AUBF: Physical Examination of Urine Reviewer

AUBF: Physical Examination of Urine — Reviewer

OVERVIEW

Physical examination of urine includes color, clarity, and specific gravity — the only parameters in routine urinalysis (physical examination). Think of it as the screening phase, while chemical and microscopic exams are the confirmatory phase. Findings should always correlate with chemical and microscopic results.

1. URINE COLOR

Normal Urinary Pigments

Pigment

Description

Urochrome

Main pigment; causes yellow color; product of endogenous metabolism produced at a constant rate. Dilute = pale yellow; Concentrated = dark yellow. Increased in thyroid conditions and fasting states.

Uroerythrin

Pink pigment; binds to urate crystals; most evident in refrigerated specimens; gives a pink "brick dust" color to sediment

Urobilin

Oxidation product of urobilinogen; imparts orange-brown color to urine that is not fresh

Abnormal Urine Colors

A. Dark Yellow / Orange / Amber

  • Bilirubin → perform foam shake test: yellow foam = bilirubin; white foam = albumin; no foam = normal. Bilirubin converts to biliverdin → urobilinogen (no foam) — be time-sensitive!

  • Phenazopyridine (Pyridium) → UTI medication; thick orange pigment; interferes with chemical tests; produces yellow foam (can mimic bilirubin)

  • Other meds: sulfasalazine, some laxatives, chemotherapy drugs

B. Red / Pink / Brown (Red = most common abnormal urine color)

Cause

Notes

Blood (RBCs)

Most common abnormal cause; color ranges pink to brown depending on amount, pH, and contact time

RBCs in acidic urine (prolonged)

Hgb → methemoglobin (brown) = glomerular/UPPER tract bleeding; fresh RBCs = LOWER tract bleeding

Porphyria

Oxidation of porphobilinogen → porphyrins → port wine urine

Menstrual contamination

Most common non-pathologic cause; check 3–5 days after menstruation

Beets

In genetically susceptible individuals in alkaline urine

Blackberries

In acidic urine

Medications

Rifampin, phenolphthalein, phenindione, phenothiazines

3 Causes of Red Urine that test (+) for blood:

  • Hematuria → Red & CLOUDY

  • Hemoglobinuria → Red & CLEAR

  • Myoglobinuria → Red & CLEAR

Differentiate via: (1) Clarity, then (2) 2.8g Ammonium Sulfate Test

  • Hemoglobinuria → RED supernatant + NO precipitate

  • Myoglobinuria → Clear supernatant + RED precipitate

C. Brown / Black

Cause

Notes

Melanin

Oxidation product of melanogen; excess in malignant melanoma; turns black on exposure to air

Homogentisic acid

Metabolite of phenylalanine; turns black in alkaline urine; seen in alkaptonuria; turns black without air exposure (standing at room temp)

Medications

Antimalarials, levodopa, methyldopa, metronidazole, nitrofurantoin, laxatives

Non-pathologic

Fava beans, rhubarb, aloe

Differentiation: Alkaptonuria → black without uncapping; Melanoma → black once exposed to air

D. Blue / Green / Purple

Cause

Notes

Pseudomonas infection

Pathological

Blue diaper syndrome (Drummond's syndrome)

Malabsorption of tryptophan → converted to indican by bacteria; X-linked; associated with Hartnup disease

Indican / Klebsiella, Providencia

Purple staining in catheter bags

Non-pathologic

Breath deodorizers (Clorets), food dye, B vitamins, asparagus

Medications

Methylene blue, methocarbamol, indomethacin, amitriptyline, propofol

2. URINE CLARITY

Determined by holding the specimen in front of a light source against a printed background in a clear container.

Clarity Terminology

Term

Description

Clear

No visible particles; transparent

Hazy

Few particulates; print easily seen through urine

Cloudy

Many particulates; print blurred through urine

Turbid

Print cannot be seen through urine

Milky

May precipitate or be clotted

Note: "Hazy" was formerly termed "slightly cloudy"

Normal Clarity

  • Freshly voided urine is usually clear (especially midstream clean catch)

  • Amorphous phosphates/carbonates → white cloudiness in alkaline urine

Non-Pathologic Causes of Turbidity

  • Squamous epithelial cells and mucus (especially in females)

  • Improper preservation → bacterial growth

  • Refrigerated specimens:

    • Amorphous phosphates/carbonates → white precipitate (alkaline pH)

    • Amorphous urates → pink "brick dust" precipitate (acidic pH)

  • Other: mucus, crystals, semen, fecal contamination, radiographic media, talcum powder, vaginal creams

How to differentiate refrigerated precipitates via pH:

  • Alkaline → Amorphous phosphates

  • Acidic → Amorphous urates

Pathological Turbidity

  • Most common: RBCs, WBCs, bacteria

  • Less common: non-squamous epithelial cells, yeast, trichomonads, abnormal crystals, chyluria (lymph fluid), lipiduria

The amount of turbidity should correspond with microscopic findings. Clear urine is not always normal.

3. URINE ODOR

(NOT part of routine urinalysis — seldom of clinical significance)

  • Normal: faint aromatic odor when fresh; ammonia smell develops as urea breaks down on standing

  • No odor = possible underlying condition (e.g., Acute Tubular Necrosis / Acute Renal Failure)

Abnormal Odors

Odor

Condition/Cause

Foul, Ammonia-like

Bacterial decomposition, UTI

Fruity, Sweet

Ketones — DM, starvation, vomiting/diarrhea

Maple Syrup

Maple Syrup Urine Disease

Mousy / Barny / Musty

Phenylketonuria

Rancid

Tyrosinemia

Sweaty Feet / Acrid

Isovaleric Acidemia & Glutaric Acidemia

Rancid Butter / Fishy

Hypermethioninemia

Rotting / Old Fish

Trimethylaminuria

Bleach

Contamination/adulteration of specimen

Menthol-like

Phenol-containing medications

Rotten Eggs

Cystinuria

Swimming Pool

Hawkinsinuria

Cat Urine

3-hydroxyl-3-methylglutaric aciduria

Tomcat Urine

Multiple decarboxylase deficiency

No Odor

Acute Tubular Necrosis / Acute Renal Failure

Pungent, Fetid

UTI; ingestion of onions, garlic, asparagus (methylmercaptan)

Food-related: Onions, garlic, and asparagus can cause pungent odor. Notably, only genetically predisposed individuals can smell the asparagus odor.

⭐ QUICK MEMORY AIDS

  • Urochrome = yellow | Uroerythrin = pink (brick dust) | Urobilin = orange-brown

  • Yellow foam = bilirubin | White foam = albumin | No foam = normal

  • Cloudy red = hematuria | Clear red = hemoglobinuria or myoglobinuria

  • Ammonium sulfate test precipitates myoglobin

  • Alkaline pH → amorphous phosphates | Acidic pH → amorphous urates

  • Alkaptonuria → black without air | Melanoma → black with air