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Purpose and principlesIndications, selection and cautionsMethod and interpretationClinical next stepsProcedure and medicine safetyRisks, monitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Urinalysis and urine microscopy

Renal · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Haematuria with rapidly falling renal function, proteinuria, hypertension, red-cell casts or pulmonary haemorrhage suggests rapidly progressive glomerulonephritis and needs urgent nephrology contact. Pyuria with sepsis and obstruction requires urgent drainage assessment; a urine result must not delay resuscitation.

Purpose and principles

Use dipstick, quantitative protein testing, culture and urine sediment together to localise renal and urinary disease while recognising contamination, false results and time-critical nephritic patterns.

Urinalysis is a low-cost physiological biopsy, but only when collection and interpretation are disciplined. Reagent pads screen chemical properties; microscopy identifies cells, casts, organisms and crystals; culture establishes bacterial growth; ACR or PCR quantifies protein. None substitutes for the others.

Casts form in renal tubules and therefore help localise disease above the lower urinary tract. Red-cell casts are strongly concerning for glomerulonephritis, while renal tubular epithelial cells and coarse granular casts can support acute tubular injury. Absence of an active sediment does not exclude biopsy-proven disease, particularly after delay or dilute urine.

The clinical question determines action. Asymptomatic bacteriuria, sterile pyuria, non-visible haematuria and nephritic urine have different pathways. Treat the patient and source, not every colour change or isolated dipstick pad.

Key points

  • A fresh midstream clean-catch sample with documented timing and symptoms is the starting point. Catheter, menstruation, vigorous exercise, antiseptic contamination and delayed analysis can change results.
  • Dipstick 'blood' detects haem pigment, not intact red cells. Haematuria, haemoglobinuria and myoglobinuria can all be positive; microscopy and the clinical setting separate them.
  • Nitrite supports nitrate-reducing bacteria but is insensitive with frequent voiding, low dietary nitrate or organisms that do not reduce nitrate. A negative result never excludes UTI or pyelonephritis.
  • Leucocyte esterase reflects white cells and can occur with infection, stones, interstitial nephritis, tuberculosis or contamination. Culture and symptoms determine whether antibiotics are appropriate.
  • Dipstick protein mainly detects albumin and is affected by concentration and pH. NICE recommends quantitative urine ACR for initial detection of clinically important proteinuria.
  • Glucose on dipstick can reflect hyperglycaemia or reduced proximal tubular reabsorption, including SGLT2 inhibitor effect. Check blood glucose and medicines before diagnosing diabetes.
  • Ketones indicate fat metabolism and can accompany diabetic ketoacidosis, starvation, vomiting or pregnancy. In SGLT2-treated patients, clinically important ketoacidosis can occur with less marked hyperglycaemia.

Indications, selection and cautions

Glomerular sedimentRed flag

Protein with dysmorphic erythrocytes or red-cell casts, hypertension, oedema and impaired function favours glomerular inflammation. Systemic rash, haemoptysis or rapidly rising creatinine increases urgency.

Tubular injury sedimentRed flag

Renal tubular epithelial cells and pigmented granular casts in an ischaemic, septic or toxic context support acute tubular injury. Creatinine trajectory and urine output remain necessary for severity.

Infective patternRed flag

Dysuria, frequency or fever with pyuria, bacteriuria and sometimes nitrite supports infection. Flank pain, rigors, pregnancy, male sex, immunosuppression or obstruction changes complexity and escalation.

Sterile pyuria

White cells without routine bacterial growth can reflect prior antibiotics, stones, interstitial nephritis, sexually transmitted infection, renal tuberculosis or contamination. Repeat and target tests rather than extending empirical antibiotics blindly.

Pigment without red cellsRed flag

Strong dipstick blood with few or no erythrocytes suggests myoglobin or free haemoglobin. Muscle pain, high CK or haemolysis tests identify a systemic pigment source that can itself cause AKI.

Contaminated specimen

Many squamous epithelial cells, mixed flora and discordant symptoms suggest poor collection. Repeat a correctly obtained sample unless the patient is too unwell for diagnostic delay.

