Standard dipstick tests for UTI miss over 60% of infections
GPs rely on dipstick tests to diagnose UTIs. But these tests are seriously flawed. Research shows dipsticks have a 70% inaccuracy rate (see also here) causing some to suggest it should be abandoned as a diagnostic tool. New research found that dipstick tests miss at least 60% of infections in patients with persistent or chronic infections.
Relying on flawed tests have serious consequences for patients. When dipstick tests fail to identify an infection, doctors and urologists can dismiss bacterial infection and look for other causes. With an infection ruled out, patients often then undergo painful and invasive investigations to find another cause.
How do dipstick tests work?
GP analysis of a urine sample involves a dipstick test before any urine laboratory analysis is carried out. A standard urine test strip may comprise up to 10 different chemical pads which react (change colour) when immersed in, and then removed from, a urine sample. The test can often be read in as little as 1-2 minutes after dipping, although some tests require longer.
The analysis includes testing for the presence of proteins, blood, nitrites and leukocytes (white blood cells), all symptoms of urinary tract infections. Urine dipsticks were first developed for commercial use in the late 50s/early 60s.
What are the problems with dipstick tests?
Negative dipstick analysis is common even though the patient has described UTI symptoms. This can be due to the following:
- The use of any existing antibiotics will reduce bacterial growth leading to no evidence of infection on dip
- Drinking too much liquid before providing a sample thus diluting it.
- The dipsticks are calibrated to detect white blood cells counts of >10 5 (100,000) bacteria per millilitre of urine or greater. For someone with a bacterial infections lower than this cut off range, the dipstick will report a false negative.
- Bacteria require a minimum of four hours to reduce the nitrate in urine to nitrites. Not all bacteria responsible for UTIs contain nitrite reductase, the enzyme responsible for this conversion. Examples of Nitrite reducing bacteria including E-coli, Proteus and Klebsiella. But if your infection is caused by Enterococcus or Pseudomonas, this enzyme conversion will not occur.
- Various chemicals can also interfere with urine dipstick analysis. Some chemicals that may cause false-negative results include ascorbic acid (such as vitamin C) and oxalic acid (an organic compound found in many plants such as leafy greens, vegetables, fruits, cocoa, nuts and seeds).
- Biofilm or embedded bladder wall infections mean that the bacteria are embedded and hidden away from the urine, not floating in it. When you urinate, the bacteria will not transfer into the sample pot resulting in lack of detection on a dipstick.
Research in the last 20 years has shown that whilst they can identify acute infections, it is low growth bacterial infections where they become unreliable. One study noted: “The nitrite test performs particularly badly and leukocyte esterase achieved a sensitivity of only 59%”.1, 2
What to avoid if you need to provide a urine sample:
- Dilution of the sample by drinking too much liquid (the first urination of the day when you wake up or acidic, concentrated urine is best for analysis). If this is not possible, limit fluids for around three – four hours before providing your sample so it isn’t too dilute.
- Usage of previous antibiotics to treat a recent infection. Ideally you need to be off antibiotics for around 7-10 days to clear the medication from your system before providing another urine sample. Usage of antibiotics may inhibit bacterial growth resulting in a negative result even if you still have symptoms.
- If you are using D-Mannose or other natural herbal supplements to treat your infections stop at least 48 hours before testing.
- Urinary painkillers such as Azo should be stopped 24 hours before a sample as this medication type can affect results.
- Diuretics should also be stopped as well as Vitamin C – all can lead to false negative results.