Urine Examination

Overview

Urinalysis reflects kidney/urinary tract function + metabolic/systemic status. Should precede other invasive renal investigations. 3 parts: physical, chemical, microscopic.

Specimen collection/preservation

Midstream (routine), clean-catch (culture), catheter (bedridden/obstruction), infant (plastic bag/suprapubic aspiration). Examine within 2hr; else refrigerate or preserve (toluene, conc. HCl, thymol/formaldehyde).

Physical exam

Volume: normal 600-2000mL/24h. Polyuria (>2L) — physiological/diabetes/renal disease/diuretics/DI. Oliguria (<500mL) — fluid restriction, loss, renal disease, transfusion reaction, Addison’s. Anuria (<125mL) — renal ischaemia, tumours, stones.

Colour: normal straw-amber (urochrome). Colourless=dilute; dark brown=oliguria; smoky=haematuria; cola=intravascular haemolysis; yellow-brown=bilirubin; orange-brown=urobilinogen; dark on standing=alkaptonuria; milky=pus/chyle.

Chyluria (lymph in urine — filariasis, lymphatic obstruction). Lipiduria (fat globules — nephrotic syndrome, fractures).

Specific gravity: normal 1.003-1.035 (avg 1.016). ↑ by glycosuria/proteinuria/dehydration; ↓ by ↑fluid intake/DI/end-stage kidney. Isosthenuria (fixed at 1.010) = severe renal damage (CKD), lost concentrating+diluting ability.

Chemical exam

Proteinuria = glomerular injury marker. Tests: heat+acetic acid, sulfosalicylic acid (all protein types), Heller’s (nitric acid ring), dipstick (mainly albumin — misses Bence Jones). Esbach’s albuminometer = quantitative 24hr (nephrotic syndrome workup).

Categories: heavy(>4g/day)/moderate(1-4g)/mild(<1g); or renal/prerenal/postrenal.

• Selective (small proteins only, <100kDa)
• Nonselective (wider range incl. large proteins)
• Bence Jones proteins = Ig light chains, multiple myeloma marker; unique thermal solubility (ppt 40-60°C, redissolve ~100°C, reappear on cooling)
• Microalbuminuria (20-200mg/L, below conventional detection) = early reversible glomerular damage; predicts renal+CV mortality in diabetes, CV morbidity in hypertension

Glycosuria: normal blood glucose 70-120mg/dL, renal threshold ~180-200mg/dL. Benedict’s test (semiquantitative, NOT glucose-specific, any reducing sugar) vs dipstick (glucose-specific, oxidase/peroxidase). Renal glycosuria = benign, ↓threshold, unrelated to diabetes. Alimentary glycosuria = transient postprandial spillover. Other sugars: fructosuria (Seliwanoff’s), lactosuria (Rubner’s), pentosuria (Bial’s).

Ketonuria: 3 ketone bodies — acetoacetic acid, β-hydroxybutyric acid, acetone. Reflects METABOLIC not renal status (fat used as fuel — DKA or starvation). Tests: Rothera’s (acetoacetic acid+acetone, purple ring), Gerhardt’s/ferric chloride (acetoacetic acid, less sensitive), Hart’s (β-hydroxybutyric acid — what other 2 miss), dipstick.

Causes: DKA; non-diabetic — starvation, vomiting/diarrhoea, von Gierke’s disease, hyperemesis gravidarum, lactic acidosis.

Bilirubin/urobilinogen: bilirubin normally ABSENT (only conjugated can be excreted). Fouchet’s test, dipstick (diazo→azobilirubin).

• Obstructive jaundice: bilirubin present, urobilinogen absent
• Hepatocellular: bilirubin appears BEFORE clinical jaundice (early marker)
• Haemolytic: bilirubin ABSENT (unconjugated, not water-soluble), urobilinogen ↑

Urobilinogen tests: Ehrlich’s test, dipstick.

Blood: haematuria (intact RBCs) vs haemoglobinuria (free Hb, intravascular haemolysis) vs myoglobinuria (crush injury). Tests (benzidine, orthotoluidine, dipstick) share principle: haem peroxidase-like activity liberates O2 from H2O2 → colour change. Dysmorphic RBCs = glomerular bleeding.

