Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Vaginal discharge differential diagnosis
Obstetrics and gynaecology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Discharge can accompany time-critical disease
Haemodynamic disturbance, pregnancy with pain or bleeding, severe pelvic tenderness, fever, peritonism, rapidly spreading vulval inflammation or toxic shock features require urgent assessment rather than a routine vaginitis pathway.
Action: Check observations and pregnancy status, assess abdominal and pelvic red flags, begin sepsis or ectopic-pregnancy escalation where indicated, and involve acute gynaecology or emergency care without waiting for routine swab results.
Overview
Distinguish physiological discharge from vaginal, cervical, upper-genital-tract and non-infective disease while recognising pregnancy complications, pelvic infection, safeguarding concerns and malignancy promptly.
Vaginal discharge is a symptom with anatomical and physiological context. Establish what has changed from the person's normal pattern: onset, volume, colour, consistency, odour, cycle timing and association with itching, dysuria, dyspareunia, pelvic pain, fever, bleeding or vulval lesions. Ask about pregnancy possibility, last menstrual period, contraception, recent antibiotics, diabetes, immunosuppression, douching, intravaginal products and a possible retained tampon or other foreign body. Use neutral language and offer privacy for sexual and safeguarding history.
The first useful distinction is physiological versus pathological, followed by the likely site. Clear or white fluctuating discharge without irritation may be physiological leucorrhoea. Vulvovaginal inflammation produces itch, burning, superficial dyspareunia and erythema. Cervicitis can produce mucopurulent discharge, intermenstrual or postcoital bleeding and a friable cervix, yet chlamydia and gonorrhoea are frequently asymptomatic. Upper-tract infection should be considered when lower abdominal pain, deep dyspareunia, abnormal bleeding or tenderness accompanies discharge.
Practice
Two practice questions
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Question 1 of 2
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Obstetrics and gynaecologyOriginal SBA
Interpreting a discharge phenotype
A 31-year-old has thin grey-white discharge with a fishy odour, little vulval inflammation and a vaginal pH of 5.2. Which diagnosis best fits this pattern?
Sources and review status6 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.
The vaginal ecosystem helps discriminate common causes but does not replace testing. Lactobacillus-associated acidity is usually retained in candidiasis, whereas bacterial vaginosis and trichomoniasis commonly raise pH above 4.5. Thin grey-white discharge and odour favour bacterial vaginosis; frothy yellow-green discharge, vulvitis and a strawberry cervix can occur with trichomoniasis but are neither necessary nor sufficiently specific. Thick curdy discharge can occur with candidiasis, although severe pruritus and vulval signs are often more useful than texture.
Examination is guided by consent, age, symptoms and what the result will change. Begin with observations, abdominal assessment and external inspection. A speculum examination can identify cervical discharge, contact bleeding, a foreign body, vaginal atrophy or lesions, but should not be forced and is not automatically required for self-taken NAAT. A bimanual examination is appropriate when pelvic inflammatory disease is possible. Offer a chaperone, explain each step, stop when requested and use a trauma-informed approach when assault or coercion may be relevant.
Choose tests that answer the differential. A self-taken vulvovaginal swab is a sensitive genital specimen for chlamydia NAAT; gonorrhoea NAAT should be supplemented by culture before treatment where possible, especially when infection is suspected. Microscopy, Gram stain or validated molecular testing can support candidiasis, bacterial vaginosis and trichomoniasis. Test extragenital sites according to exposure, not identity. Pregnancy testing changes both urgency and medicine choices. Ulcers require lesion HSV NAAT and syphilis serology rather than a generic discharge swab.
Close the consultation by separating immediate care, pending results and safety-netting. Treat a supported syndrome, arrange partner management for diagnosed sexually transmitted infection, and explain abstinence advice accurately for the organism and regimen. If initial results are negative, reconsider non-infective vulval disease, desquamative inflammatory vaginitis where specialist assessment supports it, urinary or bowel fistula, genital tract cancer and pain syndromes. Persistent bleeding, constitutional symptoms or examination abnormalities justify escalation even when infection testing is reassuring.
Key points
Normal discharge varies with ovulation, pregnancy, sexual arousal and exogenous hormones; it is usually clear or white and is not accompanied by itch, strong odour, bleeding or pelvic pain.
Localise the syndrome before naming an organism: vulval itch and soreness suggest candidiasis or dermatosis, malodour suggests bacterial vaginosis or trichomoniasis, and mucopurulent contact bleeding suggests cervicitis.
Bacterial vaginosis typically causes thin homogeneous discharge, a fishy odour and vaginal pH above 4.5 with little inflammation; symptoms alone do not prove the diagnosis.
Vulvovaginal candidiasis more often causes itch, soreness, erythema, fissuring and non-offensive discharge with pH at or below 4.5; asymptomatic Candida colonisation does not require treatment.
Take an exposure-sensitive sexual history and offer site-appropriate NAAT for chlamydia and gonorrhoea; add a validated trichomonas test when the phenotype or exposure makes it plausible.
