P-II-29. Abnormal findings in urine tests

尿検査の異常所見と基準値

Reference Values

Glomerulus: GFR 120 mL/min (180 L/day) → Tubule: 178 L/day reabsorbed
Urine output: 1–1.5 L/day — Polyuria > 2 L/day, Oliguria < 0.5 L/day, Anuria < 0.2 L/day
Glucosuria: appears at blood glucose ~9–10 mmol/L (renal threshold)
Urine pH: 4–8
Specific gravity: 1.001–1.030, where 1.010 = isosthenuria (equal to plasma → neither concentration nor dilution)

Abnormal Findings

Smell: ammonia-like → food, infection, abscess
Turbidity: nubecula from proteins (Tamm-Horsfall protein / uromodulin), while true turbidity = cellular urine (pus, blood, crystals)
Proteinuria → foamy urine
Squamous epithelial cells (EPI): use midstream, not first stream. EPI also appears in bacterial infection → can interrupt urinalysis
Mucus → urinary tract irritation, bacterial infection

Urine Sediment (centrifuge)

RBC → hematuria, RBC casts → glomerulonephritis
WBC → pyuria → pyelonephritis (normal 0–12 WBC/μL)
Casts → proteinuria. ↓filtration pressure → protein precipitation → hyaline cast

Semiquantitative Urinalysis (test strip)

Shows concentration of substances via color change (biochemical reaction)
Also detects ascorbic acid. Ascorbate can interrupt the reaction → false negatives
Strip panel: bilirubin, urobilinogen (liver function), ketone, ascorbic acid, glucose (blood sugar balance), protein, RBC (Hb), pH, nitrite, leukocytes, specific gravity

Detailed causes of abnormal urine color are covered in the next topic (II-30).

一問一答

▶What is the normal glomerular filtration rate (GFR)?

About 120 mL/min (roughly 180 L/day of filtrate).

▶What is the normal daily urine output, and how are polyuria, oliguria, and anuria defined?

Normal is 1–1.5 L/day; polyuria >2 L/day, oliguria <0.5 L/day, anuria <0.2 L/day.

▶At what blood glucose level does glucosuria appear (renal threshold)?

Around 9–10 mmol/L.

▶What is the normal range of urine pH and specific gravity?

Urine pH 4–8; specific gravity 1.001–1.030.

▶What is isosthenuria, and what specific gravity defines it?

Urine with specific gravity ~1.010, equal to plasma, meaning the kidney is neither concentrating nor diluting urine.

▶Why does proteinuria cause foamy urine?

Excess protein lowers surface tension, producing persistent foam.

▶What is nubecula in urine, and what causes it?

A faint cloud from proteins such as Tamm-Horsfall protein (uromodulin); true turbidity instead reflects cells (pus, blood, crystals).

▶What do red blood cell (RBC) casts in urine indicate?

Glomerulonephritis (glomerular bleeding).

▶What does pyuria (white blood cells in urine) suggest?

Urinary tract infection, classically pyelonephritis (normal is 0–12 WBC/μL).

▶How do hyaline casts form?

Reduced filtration pressure allows protein (Tamm-Horsfall) to precipitate in the tubules, forming hyaline casts.

▶Why should a midstream urine sample be used?

To avoid contamination by squamous epithelial cells and flora from the initial stream, which can interfere with urinalysis.

▶How does a urine dipstick (test strip) work?

Reagent pads undergo biochemical colour changes proportional to the concentration of each substance.

▶How can ascorbic acid (vitamin C) affect urine dipstick results?

It can interfere with the reactions and cause false-negative results (e.g. for glucose or blood).

▶Which dipstick parameters reflect liver function?

Bilirubin and urobilinogen.

▶What does a positive urinary nitrite suggest?

A bacterial urinary tract infection (many bacteria convert nitrate to nitrite).

▶What does an ammonia-like smell of urine suggest?

It may reflect diet, infection, or an abscess.

▶What does true turbidity (cloudiness) of urine usually indicate?

Cellular content such as pus (leukocytes), blood, or crystals.

▶How is urine sediment examined?

The urine is centrifuged and the sediment (cells, casts, crystals) is examined microscopically.

▶What does hematuria (RBCs in urine) signify?

Bleeding somewhere in the urinary tract; RBC casts specifically localize it to the glomerulus.

▶Why can squamous epithelial cells interfere with urinalysis?

They indicate skin/genital contamination (or infection) of the sample, reducing its diagnostic reliability.