MLPAO Urinalysis and Body Fluids Fundamentals Flashcards

Which crystal found in acidic urine has a characteristic coffin-lid (envelope) shape?

Answer: Calcium oxalate dihydrate crystals

Calcium oxalate dihydrate crystals have a characteristic octahedral (envelope or coffin-lid) shape and are found in acidic to neutral urine. They are the most common crystal in urine and are associated with high-oxalate foods, ethylene glycol poisoning, and calcium oxalate kidney stones. Calcium oxalate monohydrate crystals are ovoid or dumbbell-shaped.

What does proteinuria detected by dipstick primarily measure?

Answer: Primarily albumin (the indicator is more sensitive to albumin than other proteins)

The urine dipstick protein pad uses a pH indicator (tetrabromophenol blue) that is primarily sensitive to albumin due to the protein error of indicators principle. It may miss low-molecular-weight proteins like Bence Jones protein (immunoglobulin light chains). Sulfosalicylic acid (SSA) or total protein measurement detects all proteins.

What is the significance of finding white blood cell (WBC) casts in urine?

Answer: They indicate renal parenchymal inflammation, typically pyelonephritis or interstitial nephritis

WBC casts localize inflammation to the kidney (renal tubules), distinguishing upper urinary tract infection (pyelonephritis) or interstitial nephritis from lower UTI (cystitis). WBCs trapped in Tamm-Horsfall protein matrix form these casts within the renal tubules. Their presence warrants further investigation of renal parenchymal disease.

What is the normal urine pH range, and what conditions cause alkaline urine?

Answer: pH 4.5-8.0; UTI with urease-producing organisms, vegetarian diet, and stale specimens

Normal urine pH ranges from 4.5 to 8.0, with average around 6.0 (slightly acidic). Alkaline urine (>7.0) is seen with UTI caused by urease-producing organisms (Proteus), vegetarian diets, metabolic alkalosis, and old/improperly preserved specimens (bacterial conversion of urea to ammonia). Acidic urine is seen with high-protein diets and metabolic acidosis.

What does a positive urine glucose test indicate?

Answer: Glucosuria, which occurs when blood glucose exceeds the renal threshold (approximately 10 mmol/L) or the tubular reabsorption capacity is impaired

Glucose in urine (glucosuria) occurs when blood glucose exceeds the renal threshold for glucose reabsorption (approximately 10 mmol/L or 180 mg/dL). Common causes include diabetes mellitus (most common), gestational diabetes, and renal glucosuria (low renal threshold). SGLT2 inhibitor medications also cause glucosuria therapeutically.

What are hyaline casts and are they clinically significant?

Answer: They are composed of Tamm-Horsfall protein and can be found in small numbers in normal concentrated urine or after strenuous exercise

Hyaline casts are composed of Tamm-Horsfall mucoprotein secreted by renal tubular cells. A few hyaline casts can be found in normal concentrated urine and after exercise or dehydration. Large numbers may indicate renal disease. They are transparent and best seen under reduced light or phase contrast microscopy.