Microscopic exam

Sediment = organized (cells, casts, crystals) + unorganized (crystalline/amorphous, pH-dependent).

Cells: RBCs (>2/hpf abnormal; dysmorphic = glomerular). WBCs (>5/hpf = pyuria = UTI; + leukocyte casts = renal origin). Glitter cells (swollen neutrophils, Brownian motion granules — dilute urine, chronic pyelonephritis). Epithelial cells (transitional/squamous; malignant cells in bladder tumours).

Casts: formed ONLY in kidney (Tamm-Horsfall protein, distal/collecting tubules) — always = renal disease. Cylindrical, parallel sides, rounded ends (cylindroids = abortive, tapering). Classified by matrix (hyaline/waxy), cells (RBC/leukocyte/epithelial/mixed), inclusions (granular/fatty), pigments.

Crystals: not normally present. Oxalate/urate/cystine = renal stone history; urate alone = gout. Acidic urine: oxalates/urates/cystine. Alkaline urine: phosphates/carbonate/ammonium urate.

Clinical relevance

Recurring pattern across glycosuria/ketonuria/bilirubin/blood tests = colour-change reaction from a specific chemistry (reducing sugar reduction, haem peroxidase activity, diazo coupling) — shared design logic, not independent facts. Bilirubin present/absent pattern across 3 jaundice types = one of highest-yield reasoning chains — distinguishes obstructive/hepatocellular/haemolytic jaundice from ONE simple test. Bence Jones thermal solubility = distinctive bedside screening clue for myeloma. Casts formed exclusively in kidney = why their presence localises abnormality to renal parenchyma, unlike crystals/free cells which can arise anywhere along the tract.

Overview

Urine analysis (urinalysis) reflects the functional state of the kidneys and urinary tract, and also provides information about metabolic or systemic (non-renal) disorders. It should precede all other invasive/non-invasive investigations for renal function, given how much information a simple, non-invasive test yields. Examination comprises three components: physical, chemical, and microscopic.

Specimen Collection and Preservation

• Midstream specimen — used for routine urine examination; the first part of voided urine is discarded, and a midstream portion collected.
• Clean-catch specimen — for culture and sensitivity; external genitalia cleaned before collection.
• Catheter specimen — for culture/sensitivity in bed-ridden patients or those with urinary tract obstruction.
• Infant collection — via a clean plastic bag attached around the genitalia; suprapubic bladder aspiration is used for bacteriological examination.

Urine should be examined within 2 hours of collection. If delay is unavoidable, preserve by refrigeration (without preservative), or with preservatives such as toluene (thin surface layer), concentrated HCl, or thymol/formaldehyde (the latter preserves cells and casts).

Physical Examination

Volume — a healthy adult excretes 600–2000 mL/24h (infants: 300–600 mL/day).

• Polyuria (>2 L/24h) — physiological (increased fluid intake) or pathological (diabetes mellitus, chronic renal disease, diuretics, diabetes insipidus, primary aldosteronism).
• Oliguria (<500 mL/24h) — restricted fluid intake, excessive fluid loss (haemorrhage, burns, dehydration, shock), renal disease (acute glomerulonephritis, nephrotic syndrome, acute tubular necrosis), incompatible transfusion, heavy metal poisoning, Addison’s disease.
• Anuria (<125 mL/24h) — renal ischaemia, tumours, renal stones.

Colour — normal urine is straw to amber (urochrome pigment, excretion proportional to metabolic rate).

Chyluria — a rare condition where urine contains lymph, from obstruction/rupture of lymphatics into the renal pelvis, ureters, bladder, or urethra; causes include filariasis, abdominal lymphadenopathy, tumours.

Lipiduria — fat globules (triglycerides, cholesterol) in urine, seen in nephrotic syndrome and bone fractures.

Specific gravity — reflects the kidney’s concentrating power; normal range 1.003–1.035 (average 1.016). Measured by urinometer, refractometer, or dipstick (urinometer/refractometer are more accurate). Increased by glycosuria, proteinuria, dehydration; decreased by excessive fluid intake, diabetes insipidus, end-stage kidney disease. Isosthenuria — a fixed specific gravity of 1.010 — indicates severe renal damage (chronic renal failure) with loss of both concentrating and diluting ability.

