Interpretation of the Urinalysis (Part 2) - The Dipstick

Overview of Urine Dipstick Testing

• Purpose: Quick semi-quantitative assessment of urine contents.

• Components: Reagent strips with pads for various tests; the contents tested can vary slightly by manufacturer.

How to Use a Urine Dipstick

• Testing Method:

  • Dip strip directly into urine or use a pipet to soak.

  • Wipe excess fluid.

  • Wait a predetermined time (generally 30 seconds to 2 minutes depending on the test).

  • Compare color changes on pads against provided standards.

  • Order of tests on strip reflects the duration required for each reaction.

Tests on the Urine Dipstick

Specific Gravity

• Definition: Measure of urine density relative to water.

• Normal Range: 1.001 to 1.035, reflecting hydration status.

• Key Insights:

  • Urine osmolality approximated by specific gravity - 1.035.

  • Low Specific Gravity (1.001): Indicates excessive hydration (e.g., diabetes insipidus).

  • High Specific Gravity (1.035): Indicates dehydration, SIADH, or the presence of glycosuria.

  • Fixed specific gravity around 1.010 suggests advanced kidney failure.

pH Level

• Range: Normal urine pH from 4.5 to 8.0, detecting lower limit often at 5.0 in dipsticks.

• Significance:

  • Determines conditions like renal tubular acidosis and helps in drug elimination.

  • Differentiates kidney stones based on acidity.

• Interpreting Abnormal pH:

  • Low pH (<5): Acidemia due to hypoventilation or lactate/ketone production.

  • High pH (7-8): Alkalemia, renal tubular acidosis, or infections with urease-producing bacteria.

  • Diet affects urine pH; cannot infer acid-base status without additional context.

Glucose

• Context: Normally filtered and reabsorbed by kidneys.

• Glycosuria: Detectable presence of glucose in urine, typically indicates serum hyperglycemia.

• Potential causes:

  • Proximal tubular dysfunction (e.g., Fanconi syndrome).

  • Genetic defects in glucose transport.

Hematuria

• Definition: Presence of blood in urine.

• Causes of Detection:

  • Sensitive to hemoglobin; can indicate muscle breakdown (rhabdomyolysis) or urinary tract bleeding.

  • Contamination with semen can lead to false positives.

Proteinuria

• Sensitivity: Sensitive mainly to albumin.

• Conditions Indicating Protein Presence:

  • Glomerular diseases (e.g., diabetic nephropathy).

  • Overflow proteinuria from conditions like multiple myeloma.

  • Post-renal proteinuria due to issues downstream in the GU tract.

Leukocyte Esterase and Nitrites

• Function: Used to diagnose urinary tract infections (UTIs).

• Leukocyte Esterase:

  • Indicates white blood cell enzyme activity, suggesting inflammation.

• Nitrites:

  • Detects bacteria in urine (Enterobacteriaceae family), converting nitrates to nitrites.

  • A negative nitrite test can occur due to insufficient bacterial action, low urine pH, or decreased nitrate excretion.

Ketones

• Components: Beta-hydroxybutyrate, acetoacetate, acetone.

• Usefulness: Indicates ketosis or ketoacidosis, primarily in diabetes; however, urine dipstick primarily detects acetoacetate and acetone.

• Potential for misleading results during ketoacidosis treatment, as undetected beta-hydroxybutyrate will convert, showing negative to positive ketone results upon improvement.

Bilirubin and Urobilinogen

• Bilirubin: Produced from hemoglobin breakdown, conjugated in the liver.

  • Positive in biliary obstruction; negative in hemolysis due to effective liver function.

• Urobilinogen: Formed from bilirubin in the gut, with variations in urine based on hepatic or biliary issues.

• Clinical Utility: Limited; many labs do not report bilirubin and urobilinogen.

Conclusion

• Summary: Assessing urine dipstick tests provides significant information on various conditions, though some tests have limited sensitivity or specificity.

• Next Steps: Upcoming part focuses on urine microscopy and overall summary.