About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Lower UTI (cystitis): dysuria, frequency, urgency, suprapubic pain. Upper UTI (pyelonephritis): systemic symptoms + loin pain + fever
- E. coli causes ~80% of UTIs. Other organisms: Klebsiella, Proteus (associated with staghorn calculi), Staphylococcus saprophyticus (young women)
- Diagnosis in women <65: ≥2 key urinary symptoms + no vaginal discharge/irritation → treat empirically without urine culture
- First-line antibiotic for uncomplicated lower UTI in women: nitrofurantoin 100 mg MR BD for 3 days
- Always send urine culture in: men, pregnant women, children, recurrent UTIs, treatment failure, catheterised patients
Overview
Urinary tract infections are bacterial infections affecting the lower (cystitis — bladder) or upper (pyelonephritis — kidney) urinary tract. They are classified as uncomplicated (normal urinary tract, non-pregnant woman) or complicated (abnormal urinary tract, male, pregnant, catheterised, immunocompromised). The primary route of infection is ascending — bacteria colonise the periurethral area and ascend via the urethra to the bladder. The shorter female urethra explains the much higher incidence in women. Risk factors include female sex, sexual activity, pregnancy, menopause (oestrogen deficiency), urinary tract abnormalities, catheterisation, diabetes, and immunosuppression.
Epidemiology
UTIs are the commonest bacterial infection in women. Approximately 50% of women experience at least one UTI in their lifetime, with 25% experiencing recurrence. Annual incidence in adult women is approximately 10–15%. UTIs in men are uncommon before age 50 and should prompt investigation for underlying urological abnormality. UTIs account for approximately 1–3% of GP consultations. Catheter-associated UTIs (CAUTIs) are the most common healthcare-associated infection.
Clinical Features
Symptoms
Dysuria (burning or stinging on urination)
Urinary frequency and urgency
Suprapubic pain or discomfort
Cloudy or malodorous urine
Haematuria (visible or non-visible)
Nocturia
Systemic symptoms: fever, rigors, loin pain, nausea/vomiting (suggests pyelonephritis)
Confusion in elderly (UTI is a common cause but do not treat asymptomatic bacteriuria for confusion alone)
Signs
Suprapubic tenderness
Usually no abnormal signs in uncomplicated lower UTI
Renal angle tenderness (pyelonephritis)
Fever and tachycardia (systemic infection)
Vaginal discharge (suggests alternative diagnosis — exclude before diagnosing UTI)
Investigations
First-line
Urine dipstickNitrites (most specific — bacterial conversion of nitrates) and leucocyte esterase (sensitive but less specific). Positive nitrites + leucocytes = high probability of UTI
Clinical assessmentIn women <65 with ≥2 key urinary symptoms and no vaginal symptoms → can treat empirically without dipstick or culture (NICE NG109)
Second-line
Midstream urine (MSU) for MC&SSend in: all men, pregnant women, children, recurrent UTIs, treatment failure, atypical symptoms, catheterised patients. Significant bacteriuria: ≥10⁵ CFU/mL
BloodsFBC, CRP, U&Es — if systemic illness, pyelonephritis, or sepsis suspected
Specialist
Renal tract USSIf recurrent UTIs in men, children, or women with atypical features — exclude structural abnormality, obstruction, or stones
Urology referralMen with UTI (always investigate), recurrent complicated UTIs, haematuria after infection resolved
1
Uncomplicated lower UTI in non-pregnant women
- First-line: nitrofurantoin 100 mg MR BD for 3 days (if eGFR ≥45)
- Second-line: trimethoprim 200 mg BD for 3 days (if low local resistance rates)
- Third-line (based on culture): pivmecillinam 400 mg TDS for 3 days, or fosfomycin 3 g single dose
- Advise adequate fluid intake, paracetamol/ibuprofen for pain
2
UTI in men
- Always send MSU for culture before starting treatment
- Trimethoprim 200 mg BD for 7 days (first-line) or nitrofurantoin 100 mg MR BD for 7 days
- Longer course (7 days) than in women — higher risk of prostatitis/complicated infection
- Investigate all UTIs in men: consider renal tract USS, PSA (after infection resolves), urology referral
3
UTI in pregnancy
- Always send MSU — screen and treat asymptomatic bacteriuria in pregnancy (reduces pyelonephritis risk)
- First-line: nitrofurantoin 100 mg MR BD for 7 days (avoid near term — theoretical neonatal haemolysis)
- Avoid trimethoprim in first trimester (folate antagonist — teratogenic risk)
- Refer for investigation if recurrent
4
Recurrent UTIs (≥2 in 6 months or ≥3 in 12 months)
- Behavioural advice: adequate hydration, post-coital voiding, avoiding constipation
- Consider vaginal oestrogen in postmenopausal women
- Methenamine hippurate (urinary antiseptic) — NICE NG112 recommended as alternative to prophylactic antibiotics
- Single-dose antibiotic post-coitally if related to sexual activity
- Daily low-dose prophylactic antibiotics if other measures fail (e.g. nitrofurantoin 50–100 mg ON for 6 months)
Complications
- Pyelonephritis: Ascending infection to kidneys — can cause sepsis and AKI
- Urosepsis: Life-threatening systemic response — Sepsis 6 management
- Renal abscess: From complicated or untreated pyelonephritis
- Preterm labour: UTI/asymptomatic bacteriuria in pregnancy increases preterm delivery risk
- Recurrence: ~25% of women with one UTI will have recurrent infections
UKMLA Exam Tips
- 1Nitrites on dipstick = bacteria present (specific). Leucocytes alone = non-specific (also positive in vaginal contamination)
- 2Do NOT treat asymptomatic bacteriuria EXCEPT in pregnancy (screen at booking and treat to prevent pyelonephritis)
- 3Nitrofurantoin: NOT effective if eGFR <45 mL/min (inadequate concentration in urine). Use alternative
- 4Proteus mirabilis → urease-producing → alkaline urine → struvite (staghorn) calculi
- 5Dipstick testing should NOT be used in adults >65 (high false positive rate) or catheterised patients — use clinical assessment
- 6UTI in men is ALWAYS complicated — requires investigation (never dismiss as simple cystitis)
- 7Trimethoprim: avoid in first trimester of pregnancy (folate antagonist) and in patients on methotrexate
practicetest your knowledge on utiApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — renal and beyond.
open q-bank