Method and interpretation

  1. 01
    Fresh reagent-strip urinalysisFirst step
    Why
    Screen blood, leucocytes, nitrite, protein, glucose, ketones, pH and concentration at the bedside or laboratory.
    Interpretation and limitations
    Record exact grade rather than 'positive'. Check expiry, timing and discolouring medicines; correlate every pad with symptoms, ACR, microscopy or blood testing as appropriate.
  2. 02
    Urine albumin-to-creatinine ratio
    Why
    Quantify albuminuria sensitively and classify chronic kidney risk.
    Interpretation and limitations
    Use an early-morning confirmation for ACR 3 to 70 mg/mmol in stable adults under NICE/UKKA guidance; values above 70 generally do not require confirmation before action, but acute illness can transiently raise albumin.
  3. 03
    Urine microscopy
    Why
    Identify erythrocyte morphology, leucocytes, epithelial cells, casts, organisms and crystals.
    Interpretation and limitations
    Request and examine promptly when glomerulonephritis, tubular injury or crystals are suspected. Technique and delay affect yield; a negative sediment is not an absolute exclusion test.
  4. 04
    Midstream urine culture and sensitivities
    Why
    Confirm clinically relevant bacteriuria and direct antimicrobial choice.
    Interpretation and limitations
    Collect before antibiotics where safe and report pregnancy, catheter and symptoms. Mixed growth often indicates contamination, while lower counts may still matter in a strongly symptomatic patient.

Clinical next steps

01Active nephritic urineEscalate possible glomerulonephritisFirst stepEscalationBlood and protein with impaired function, hypertension, casts or systemic inflammatory features.+
  1. 1Repeat a clean sample, quantify ACR/PCR, obtain urgent renal biochemistry, FBC and blood pressure, and review baseline and urine output.
  2. 2Discuss promptly with nephrology; send targeted complements, ANCA, ANA, anti-GBM, infection and paraprotein testing as advised rather than delaying referral for a complete panel.
  3. 3If pulmonary haemorrhage, oliguria, severe hypertension, hyperkalaemia or rapid deterioration is present, admit for emergency renal assessment and possible biopsy/treatment.
02Possible UTICulture and classify complexityUrinary symptoms, fever or systemic illness with leucocytes, nitrite or bacteriuria.+
  1. 1Assess sepsis, pregnancy, flank pain, retention, stones, catheter, male anatomy and immunosuppression; obtain culture before treatment when this does not delay sepsis antibiotics.

Procedure and medicine safety

Treats clinically diagnosed bacterial cystitis, pyelonephritis or urosepsis while culture refines therapy.

Empirical antimicrobial for urinary infection

Select agent, dose and duration from current local and NICE guidance using site, severity, culture history, allergy, pregnancy and renal function.

Do not treat an isolated dipstick or most asymptomatic bacteriuria. Obstruction needs drainage, and several antibiotics require renal adjustment or can worsen potassium and kidney function.

Explains expected glycosuria and highlights the possibility of euglycaemic ketoacidosis when ketones and systemic symptoms occur.

SGLT2 inhibitor awareness

Continue or pause only according to an individualised clinical sick-day and peri-procedure plan; timing varies by medicine, illness severity and procedure.

Glycosuria is pharmacological and does not prove uncontrolled diabetes. Nausea, abdominal pain, tachypnoea or ketones during illness requires urgent blood ketone and acid-base assessment.

Risks, monitoring and follow-up

  • Repeat urinalysis after transient triggers settle and confirm persistent albuminuria quantitatively rather than following dipstick intensity as a surrogate.
  • For nephritic findings, trend creatinine, potassium, bicarbonate, urine output, blood pressure and ACR/PCR while nephrology determines biopsy and immunosuppression urgency.
  • For treated infection, review culture and narrow or change antibiotics, documenting renal-dose adjustments and clinical response rather than ordering routine test-of-cure for everyone.
  • Persistent non-visible haematuria needs blood pressure, eGFR and ACR surveillance even after negative urological investigation because renal disease can evolve.
  • When pigment nephropathy is possible, follow CK or haemolysis markers, potassium, calcium, phosphate, fluid balance and renal function through the acute pathway.

