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I have completed bits of my EM training from India. Currently I am boarded with credentials from Christian Medical College, Vellore and also from the prestigious Royal College of Emergency Medicine, UK.  I am currently working in London as an A&E doctor, trying to appreciate the differences in the practise and culture of Emergency Medicine across different healthcare systems. I have always been an avid FOAMed supporter because FOAMed played an indispensable role during the days of my initial training. Through this blog, I aspire to disseminate knowledge and stay up to date with the EM literature. 

Monday, August 14, 2017

Overtesting and Misinterpretation - Urine Dip Pearls

Interpreting lab tests requires a considerable amount of knowledge and experience. One such test is urine dipstick which is often done in the ED to look for blood, evidence of infection, ketones etc. Since Emergency Departments across the globe are working under tremendous amount of time constraints, tests are now being done based of chief complaints (abdomen pain panel, pleuritic CP panel, Headache panel etc.) instead of clinical suspicion of a diagnosis. While this reduces the time to reach a conclusion, it makes evaluation and medical decision making very complex for a clinician. 

What are we supposed to do with a result that we never expected and we never wanted that to be sent at the first place? Positive hstroponin in a very low risk patient, positive d-dimer in a 16 year old who was hyperventilating or a positive urine dip for nitrites in an asymptomatic patient.





We know that we are overdiagnosing and over-treating UTIs. Rates of Misdiagnosis of UTI are up to 40%. Therefore, it is imperative to have have a pre-test probability before we order a urine dip or microscopy. And if it is already reported before you have actually seen the patient, be comfortable in disregarding the results if it does fit in the clinical scenario. 

Having a clinical questions can help. Ask yourself these two questions before you order any test (not just Urine Dip):

1.What are you looking for in the test. Is it Nitrites or blood or ketones? 
2. What is going to be your next step if the result is positive or negative?



Putting Urine Dip into a clinical context differentiates a clinician from other healthcare providers. Treating positive urine nitrites for UTI - Anyone can do that! 
But Medicine is not that simple!


Key points while interpreting a urine dip:

1. Bacteriuria does not equal UTI
If you send a culture on asymptomatic bacteriuria, you might get a positive culture but what if your patient never had any symptoms? The answer is - do not bother sending urine for testing in asymptomatic patients and do not treat asymptomatic bacteriuria (exceptions - Rx in pregnancy in those who are undergoing a urologic procedure). UTI is a clinical diagnosis, not a lab diagnosis. Colony counts and cultures are pointless without symptoms or clinical suspicion. 

2. Leucocyte Esterase (LE) is indicative of pyuria not UTI
Here is a list of things than can cause pyuria:
  • HIV
  • STDs
  • Appendicitis
  • Urolithiasis
  • Malignancy
  • Nephritis 
  • Dehydration
  • Diverticulitis
  • Indwelling catheters
Once again, results for LE needs to interpreted with a clinical context. In neutropenic patients, urine WBCs may be artificially low despite an infection

3. Nitrites 
Nitrates in the urine are converted to nitrites in the presence of Gram-negative bacteria such as E.coli. A positive nitrite test is a indirect marker of bacteriuria, not always a marker of infection (unless patient is symptomatic).

Nitrites are not produced by S. saprophyticus, Pseudomonas or enterococci, so a negative nitrites does NOT rule out UTI. Also watch your method of sample collection. Almost universally, urine is collected in a non-sterile fashion and thus interpretation should be always in the clinical context. Presence of Epithelial cells indicate a contaminated sample. 


Negative leukocyte esterase and nitrite negative almost rules out UTI


4. Elderly with Altered Mental State and UTI - Not always!
UTI is this scenario is pretty much a diagnosis of exclusion (Rule out Neuro and GI causes before labelling as UTI). Asymptomatic bacteriuria is extremely common in elderly. Rx them based on the history of symptoms and confirm your diagnose with a catheterised sample. When history is compromised due to cognitive issues - Look for fever, chills, elevated WCC, CRP, previous episodes of UTI to gauge your suspicion. If the look stable (normotensive, not tachycardia, no fever) then it is reasonable to hold Abx and convey this to the in-patient teams. 

5. He smells of urine, so we think it is a UTI
Anyone who is unkempt, not looked after well and urinates in his pants is going to smell bad. Bad smell is not always an indicator of Urine Infection. Do not prematurely close the diagnosis here. Smell can be affected by a number of factors such a your hydration status, concentration of urea, diet. Do a complete history and physical and then come to a conclusion. 



Take Home
  • Do not treat asymptomatic bacteriuria
  • Hold Abx if they look stable. Liaise with in-patient teams. 
  • Negative leukocyte esterase and nitrite negative makes UTI highly unlikely

References:

Schulz L, Hoffman RJ, Pothof J, et al. Top ten myths regarding the diagnosis and treatment of urinary tract infections. J Emerg Med. 2016 Jul; 51(1): 25-30. 


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     Lakshay Chanana
     
     Speciality Doctor
     Northwick Park Hospital
     Department of Emergency Medicine
     England

     @EMDidactic


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