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.

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.

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.

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.

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.

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.

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.

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.

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: 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.

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.