Special situations

Blood pad detects chemistry

The reagent reacts to haem peroxidase activity. Microscopy distinguishes intact urinary red cells from myoglobin or haemoglobin and prevents three different diseases sharing one label.

Casts carry an address

Because casts form in tubules, cells embedded within them localise inflammation or bleeding to the kidney rather than bladder or urethra.

Albumin needs quantification

A concentrated urine can look strongly protein-positive and dilute urine weakly positive. ACR corrects partly for concentration and detects lower albumin amounts more sensitively.

Nitrite is a rule-in clue

Adequate bladder dwell time and a nitrate-reducing organism are required. Frequent voiding or enterococci can produce symptomatic infection with negative nitrite.

A bland sediment can still be serious

Obstruction, vascular disease and some interstitial or early glomerular processes may produce few cells. Always integrate urine findings with creatinine, output and imaging.

Common pitfalls

  1. 01

    Calling dipstick blood haematuria without confirming whether urinary erythrocytes are present.

  2. 02

    Excluding infection because nitrite is negative in a symptomatic or septic patient.

  3. 03

    Treating leucocyte esterase alone with repeated antibiotics despite sterile cultures.

  4. 04

    Using dipstick protein instead of ACR to detect and classify lower-level albuminuria.

  5. 05

    Waiting for every immunology result before discussing rapidly progressive nephritic findings with nephrology.

  6. 06

    Assuming crystals prove a stone or that absent crystals exclude stone disease.

Practice

Two practice questions

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Question 1 of 2
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RenalOriginal SBA

Blood without erythrocytes

Urine dipstick is strongly positive for blood after prolonged limb compression, but microscopy shows almost no red cells. The patient has muscle pain. What is the best explanation?

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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG203 chronic kidney disease recommendationsAlbuminuria and haematuria testing and referral guidance.
  • UKKA kidney-function measurement guideACR as first-line quantitative protein assessment.
  • NICE NG148 acute kidney injury recommendationsUrinalysis and cause investigation in acute dysfunction.
  • BAUS non-visible haematuria guideUrological interpretation and escalation of urinary blood.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
  • Dysmorphic red cells and red-cell casts support glomerular bleeding; white-cell casts suggest renal parenchymal inflammation; granular 'muddy brown' casts support tubular injury but sediment sensitivity is imperfect.
  • Crystals depend on urine pH, concentration, medicines and storage. Their presence does not prove a stone, while stone disease can occur without diagnostic crystalluria.
  • Interpret the whole pattern: blood plus albumin and impaired function differs from isolated nitrite, and a bland dipstick does not exclude obstruction or early interstitial disease.
  • 05
    Serum creatinine, potassium, bicarbonate and FBC
    Why
    Determine renal impact and systemic severity of the urine abnormality.
    Interpretation and limitations
    A rising creatinine, hyperkalaemia or acidosis with active sediment lowers the threshold for urgent renal referral. Leucocytosis or anaemia can guide infection, haemolysis and chronicity assessment.
  • 06
    Creatine kinase and haemolysis screen
    Why
    Investigate dipstick haem with absent urinary erythrocytes.
    Interpretation and limitations
    Marked CK supports rhabdomyolysis; anaemia, bilirubin, LDH, haptoglobin and blood film support intravascular haemolysis. Both require cause-directed systemic management.
  • 2Choose antimicrobial and duration from the current local/NICE pathway, prior cultures, allergy, renal function and resistance risk rather than dipstick alone.
  • 3Arrange imaging or urology review for suspected infected obstruction, recurrence, atypical organism or failure to improve; do not keep repeating empirical courses without source review.
    • 03Unexpected dipstickVerify before labelling diseaseAsymptomatic blood, protein, glucose, leucocytes or pigment found incidentally.+
    1. 1Exclude transient collection factors such as menstruation, exercise, fever and contamination, then repeat under correct conditions at the guideline interval.
    2. 2Quantify albumin with ACR, culture when infection is plausible, examine microscopy for persistent blood and check glucose or CK for the relevant chemical signal.
    3. 3Route persistent haematuria through age-appropriate urology criteria and renal haematuria through ACR, eGFR and nephrology criteria; these routes may need to run together.