Factors affecting the accuracy of dipsticks and thus diagnosis of a UTI based on the guidelines above may include:

• 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). GPs fail to advise patients to wait at least four hours before providing a sample.
• 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. This is because the continuation of the medication in your system may inhibit bacterial growth even if you still have symptoms.
• Certain bacterial strains not producing nitrate reductase which converts urinary nitrates to nitrite – as noted above this is a key part of the dipstick analysis to determine a UTI.
• Various chemicals may also interfere with urine dipstick analysis producing a false negative result. These include ascorbic acid (such as vitamin C) and oxalic acid (an organic compound found in many plants including leafy greens, vegetables, fruits, cocoa, nuts and seeds).
• Biofilm or embedded bladder wall infections mean that the bacteria are hidden away from the urine, not floating in it. Thus when you urinate, the bacteria will not transfer into the sample pot meaning they cannot be detected on a dipstick.