Urinalysis
OVERVIEW
- Visual inspection
- Dipstick
- Microscopy – cells, casts and crystals
- Electrolytes – Na, K, Ca
- Osmolality
- Urinary Cystatin C
VISUAL INSPECTION
- yellow: normal
- pale/clear: diuretics, diabetes insipidus
- milky: lipiduria, UTI
- pink/opalescent: haemoglobinuria
- pink/cloudy -> red: haematuria
- tea coloured: myoglobinuria, metronidazole, porphyria
- blue: methylene blue administration
- green: high dose propofol
- orange: rifampicin, conjugated bilirubin
- grey/black: homogentisic acid in alkaptonuria, melanogens in disseminated melanoma, Addisons disease
DIPSTICK
- specific gravity: normal 1.003-1.030, increased: hyperglycaemia, proteinuria, SIADH, intravascular dehydration, radiocontrast, deceased: DI, GN, pyelonephritis, renal failure
- pH: normal 4.5-8, < 6: acidosis and pre-renal failure, >7: alkalosis and alkalinising agents, RTA
- glucose: hyperglycaemia or renal glycosuria
- blood: positive in haematuria, haemoglobinuria, myoglobinuria
- protein: albuminuria (requires further investigation – GN, MM, malignancy, pyelo)
- BHCG: pregnancy status
- WCC: pyuria
- nitrites: bacterial infection (most convert nitrates to nitrite)
- ketones: starvation, diabetic or alcoholic ketoacidosis, carbohydrate free and high fat+protein diet
- bilirubin and urobilinogen: conjugated -> excess production or biliary obstruction, urobilinogen -> absent in biliary obstruction
MICROSCOPY
Cells
- RBC: renal disease (low specificity), dysmorphic cells -> GN
- WCC: infection (low specificity), renal calculi, interstitial nephritis, GN, vasculitis, infarction
- tubular cells: tubular disease
- eosinophils: interstitial nephritis
Casts
- hyaline: can be normal
- red cell casts: glomerular disease (GN), endocarditis
- white cell casts: pyelonephritis, interstitial nephritis, vasculitis, infarction
- granular: non-specific to many renal parenchymal disease
- fatty: diabetic nephropathy and nephrotic syndrome
- epithelial: recovery phase of ATN
- eosinophilia: interstitial nephritis and atheroembolism
Crystals
- oxalate crystals: ethylene glycol poisoning
- calculi: calcium, magnesium-ammonium-phosphate, urate, cysteine
- drugs: sulphonamides, methotrexate, acyclovir, radiocontrast
ELECTROLYTES
Sodium
- increased loss: hypoadrenalism, salt-losing nephropathy, ATN, excess salt loads, SIADH
- decreased loss: hyperaldosteronism, Cushing syndrome, intravascular dehydration, pre-renal failure, hepatorenal syndrome
Potassium
- helps clarify whether loss is renal or extra-renal
- increased loss: hypomagnesaemia, ATN, loop and thiazide diuretics, hyperaldosteronism, Cushing syndrome, amphotericin B
Chloride
- may help clarify the mechanism of metabolic alkalosis
- UrCl- <10mmol/L: intravascular volume depletion (diuretics, vomiting)
- UrCl- >10mmol/L: intravascular volume expansion + hypokalaemia (hyperaldosteronism)
Calcium
- may clarify deranged calcium homeostasis
- increased loss: loop diuretics, idiopathic hypercalcuria, hypoparathyroidism, vitamin D intoxication, renal failure, RTA, sarcoidosis
- decreased excretion: hyperparathyroidism, malabsorption syndromes, vitamin D deficiency, thiazide diuretics
OSMOLARITY
- like Na+ is a marker of hydration and concentration ability but also reflects excreted osmotically active substances (ie. mannitol, radiocontrast, glucose)
URINARY CYSTATIN C
- predictor of severity of acute tubular dysfunction in a range of renal pathologies.
References and Links
- Unusual urine – Clinical Cases
- CCC – Urinalysis
- CCC – Urine electrolytes – Urinary anion gap
- Urinalysis Overview Table
- Laboratory Urinalysis
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Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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