Chemical Examination

Proteinuria

Detectable urinary protein, indicating glomerular injury. Tests: heat-and-acetic-acid test, sulfosalicylic acid test (detects all protein types — albumin, globulin, glycoproteins, Bence Jones proteins), Heller’s test (nitric acid ring test), and the dipstick method (based on the “protein error of pH indicators” — detects mainly albumin, so may miss Bence Jones protein). Esbach’s albuminometer gives quantitative 24-hour protein estimation, needed for suspected nephrotic syndrome (>3.5 g/24h) or orthostatic proteinuria.

Categories: heavy (>4 g/day), moderate (1–4 g/day), mild (<1 g/day); or structurally as renal (glomerular/tubular), prerenal, and postrenal.

• Selective proteinuria — only intermediate-sized proteins (<100 kDa, e.g. albumin, transferrin) leak through.
• Nonselective proteinuria — a wider range including larger proteins (e.g. immunoglobulins) leak through.
• Bence Jones proteins — immunoglobulin light chains, characteristic of multiple myeloma (also macroglobulinaemia, lymphoma); precipitate at 40–60°C, redissolve near 100°C, reappear on cooling — a distinctive thermal solubility pattern useful diagnostically.
• Microalbuminuria — persistent urinary albumin excretion of 20–200 mg/L, below the detection threshold of conventional protein tests; indicates early, potentially reversible glomerular damage. Clinically important in diabetes mellitus (predicts renal and cardiovascular mortality) and essential hypertension (predicts cardiovascular morbidity/mortality).

Glycosuria (Reducing Substances)

Normal blood glucose is 70–120 mg/dL (rising to 120–160 mg/dL postprandially); glucose is normally fully filtered and reabsorbed at the proximal tubule. Exceeding the renal threshold (usually >180–200 mg/dL) causes glycosuria, as in diabetes mellitus.

• Benedict’s qualitative test — semiquantitative; based on reduction of cupric sulphate to cuprous oxide by reducing substances, in hot alkaline medium; colour change (blue → green → yellow → orange/red) tracks sugar amount. Not specific for glucose — detects any reducing sugar.
• Dipstick method — uses glucose oxidase/peroxidase/chromogen; specific for glucose.
• Renal glycosuria — a benign condition from reduced renal threshold, unrelated to diabetes, without classical diabetic symptoms — should not be mistaken for diabetes mellitus.
• Alimentary (lag storage) glycosuria — transient postprandial glucose spillover, seen in some normal individuals and in hepatic disease, hyperthyroidism, peptic ulcer.
• Other sugars: fructosuria (Seliwanoff’s test), lactosuria (Rubner’s test), pentosuria (Bial’s test).

Ketonuria

Ketone bodies — acetoacetic acid, β-hydroxybutyric acid, acetone — reflect metabolic, not renal, status; they accumulate when fat is used as an energy source due to a carbohydrate metabolism defect (diabetic ketoacidosis) or during starvation. Tests: Rothera’s test (purple ring with sodium nitroprusside, detects acetoacetic acid/acetone), Gerhardt’s (ferric chloride) test (detects acetoacetic acid specifically, less sensitive), Hart’s test (detects β-hydroxybutyric acid, which the other two miss), and dipstick (detects acetoacetic acid).

Causes: diabetic ketoacidosis; non-diabetic — starvation, prolonged vomiting/diarrhoea, glycogen storage disease (von Gierke’s), hyperemesis of pregnancy, lactic acidosis (shock, renal/liver failure, drugs).

Bilirubin and Urobilinogen

Bilirubin is normally absent from urine (only conjugated bilirubin, if present, appears — unconjugated bilirubin is not water-soluble and cannot be excreted renally). Tests: Fouchet’s test (ferric chloride oxidises bilirubin to green biliverdin), dipstick (diazo reaction, forms azobilirubin).

• Obstructive jaundice — bilirubin present, urobilinogen absent.
• Hepatocellular jaundice — bilirubin may appear before jaundice is clinically apparent (useful early marker).
• Haemolytic jaundice — bilirubin absent (the excess is unconjugated, not water-soluble); but urobilinogen is increased.

