Interpret · Fluids & specimens

Urinalysis Lab

The cheapest kidney biopsy in the building. Dipstick, sediment, and the urine chemistry that classifies AKI, sodium disorders, and acid-base problems.

The sediment, seen

Casts and crystals under the microscope. The muddy brown granular cast is the one that separates tubular injury from a dry patient; the envelope crystal is calcium oxalate, the commonest stone former.

Urine microscopy showing several muddy brown granular casts — Muddy brown granular casts: the sediment of acute tubular necrosis. This field, in an oliguric patient with a rising creatinine, moves the diagnosis from prerenal to intrinsic.Ajay Kumar Chaurasiya, via Wikimedia Commons · CC BY 4.0 · source

Urine microscopy showing a single coarse granular cast — A coarse granular cast: a tubular mould packed with degenerated cell debris. One is a hint; many, pigmented, are acute tubular injury.Ajay Kumar Chaurasiya, via Wikimedia Commons · CC BY-SA 4.0 · source

Urine microscopy showing envelope-shaped calcium oxalate dihydrate crystals — Calcium oxalate dihydrate: the envelope, a square with its diagonals drawn. Common in concentrated urine and in stone formers; in numbers after an ethylene glycol ingestion.Ajay Kumar Chaurasiya, via Wikimedia Commons · CC BY-SA 4.0 · source

Urine microscopy showing clumps of amorphous urate crystals — Amorphous urates: granular pinkish clumps in acid, concentrated or cooled urine. Usually a red herring, unless the story is tumour lysis.Ajay Kumar Chaurasiya, via Wikimedia Commons · CC BY-SA 4.0 · source

Dysuria and a positive dipstick

A 26-year-old with two days of dysuria and frequency, no fever or flank pain.

Dipstick

Leukocyte esterase	Positive
Nitrites	Positive
Blood	Trace
Protein	Negative
Glucose	Negative

Microscopy

Many white cells
Bacteria present
No casts

What does the nitrite result add beyond the leukocyte esterase?

AKI: what is the kidney trying to do?

The 74-year-old with pneumonia and a climbing creatinine from the lab module. You send urine studies before any fluid decision.

Dipstick

Protein	Trace
Blood	Negative

Microscopy

Bland sediment
Occasional hyaline casts
No granular casts

Urine chemistry

Urine sodium	12 mmol/L
Urine creatinine	9200 µmol/L
FENa	0.4 %
Urine osmolality	620 mOsm/kg

What is this kidney doing?

The urine that explains a sodium of 118

The euvolemic hyponatremic patient from the lab module. Her urine studies return.

Dipstick

Specific gravity	1.020

Urine chemistry

Urine osmolality	520 mOsm/kg
Urine sodium	64 mmol/L
Serum osmolality	246 mOsm/kg

Serum osmolality 246, urine osmolality 520. What does that pairing mean?

Normal gap acidosis: gut or kidney?

The traveler with diarrhea from the blood gas module. To prove the mechanism, you send spot urine electrolytes.

Dipstick

pH	5.2

Urine chemistry

Urine sodium	42 mmol/L
Urine potassium	28 mmol/L
Urine chloride	95 mmol/L
Urine anion gap	−25 mmol/L

The urine anion gap is negative. What does that say?

Tea-colored urine and puffy eyes

A 22-year-old presents with dark urine, facial swelling, and a BP of 168/98 two weeks after pharyngitis.

Dipstick

Blood	3+
Protein	2+
Leukocyte esterase	Negative
Nitrites	Negative

Microscopy

Dysmorphic red cells
Red cell casts
No crystals

Which single microscopy finding localizes the bleeding to the glomerulus?

The sediment after the arrest

Two days after a prolonged hypotensive episode in theatre, the creatinine is climbing and the urine output falling.

Dipstick

Blood	trace
Protein	1+
Leukocytes	negative
Nitrites	negative

Microscopy

Muddy brown granular casts, numerous
Renal tubular epithelial cells, occasional
No red cell casts, no dysmorphic red cells

Urine chemistry

Urine Na	68 mmol/L
FENa	2.8%

What does this sediment say about the mechanism of the AKI?

Dipstick blood, empty microscopy

The 79-year-old from the rhabdomyolysis lab case: dark urine after fourteen hours on the floor.

Dipstick

Blood	3+
Protein	1+
Leukocytes	negative
Nitrites	negative

Microscopy

No red cells seen
Pigmented granular casts
No red cell casts

How is a strongly heme-positive dipstick reconciled with a microscopy showing no red cells?

Frothy urine and swollen ankles

A 52-year-old with type 2 diabetes noticed frothy urine for months, and now ankle swelling to mid-shin. Albumin 24 g/L, creatinine 110.

Dipstick

Protein	4+
Blood	negative
Glucose	2+
Leukocytes	negative
Nitrites	negative

Microscopy

Oval fat bodies and fatty casts under polarized light ('Maltese crosses')
No red cell casts, no dysmorphic red cells

Heavy proteinuria, bland sediment, lipiduria, low albumin, edema. Which pattern is this, and what single quantification comes next?

Colic at four in the morning

A 38-year-old writhing with left loin-to-groin pain, vomiting, unable to lie still. Afebrile. Creatinine 96.

Dipstick

Blood	3+
Protein	trace
Leukocytes	negative
Nitrites	negative

Microscopy

Abundant non-dysmorphic (isomorphic) red cells
Occasional calcium oxalate crystals (envelope-shaped)
No casts

Which combination most raises the urgency in suspected ureteric colic?

The positive dipstick nobody was asking about

A routine dipstick on an 86-year-old with a long-term catheter, sent 'because it looked cloudy'. She is her usual self: comfortable, afebrile, eating breakfast.

Dipstick

Leukocytes	3+
Nitrites	positive
Blood	1+
Protein	trace

Microscopy

Numerous white cells and bacteria
No casts

Positive everything, asymptomatic patient, chronic catheter. What is the right move?