Pregnancy testing, consented examination and targeted microscopy, pH or swabs are selected according to symptoms; a normal external examination does not exclude cervical or upper-tract infection.
Persistent or recurrent discharge after negative infection tests should trigger review for irritant dermatitis, a retained foreign body, genitourinary syndrome of menopause, fistula or neoplasia rather than repeated empirical antimicrobials.
Aetiology
01
Physiological secretion
Cervical mucus and transudate vary with ovulation, pregnancy, arousal and hormonal medication without causing inflammation, malodour or tissue damage.
02
Infection or dysbiosis
Candida inflammation, bacterial vaginosis, trichomoniasis and cervical sexually transmitted infections alter discharge through different ecological and inflammatory mechanisms.
03
Non-infective pathology
Irritant exposure, dermatosis, oestrogen deficiency, retained material, fistula and genital tract neoplasia can all produce discharge or perceived wetness.
Pathophysiology
1
Microbiome disruption
Loss of lactobacillus dominance permits anaerobic overgrowth, raises vaginal pH and produces volatile amines responsible for bacterial-vaginosis odour.
2
Mucosal inflammation
Candida invasion, protozoal infection or chemical irritation activates local inflammation, leading to soreness, erythema, oedema and altered secretions.
3
Cervical exudation
Endocervical infection recruits inflammatory cells and mucus, causing mucopus, friability and contact bleeding that may be mistaken for vaginitis.
4
Upper-tract ascent
Organisms can ascend through the cervix to the endometrium and tubes, producing pelvic pain and inflammation even when lower-tract testing is negative.
Clinical features and red flags
Physiological leucorrhoea
Clear or white non-offensive discharge that varies with the cycle or pregnancy and causes no itch, pain, bleeding or examination abnormality is often physiological.
Vaginal dysbiosis pattern
Thin homogeneous malodorous discharge, minimal vulval inflammation and pH above 4.5 support bacterial vaginosis when confirmed with Amsel or laboratory criteria.
Inflammatory vulvovaginitis
Marked itch, soreness, erythema, oedema or fissuring points toward candidiasis, trichomoniasis, irritant disease or dermatosis rather than uncomplicated bacterial vaginosis.
Cervical or upper-tract disease
Mucopus, contact bleeding, lower abdominal pain, deep dyspareunia or cervical and adnexal tenderness should prompt STI testing and assessment for pelvic inflammatory disease.
Non-infective persistence
Repeated negative microbiology with visible skin change, dryness, foreign-body history, blood staining or urinary or faecal leakage redirects evaluation beyond recurrent infection.
Red flags requiring action
A positive pregnancy test with unilateral pain, shoulder-tip pain, bleeding, syncope or peritoneal signs requires urgent assessment for ectopic pregnancy.
Fever, vomiting, marked lower abdominal pain, cervical excitation, adnexal tenderness or peritonism suggests pelvic inflammatory disease or a surgical emergency.
Investigations
01Urine or serum hCGFirst step
Why
Identify pregnancy before interpreting pain, bleeding or selecting medicines.
Interpretation and limitations
A positive result with pain, bleeding or instability requires urgent pregnancy localisation; a negative test does not explain discharge and the remaining differential still needs assessment.
02Vulvovaginal and exposure-site NAAT
Why
Detect chlamydia, gonorrhoea and trichomoniasis with specimens matched to sexual exposure.
Interpretation and limitations
A positive result supports organism-specific treatment and partner notification; a negative genital sample does not exclude infection at an untested rectal or pharyngeal site.
03Vaginal pH, microscopy or Gram stain
Why
Differentiate bacterial vaginosis, Candida-associated inflammation and trichomoniasis when locally available.
Interpretation and limitations
pH above 4.5 supports bacterial vaginosis or trichomoniasis but is nonspecific; yeast on microscopy matters only when compatible symptoms are present.
04Gonococcal culture and susceptibility
Why
Confirm viable gonorrhoea and guide antimicrobial selection amid resistance.
Interpretation and limitations
Obtain culture before antibiotics whenever feasible; a negative culture after a positive NAAT may reflect lower sensitivity and should be reconciled with timing and site.
Differential diagnosis
01
Vaginal infection
Bacterial vaginosis, candidiasis and trichomoniasis overlap in appearance but differ in inflammation, pH, microscopy, recurrence pattern and partner implications.
02
Cervicitis or PID
Chlamydia or gonorrhoea may produce cervical discharge, bleeding and upper-tract tenderness, or may remain clinically silent despite transmissibility.
03
Dermatosis or atrophy
Contact dermatitis, lichen disorders and genitourinary syndrome of menopause cause irritation, dryness, fissuring and secondary secretion without primary infection.
04
Foreign body or fistula
A retained tampon causes offensive discharge, while continuous watery, urinary or faecal leakage suggests a tract requiring structural assessment.
05
Genital tract neoplasia
Persistent blood-stained or watery discharge with postcoital bleeding, visible abnormality, pelvic mass or postmenopausal onset needs urgent exclusion of cancer.
