Biochemistry · Topic
Urinalysis !
Urinalysis combines appearance, dipstick and microscopy; it points to infection, kidney disease, diabetes and liver problems.
Updated 2026-11-01
Key facts
- Three parts: physical (colour, clarity, specific gravity), chemical by dipstick (pH, protein, glucose, ketones, blood, bilirubin, urobilinogen, nitrite, leukocyte esterase) and microscopic (cells, casts, crystals).
- Nitrite + leukocyte esterase suggest urinary infection; nitrite needs nitrate-reducing bacteria (Enterobacterales) and urine held for some hours.
- Glycosuria appears when blood glucose exceeds the renal reabsorption threshold (SGLT2) or when the tubule fails (Fanconi, SGLT2 inhibitors).
- Dipstick positive for blood without red cells under the microscope: myoglobin (rhabdomyolysis) or free haemoglobin (haemolysis).
- Casts: red cell = glomerulonephritis; white cell = pyelonephritis or interstitial nephritis; 'muddy brown' granular = acute tubular necrosis; waxy = chronic disease.
In detail
- Sample: clean-catch midstream urine, ideally the first morning void and analysed promptly, because cells and casts break down and bacteria multiply.
- Specific gravity: reflects concentrating ability; fixed low (isosthenuria) in advanced kidney disease or diabetes insipidus; high in dehydration or after contrast.
- Protein: the dipstick mainly detects albumin; it misses light chains (myeloma), which need other tests. The protein/creatinine or albumin/creatinine ratio quantifies.
- Ketones: the dipstick detects acetoacetate (and acetone), not β-hydroxybutyrate, so it can underestimate ketoacidosis.
- Urine bilirubin: only the conjugated (direct) form passes, so it appears in cholestasis and hepatitis, not in haemolysis; urobilinogen rises in haemolysis and liver disease and is absent in complete obstruction.
- Crystals: calcium oxalate (stones, ethylene glycol), uric acid (acid urine, gout, tumour lysis), struvite (Proteus infection, alkaline urine), hexagonal cystine (cystinuria).
- pH: alkaline with urea-splitting bacteria; acid in metabolic acidosis of non-renal cause and high-protein diets.
- Also called
- Urine test, Dipstick, Urine sediment, Urine microscopy
Clinical notes
- Asymptomatic bacteriuria is not treated except in pregnancy and before urological procedures.
- A sediment with dysmorphic red cells and red cell casts points to glomerular disease and calls for assessment of kidney function.
- High-dose vitamin C can give false negatives for glucose, blood and nitrite on the dipstick.
Related conditions
- Urinary tract infection (acute cystitis)
- Kidney stones (urolithiasis)
- Diabetic ketoacidosis
- Chronic kidney disease
- Acute pyelonephritis
- Cystinuria
Related
- Glucose
- Acetoacetate (acetoacetic acid)
- Bilirubin
- Creatinine and estimated glomerular filtration rate (eGFR)
- Serum albumin as a lab test
Test yourself
Think of the answer, then tap the question to see it.
What does a dipstick positive for blood without red cells under the microscope suggest?
Myoglobinuria (rhabdomyolysis) or haemoglobinuria (haemolysis), because the dipstick detects the peroxidase activity of haem.
Why can the ketone dipstick underestimate ketoacidosis?
It detects acetoacetate and acetone but not β-hydroxybutyrate, the ketone that predominates in severe ketoacidosis.
Which bilirubin appears in urine, and why?
Only the conjugated (direct) form, because it is water-soluble; unconjugated bilirubin travels on albumin and is not filtered.
What do red cell casts indicate?
Bleeding of glomerular origin, as in glomerulonephritis.
Why does a negative nitrite not rule out urinary infection?
Some bacteria (enterococci, staphylococci) do not reduce nitrate, and urine must stay hours in the bladder for nitrite to form.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Urinalysis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Urinalysis: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Protein in Urine: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Glucose in Urine Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Nitrites in Urine: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Leukocyte esterase urine test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Urine specific gravity test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.