator for infection and plays an important role in the regulation of the immune system. The substance can be examined with a urine analysis. This study showed that neither increased concentration of Interleukin-6 in the urine or the use of urine dipsticks is suitable as indicator of unspecific symptoms and bacteria in the urine in the elderly population.

Implications for practice

As mentioned, the urine dipstick is a quick, non-invasive and inexpensive tool, but apparently not very reliable. As we do not seem to have any other, better, tool, it may be appropriate to continue using the urine dipstick, given that the method is used properly and interpreted correctly. The nurse must know the limitations of the urine dipstick. In Figure 3 (4, 7-10, 13-16, 36) we attempt to give an overview of the urine dipstick’s limitations with regard to the factors that may give false positives and false negative answers. Such knowledge will be of great value to the nurse in assessing the reliability of a urine dipstick result. Figure 3 may also be used as a clinical guide for when to use urine dipsticks and how to proceed after having collected the urine sample.

sykepleien.no - Can we trust urine dipsticks? - Sykepleien

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