Urine Analysis Overview

Turbidity in Urine

Definitions and Concepts

  • Turbidity: Refers to the cloudiness or haziness of urine caused by the presence of particulates or substances.

  • "Port wine" urine: Indicates the presence of porphobilinogen oxidation, commonly associated with porphyrias.

Causes of Turbidity

Nonpathogenic Causes

  • Colors of Urine Related to Turbidity:
    • Brown/black urine:
    • If urine turns black after standing test is negative for blood, this indicates:
      • Melanin: Associated particularly with malignant melanoma.
    • Blue/green urine:
    • Due to oxidation of melanogen to melanin.
    • Homogentisic acid: Found in individuals with alkaptonuria, which causes the urine to appear black when alkaline.
    • Medications that can affect color:
      • Levodopa, phenol derivatives, flagyl can induce color changes.

Pathogenic Causes

  • Bacterial Infections:

    • Notable pathogens include:
    • Pseudomonas: Known to cause urinary infections.
    • Intestinal infections: Leads to the formation of indican that can oxidize to indigo blue.

  • Catheter Bag "Purple": May indicate an association with Klebsiella, Providencia, and indican.

  • IV Phenol Medications: Can result in green urine.

  • Methylene blue and other medications: Responsible for producing blue/green shifts in urine color.

Transparency of Specimen

  • Various definitions related to clarity:
    • Clear: No visible particulates, excellent visibility.
    • Hazy: Few particulates, print can still be seen easily.
    • Cloudy: Many particulates present, print appears blurred.
    • Turbid: Print cannot be seen due to opacity.
    • Milky: May precipitate or appear clotted.

Nonpathogenic Turbidity

  • Common scenarios resulting in turbidity:
    • Hazy female specimens: Often due to squamous epithelial cells and mucus.
    • Bacterial growth: Frequently observed in nonpreserved specimens.
    • Refrigeration: Can lead to the formation of amorphous phosphates (white) or urates (pink).
    • Contamination: Can arise from fecal matter, talc, semen, creams, or IV contrast media.

Pathologic Turbidity

  • Most common causes:
    • Presence of:
    • RBCs (Red Blood Cells)
    • WBCs (White Blood Cells)
    • Bacteria
    • Yeast
    • Nonsquamous epithelial cells
    • Abnormal crystals
    • Lymph fluid
    • Lipids
  • Clarity evaluation: Important for determining the need for microscopic examination of the urine sample.

Specific Gravity (SG)

  • Specific Gravity: A rough screen of renal concentrating ability and hydration status, influenced by Antidiuretic Hormone (ADH).
  • Definition: Density of urine compared to an equal volume of distilled water at the same temperature.
  • Methods/Instrument for Measurement:
    • Direct Methods:
    • Urinometer: Considered least accurate due to temperature correction and substance density.
    • Harmonic Oscillation Densitometry (HOD): A more precise method for measuring specific gravity in urine samples.