A dipstick goes into a urine sample, changes colour, and produces a row of results in under a minute. It’s one of the cheapest urinalysis tests in medicine.
It’s also frequently over-read. The test is genuinely good at one job and genuinely poor at another, and knowing which is which changes how a result should land.
First, a note: this explains what the parameters mean. Interpretation belongs with a clinician.
The two infection markers
Most of what people want from a urinalysis comes down to two squares on the strip.
Leukocyte esterase detects an enzyme released by white blood cells. A positive result correlates well with pyuria — white cells in the urine[5]. It tells you inflammation is present, not what caused it.
Nitrite works indirectly. Dietary nitrate appears in urine, and certain gram-negative bacteria — *E. coli* and *Klebsiella* among them — convert it to nitrite[5]. Detecting nitrite therefore implies bacteria capable of that conversion.
That indirect mechanism creates a specific vulnerability. Not all bacteria reduce nitrate. If the organism can’t perform the conversion, the square stays negative no matter how many bacteria are present.
Other reasons nitrite comes back falsely negative: insufficient dietary nitrate, dilute urine, or urine that hasn’t sat in the bladder long enough for conversion to occur[2].
Good at ruling out, poor at ruling in
Here’s the asymmetry, with numbers.
A 2025 systematic review and meta-analysis pooled 16 studies of dipstick testing in older adults. For predicting bacteriuria, the pooled figures were sensitivity 90% (84–94%) and specificity 56% (43–68%)[1].
In symptomatic older adults specifically, predicting UTI: sensitivity 92%, specificity 39% (19–62%)[1].
Read those together. High sensitivity means few true cases are missed — so two negative squares are informative. Low specificity means many positives aren’t what they appear — so a positive square is not.
The authors state it directly: a positive dipstick result is inconclusive and does not confirm bacteriuria or UTI in symptomatic older adults[1].
Individual markers perform worse still. In one study of 635 culture-positive patients, sensitivity was 23.3% for nitrite alone and 48.5% for leukocyte esterase alone[2]. Nitrite missed roughly three-quarters of confirmed infections.
Nitrite’s profile is lopsided in a useful way: positive predictive value around 95%, negative predictive value 25–70%[5]. A positive nitrite strongly suggests infection. A negative one excludes very little.
Why a positive result isn’t a prescription
This is the part I had wrong.
I assumed a positive urine test meant infection, and infection meant treatment. Neither step holds automatically.
Asymptomatic bacteriuria — bacteria present in urine without symptoms — is common, and becomes more common with age. The 2025 review notes that because of its high prevalence in older individuals, bacteriuria alone lacks diagnostic value[1].
A supporting figure: in a study across 32 nursing homes, 32% of urine cultures from 651 residents grew a potentially pathogenic bacterium[3]. Roughly a third, in a population not selected for having symptoms.
If a third of samples grow bacteria at baseline, finding bacteria in any one sample tells you considerably less than it seems to.
The picture shifts when infection is severe. In hospitalised patients aged 65 and over with bacteraemic UTI — the same organism confirmed in both blood and urine — dipstick sensitivity reached 96.9%, though the false positive rate among culture-negative patients was 42.4%[4]. High sensitivity in serious illness, alongside the same specificity problem.
This is why symptoms matter as much as the strip. A positive result in someone with burning, urgency and frequency means something different from the same result in someone with no complaints at all.
What makes results wrong
Worth knowing when a result surprises you.
| Marker | False negative | False positive |
| Nitrite | Non-nitrate-reducing bacteria; low dietary nitrate; dilute urine; short bladder dwell time | Uncommon |
| Leukocyte esterase | Recent antibiotics; glycosuria; proteinuria; high specific gravity; low bacterial count | Contaminated specimen; some infections other than bacterial |
[Table 1] Common sources of false results · Source: Summary of related literature[2][5]
Recent antibiotics deserve emphasis. If you’ve taken antibiotics in the days before testing, the strip may read negative regardless of what’s happening.