Urobilinogen tests: Ehrlich’s test (pink-to-cherry-red aldehyde complex), dipstick.

Blood in Urine

Distinguishes haematuria (intact RBCs — renal stones, RCC, glomerular disease), haemoglobinuria (free haemoglobin — intravascular haemolysis), and myoglobinuria (crush injury, strenuous exercise). Tests (benzidine, orthotoluidine, dipstick) share a common principle: the peroxidase-like activity of haem liberates oxygen from hydrogen peroxide, producing a colour change. Glomerular bleeding classically produces dysmorphic (distorted-shape) red cells, distinguishing it from lower urinary tract bleeding.

Microscopic Examination

Urinary sediment/deposit is divided into organized (cells, casts, crystals, other formed elements) and unorganized (crystalline/amorphous material, varying with urine pH) deposits.

Cells

• RBCs (>2/hpf abnormal) — bleeding anywhere from glomerulus to urethra; dysmorphic RBCs point specifically to glomerular disease.
• WBCs (>5/hpf, mainly neutrophils = pyuria) — indicates urinary tract infection; accompanied by leukocyte casts, points to renal origin. Glitter cells — swollen neutrophils with Brownian-motion cytoplasmic granules, seen in dilute/hypotonic urine, chronic pyelonephritis, lower UTI.
• Epithelial cells — transitional (urinary tract) or squamous (genital tract contamination); malignant cells may be seen in bladder tumours.

Casts

Formed only in the kidney — always indicative of renal disease. Formed by solidification of Tamm-Horsfall protein, secreted by the distal convoluted and collecting tubules, forming a fibrillar meshwork that traps cells, cell fragments, or granular material. Cylindrical with parallel sides and rounded ends (cylindroids are abortive casts — one tapering end, non-parallel sides). Classified by matrix (hyaline, waxy), trapped cells (RBC, leukocyte, epithelial, mixed casts), inclusions (granular, fatty), or pigments (haemoglobin, myoglobin, bilirubin).

Crystals

Not normally present. Oxalate, urate, and cystine crystals occur with a history of renal stones; urate crystals alone occur in gout. Oxalates/urates/cystine favour acidic urine; phosphates, calcium carbonate, and ammonium urates favour alkaline urine.

Clinical Relevance

• The recurring pattern across glycosuria, ketonuria, bilirubin, and blood tests — a colour-change reaction driven by a specific chemical principle (reducing sugar reduction, peroxidase-like haem activity, diazo coupling) — is worth recognising as a shared design logic rather than memorising each test’s chemistry independently; nearly every urine dipstick component works by the same basic strategy of converting a biochemical presence into a visible colour change.
• Bilirubin’s presence/absence pattern across the three jaundice types (present-without-urobilinogen in obstructive; early-appearing in hepatocellular; absent-with-raised-urobilinogen in haemolytic) is one of the highest-yield diagnostic reasoning chains in this topic, since it directly distinguishes the three major categories of jaundice from a single, simple urine test.
• Bence Jones proteins’ unusual thermal solubility (precipitate at 40–60°C, redissolve near 100°C, reappear on cooling) is a distinctive enough pattern that it functions as a bedside screening clue for multiple myeloma, worth remembering as a specific fact rather than folding into generic “abnormal protein” recall.
• Casts being formed exclusively in the kidney (from Tamm-Horsfall protein in the distal tubule) is what makes their presence diagnostically decisive for localising a urinary abnormality to renal parenchyma, in contrast to crystals or free cells, which can arise anywhere along the urinary tract and are therefore less specific for localisation.

No Rendered Diagram for This Topic

Urine examination is a laboratory reference topic (physical/chemical/microscopic test panels, each test’s principle and interpretation) rather than a disease mechanism — a rendered diagram would only redraw the reference tables already in notes.md.

Hand-Draw Suggestion

Draw the bilirubin/urobilinogen pattern across the three jaundice types by hand as a quick 3x2 grid (Obstructive / Hepatocellular / Haemolytic × Bilirubin / Urobilinogen present-absent-increased) — this is the single highest-yield reasoning chain in the topic and is best learned by active recall of the grid rather than a process diagram.

Multiple Choice Questions (3)