Urine – to dip or not?

What?

An 84-year-old female was found on floor by carers. No obvious head injury and was alert on scene with some mild confusion. Paramedics had documented strong smell of urine and a collateral history from her family stated she had reduced oral intake recently and was not her normal self for the past few days.

On examination, all observations were within normal ranges although she appeared clinically dehydrated with a dry tongue and reduced skin turgor.

The nurse who was looking after patient came up and stated that they had done a urine dipstick test on the patient urine. The results showed:

  • leucocytes ++
  • blood +
  • nitrite positive.

So what?

Point of care urinalysis has been shown to be a useful test to determine the presence of bacteraemia in patients under the age of 65. Little et al. (2009) study found that urine dipstick results for nitrates  and either blood or leucocytes has a positive predicted value of 92% for bacteriuria. In relation to common findings (Simmerville et al 2005):

  • Leukocytes esterase is an enzyme produced by neutrophil.
  • The presence of nitrites is caused presence of bacteria, which change nitrates to nitrites.

Elderly patients (defined as those over 65 years) frequently have the presence of asymptomatic bacteriuria (ASB). The Scottish Intercollegiate Guidelines Network (SIGN 2012) guidelines for diagnosis of Urinary Tract Infection (UTI), define this as a urine culture that is positive for bacteria, in the absence of any urinary symptoms.

Nicolle et al (1983) took samples from male patients who were admitted to geriatric ward over 2 years, finding that 33% of patients had ASB. McMurdo and Gillespie (2000) also had similar findings with a range of 20-40% in their population.

The Scottish Antimicrobial Prescribing Group (SAPG 2013) decision aid for diagnosis and management of UTI in older people, suggests that urine dipstick tests should not be used to diagnose UTI in elderly. The decision aid suggests that a temperature above 37.9 or below 36 degrees with two or more clinical signs and symptoms should provide the diagnostic criteria. The clinical signs and symptoms suggested are shown below (The Scottish Antimicrobial Prescribing Group 2013,Loeb et al .2001):

  • Dysuria
  • Urgency
  • Frequency
  • New or worsening incontinence
  • Rigors
  • Flank pain
  • Suprapubic pain
  • Frank haematuria
  • New or worsening confusion

Additional data was reported by Orr et al. (1996) who enrolled patients in a residential home who developed a temperature and had urine cultures sent. They found that out of 179 positive urine cultures, only 23 patients had the required amount of clinical features to consider a UTI. They subsequently concluded that a urine culture cannot diagnose a UTI, but should instead be used as a tool to identify the correct antibiotic sensitivity.

There are no set criteria or golden rules for diagnosis of UTI however there are clinical features relating to pathophysiology that include dysuria, frequency and suprapubic pain. The SAPG (2013) guidelines are similar to the algorithm used by Loeb et al (2005) developed for guidance to reduce use of antibiotics for UTI. The use of the algorithm reduced the number of prescription for UTI by 31% in the nursing home who used the algorithm compared to those that did not.

 

Now What?

Elderly patients have ASB unless a UTI is suspected, so there is little point in performing a urine dipstick test. If UTI is suspected, consider all clinical features that can occur and not just that they are more confused than normal.

 

Jemma Owen

 

 

References

Little .P, Turner. S, Rumsby. K, Warner. G, Moore. M, Lowes. J.A, Smith .H, Hawke .C, Turner. D, Leydon. G.M, Arscott A & Mullee. M, (2009) Dipsticks and diagnostic algorithms in urinary tract infection: development and validation, randomised trial, economic analysis, observational cohort, and qualitative study. Health Technology Assessment. Volume: 13 Issue: 19.

Loeb,M., Bentley,D.W & Bradley,S. (2001) Development of a minimum criteria for the initiation of antibiotics in the residents of long-term care facilities: Results of a consensus conference. Infection Control Hospital Epidemiology. 22 120-124.

Loeb,M., Brazil,K., Lohfeld,L., McGeer, A., Simor,A., Stevenson,K.,  Zoutman,D., Smith,S., Liu,X & Walter, S.D. (2005) Effect of a multifaceted intervention on number of antimicrobial prescriptions for suspected urinary tract infections in residents of nursing homes: cluster randomised controlled trial. BMJ; 331:669. http://www.bmj.com/content/331/7518/669.

McMurdo, M.E. and Gillespie, N.D. (2000) Urinary tract infection in old age: over-diagnosed and over-treated. Age and Ageing. 29 (4) 297-8

Nicolle,L.E., Bjornson,J., Harding,G.K.M. & MacDonell,J.A (1983) Bacteriuria in Elderly Institutionalized Men. New England Journal of Medicine. 309:1420-1425.

Orr,P.H., Nicolle,L.E., Duckworth,H., Brunka,J., Kennedy,J., Murray,D & Harding,G.K. (1996) Febrile urinary infection in the institutionalised elderly. American Journal of Medicine.100 71-77.

Scottish Antimicrobial Prescribing Group (2013). Decision aid for diagnosis and management of suspected urinary tract infection in older people. NHS Scotland. www.sign.ac.uk/pdf/sign88_algorithm_older.pdf

8 thoughts on “Urine – to dip or not?

  1. Peter says:

    Bacteraemia?

    ” ..dry tongue and reduced skin”

    Clarify please…

  2. rob fenwick says:

    Apologies – should have read “….dry tongue and reduced skin turgor”. Now amended. Thanks.

  3. Anonymous says:

    great thanks

  4. Tanya says:

    I have seen a reduced use of dip stick testing in aged care, unless symptoms are present, which is good. This article is a great source.

  5. Anonymous says:

    Please solve argument can you smell a UTI.

  6. rob fenwick says:

    Good question!

    The paper below would suggest that smell is “not predictive of a laboratory confirmed UTI”

    https://www.ncbi.nlm.nih.gov/pubmed/20594439

  7. James Nottle says:

    Surely bacteriuria rather than bacteraemia, no dip would have any predictive value for that. ASB is not only common, but the quality of sample submitted is also often poor . That said, I imagine a dip will have a decent NPV so there some value in it, so long as you understand the limitations of the test.

    A quick, POCT for LPS (major antigenic element of gram negative bacteria) from blood could be very useful, but not sure that is the direction of travel for diagnostics going forward

  8. rob fenwick says:

    Thanks James!

    Correct on the bacteriuria (amended). In your experience of the poor sample quality, is this limited to “MSU” or “CSU” samples (or both)?

    I have linked to an article from a few years ago that tabulates the sensitivity, specificity, PPV and NPV of urinalysis for interest. The range of values does add to the confusion somewhat though… e.g. NPV ranging from 70-88% (table 2 – http://www.aafp.org/afp/2005/0315/p1153.html)

    I personally think identification based upon the clinical of symptoms suggestive of UTI, coupled with urinalysis, offers a safe and cost effective approach to this group. I’m not aware of any emergency departments currently using LPS testing, or whether there have been any trials comparing its use against standard care. In my mind, whilst it may provide diagnostic benefit for the clinician/ hospital, it would be important to see if this directly resulted in any patient-centred benefit prior to adoption.

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