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Urinalysis & Body Fluids

Physical

Let’s pull back and look at the “big picture” of the physical examination of urine. Think of this as the first impression—it’s what your senses and basic measurements tell you before you even touch a reagent strip or a microscope. This initial assessment provides a crucial framework for interpreting everything that follows

Physical Examination of Urine

The physical examination is the first phase of any routine urinalysis. It involves visually observing the specimen’s color and clarity and then measuring its concentration, either by specific gravity or osmolality. While seemingly simple, these initial steps can provide immediate and valuable clues about the patient’s hydration status, metabolic function, and the potential presence of disease

Color and Clarity: The Visual Clues

Your eyes are the first tool in urinalysis. What you see can immediately suggest normal physiological states or point you toward significant pathology

  • Color: The normal yellow color of urine comes from a pigment called urochrome. The intensity of this yellow is a rough guide to the urine’s concentration—a pale, straw-colored urine is dilute, while a dark amber urine is concentrated. However, a whole spectrum of abnormal colors can appear, each telling a different story:
    • Red to Brown: This is a critical finding. If the urine is cloudy and red, it suggests the presence of intact red blood cells (hematuria). If it is clear and red, it points to either free hemoglobin (hemoglobinuria) or myoglobin (myoglobinuria)
    • Amber to Orange: A classic amber or orange-brown color that produces a yellow foam when shaken is a strong indicator of bilirubin, suggesting liver disease or biliary obstruction. A bright, viscous orange is the tell-tale sign of the drug phenazopyridine (Pyridium)
    • Brown to Black: A urine that darkens upon standing is a classic sign of alkaptonuria (homogentisic acid) or, in some cases, the presence of melanin, indicating metastatic melanoma
  • Clarity: This refers to the transparency of the specimen. A fresh, normal urine should be clear. Cloudiness, or turbidity, is caused by suspended particles. Recognizing the potential cause of turbidity is key
    • Non-Pathologic Cloudiness: Often caused by amorphous crystals (white phosphates in alkaline urine, pink urates in acid urine) that precipitate in a refrigerated sample. Benign squamous epithelial cells and mucus are also common causes
    • Pathologic Cloudiness: This is a much more significant finding. The most important causes are:
      • White Blood Cells (Pyuria): Indicates infection or inflammation
      • Red Blood Cells: Causes a cloudy, red appearance
      • Bacteria: Causes a uniform haze, pointing to a UTI
      • Lipids: Can create a “milky” appearance, a hallmark of the nephrotic syndrome

Specific Gravity and Osmolality: The Measure of Concentration

This measurement is a direct assessment of the kidney’s ability to perform one of its most essential functions: maintaining the body’s water balance. It reflects the kidney’s work in concentrating or diluting the glomerular filtrate

  • Physiology Link: The process is controlled by Antidiuretic Hormone (ADH). When the body is dehydrated, ADH is released, causing the kidneys to reabsorb water and produce a small amount of concentrated urine with a high specific gravity. When the body is well-hydrated, ADH is suppressed, and the kidneys excrete a large volume of dilute urine with a low specific gravity

  • Interpreting the Results

    • A normal random SG can range from about 1.005 to 1.030
    • High Specific Gravity (Hypersthenuria): Seen in dehydration, but also in conditions like Diabetes Mellitus, where the high concentration of glucose increases the urine’s density
    • Low Specific Gravity (Hyposthenuria): Seen with high fluid intake or in Diabetes Insipidus, a disease where ADH is absent or ineffective
    • Isosthenuria (Fixed at 1.010): This is a critical finding. It indicates severe renal damage where the kidneys have lost all ability to concentrate or dilute urine. The urine’s specific gravity is the same as the original plasma filtrate, signifying end-stage renal disease

  • Osmolality vs. Specific Gravity: While specific gravity measures density (influenced by the number and size of particles), osmolality measures only the number of particles. Osmolality is considered the more accurate, “gold standard” measurement of renal concentrating ability because it is not affected by large, non-ionic molecules like glucose or radiographic dye that can falsely elevate the specific gravity