Management
01TriageExclude pregnancy and severe infectionFirst stepDischarge is accompanied by pain, bleeding, fever, systemic symptoms or clinical deterioration.+
1Record observations, assess abdomen and obtain hCG promptly when pregnancy is possible.
3When PID is clinically likely, collect appropriate microbiology but do not delay empirical treatment for laboratory confirmation.
02LocalisationMatch phenotype to anatomical siteThe patient is stable and requires a focused diagnostic assessment.+
1Separate physiological variation from vulval inflammation, vaginal dysbiosis, cervicitis, upper-tract disease and a non-infective structural cause.
Complications
01
Ascending pelvic infection
Untreated cervical infection may progress to endometritis, salpingitis, abscess, chronic pelvic pain, ectopic pregnancy and tubal-factor infertility.
02
Ongoing transmission
Missed sexually transmitted infection permits asymptomatic spread and reinfection when partners are neither notified, tested nor treated appropriately.
03
Diagnostic delay
Repeated empirical vaginitis treatment can postpone recognition of dermatosis, retained foreign body, genital tract malignancy or a fistula.
04
Treatment-related harm
Unnecessary antimicrobials cause adverse effects, selection pressure and further ecological disruption while reinforcing an incorrect recurrent-infection label.
Monitoring and follow-up
Confirm how and when microbiology and pregnancy results will be communicated, including a confidential contact method and action for positive findings.
Review unresolved symptoms after treatment to distinguish non-adherence, reinfection, resistance, an alternative infection and a non-infective diagnosis.
Ask specifically about new pelvic pain, fever, vomiting, bleeding, pregnancy symptoms or urinary retention and provide a same-day escalation route.
Reassess persistent contact bleeding, postmenopausal discharge or visible vulval and cervical abnormalities even if initial STI tests are negative.
Document partner-notification completion and disease-specific retesting without labelling every follow-up sample a test of cure.
Special situations
Discharge texture is not a test
Descriptions such as curdy or frothy can guide hypotheses, but overlapping appearances make symptom-only antimicrobial prescribing unreliable.
Inflammation changes the differential
Prominent erythema, fissuring and itch are discordant with uncomplicated bacterial vaginosis and should prompt Candida, trichomonas, dermatitis and dermatosis assessment.
Specimen site follows exposure
A vulvovaginal NAAT answers genital exposure but does not assess an exposed rectum or pharynx; testing should be anatomically complete and non-judgemental.
Negative swabs are useful
When appropriately timed tests are repeatedly negative, that evidence should redirect assessment toward skin disease, hormonal atrophy, pain syndromes or structural pathology.
Bleeding deserves its own pathway
Postcoital, intermenstrual and postmenopausal bleeding may coexist with discharge but require cervical, pregnancy and cancer-focused assessment beyond vaginitis testing.
Common pitfalls
01
Treating any white discharge as candidiasis without documenting itch, inflammation or microbiological support in recurrent disease.
02
Assuming odour proves bacterial vaginosis while overlooking a retained tampon, trichomoniasis or foreign-body infection.
03
Using one genital NAAT to imply that all exposed anatomical sites have been tested.
04
Allowing negative lower-tract tests or a normal ultrasound to exclude clinically suspected pelvic inflammatory disease.
05
Repeating antimicrobials for persistent symptoms without inspecting the vulva and considering atrophy, dermatosis, malignancy or chronic pain.
06
Performing an intimate examination without explicit consent, explanation, chaperone discussion and the person's control over stopping.
Hypotension, tachycardia, rash, confusion, severe myalgia or a retained tampon raises concern for toxic shock or sepsis and needs emergency care.
Postmenopausal, persistent blood-stained, offensive or watery discharge, especially with a visible lesion or pelvic mass, needs an expedited cancer pathway.
Severe vulval pain, necrosis, rapidly extending erythema, urinary retention or immunosuppression warrants same-day specialist examination.
05
Targeted cervical, endometrial or imaging assessment
Why
Investigate persistent bleeding, mass, suspected fistula, foreign body or upper-tract pathology.
Interpretation and limitations
An abnormal cervix, endometrial risk or postmenopausal blood-stained discharge warrants referral; ultrasound may show abscess or mass but cannot rule out uncomplicated PID.
2
Offer consented external, speculum or bimanual examination only where findings will alter the pathway, with a chaperone and option to stop.
3Select pregnancy, pH, microscopy, culture and site-specific NAAT according to the resulting hypotheses rather than ordering an undifferentiated panel.
03ResultsTreat the cause and close the loopA syndrome or laboratory diagnosis is available, or symptoms continue despite negative results.+
1Use organism-specific regimens and document allergy, pregnancy, interactions, adherence and partner-management advice.
2Arrange a result-delivery plan, accurate abstinence interval and disease-specific test-of-cure or reinfection testing where indicated.
3Re-examine persistent symptoms for dermatosis, atrophy, foreign body, fistula, malignancy or chronic pain instead of repeatedly prescribing antimicrobials.