Collection technique matters for the opposite reason. A contaminated sample can produce a positive that reflects the collection, not the bladder.
The rest of the strip
The infection markers get the attention, but the strip reports more.
Protein — a screening marker for kidney function, which we covered in the context of Korea’s national health screening panel. Transient elevations occur with fever, exercise and standing for long periods.
Glucose — normally absent. Its presence usually reflects blood glucose exceeding the kidney’s reabsorption threshold.
Blood — the highest single-marker sensitivity in one study at 63.9% in culture-positive patients[2], though blood in urine has many causes besides infection and always warrants explanation rather than assumption.
Specific gravity and pH — concentration and acidity, which affect how the other squares perform. Very dilute urine can weaken several readings at once.
If you’re in Korea
Two practical notes.
Urine protein is part of the national health screening panel, as covered earlier in this series. So many people here receive a urinalysis result annually without having sought one — and that result is a screening finding, not a diagnosis.
A positive finding on screening warrants follow-up, not self-treatment. Korea’s screening programme includes follow-up consultation for several abnormal findings. That consultation is where a positive square gets sorted into “needs a culture,” “needs repeating,” or “needs nothing.”
And a point relevant to this category: if you experience recurrent urinary symptoms, the useful question is what’s driving the recurrence. As covered in the cranberry posts, prevention and treatment are separate matters, and after menopause tissue changes can be part of the picture — which changes the approach entirely.
Closing
The dipstick is a rule-out test that gets used as a rule-in test.
Sensitivity around 90% and specificity around 56% describes an instrument that is trustworthy when it says no and much less so when it says yes. Add the fact that a third of samples in one older population grew bacteria without symptoms, and a single positive square stops looking like an answer.
What I’d been doing was treating one line on a printout as a diagnosis. It isn’t — it’s one input, and the most important other input is whether anything actually feels wrong.
Next in this series: what changes in urogenital tissue after menopause.
At a Glance
- Leukocyte esterase detects white-cell activity; nitrite detects bacteria that convert dietary nitrate
- Not all bacteria reduce nitrate — a negative nitrite does not exclude infection
- Pooled performance in older adults: sensitivity 90%, specificity 56%; in symptomatic older adults, specificity 39%
- A positive dipstick is described as inconclusive for confirming UTI in symptomatic older adults
- Individually: nitrite sensitivity 3%, leukocyte esterase 48.5% in culture-positive patients
- Nitrite’s PPV ~95%, NPV 25–70% — positive suggests strongly, negative excludes little
- 32% of nursing home residents’ cultures grew pathogenic bacteria without selection for symptoms
- Recent antibiotics, dilute urine and glycosuria can all produce false negatives
※ This article explains what urinalysis parameters measure and is for general information only. It does not replace medical diagnosis or treatment. A screening result is not a diagnosis, and neither a positive nor a negative dipstick should be acted on without clinical assessment. Do not self-treat urinary symptoms — burning, blood in the urine, fever or flank pain warrant prompt medical attention.
References
- “Accuracy of leukocyte esterase and nitrite tests for diagnosing bacteriuria in older adults: a systematic review and meta-analysis”, Clinical Microbiology and Infection, https://www.clinicalmicrobiologyandinfection.org/article/S1198-743X(25)00425-2/fulltext
- “Reliability of dipstick assay in predicting urinary tract infection”, Journal of Family Medicine and Primary Care (individual marker sensitivities; false negative causes), https://journals.lww.com/jfmpc/fulltext/2015/04020/reliability_of_dipstick_assay_in_predicting.22.aspx
- “Evaluation of dipstick analysis among elderly residents to detect bacteriuria: a cross-sectional study in 32 nursing homes”, PMC, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2724370/
- “Sensitivity of the dipstick in detecting bacteremic urinary tract infections in elderly hospitalized patients”, PMC, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5663520/
- “Dipstick urinalysis”, LITFL Critical Care Compendium (marker mechanisms, predictive values, interference sources), https://litfl.com/dipstick-urinalysis/