Urine Dipstick Test

What is a Dipstick Test?

Method / How to Perform

1. Test urine as soon as possible after collection (cells sink rapidly).
2. Immerse the strip completely in urine for 1 second or less.
3. Draw the edge of the strip along the rim of the container and lightly tap to remove excess urine (prevents reagents from mixing between pads).
4. Hold the strip horizontally or place on a clean gauze until the recommended reading time elapses.
5. Read results at 1-2 minutes by comparing colors to the manufacturer's chart. Automated readers can also be used.

• Roberts and Hedges' Clinical Procedures in Emergency Medicine

Parameters Tested (Standard 10-Parameter Strip)

How to Quantify / Interpret Results

1. Protein

• The strip is highly sensitive to albumin (glomerular proteinuria) but insensitive to globulins, Bence Jones protein, or hemoglobin.
• A dipstick-negative but sulfosalicylic acid (SSA)-positive result is suspicious for light chain (Bence Jones) proteinuria.
• Positive results should be confirmed with a urine protein:creatinine ratio or albumin:creatinine ratio on a fresh morning specimen.
• False positives: alkaline urine (pH >7), chlorhexidine contamination, phenazopyridine.
• False negatives: very dilute urine, low pH, non-albumin proteinuria.
• National Kidney Foundation Primer on Kidney Diseases, 8e; Textbook of Family Medicine 9e

2. Blood

• Detects RBCs, free hemoglobin, and myoglobin (all have peroxidase activity).
• Very sensitive: positive with as few as 10 RBCs/mL.
• Discrete dots (speckled pattern) on the pad = non-hemolyzed intact RBCs.
• Uniform color change = hemoglobin or myoglobin.
• Confirmed by microscopy: dipstick-positive but no RBCs on microscopy suggests hemoglobinuria or myoglobinuria.
• Sensitivity of only ~14% for rhabdomyolysis-level myoglobinuria (CPK up to 1000 U/L).

3. Leukocyte Esterase (LE)

• Detects enzymes from neutrophil granules - a proxy for pyuria.
• Reported as: Negative / Trace / 1+ / 2+ / 3+
• Sensitivity for UTI: 50-96% (summary estimate ~79%); Specificity: 87-99%.
• Most common false positive: vaginal contamination.
• Detection threshold: ~10-100 WBCs/µL urine.

4. Nitrites

• Gram-negative enteric bacteria reduce dietary nitrates to nitrites.
• Reported as: Positive / Negative (qualitative).
• High specificity (~95-98%), low sensitivity (~45-50%) - a positive is highly meaningful, but a negative does NOT rule out UTI.
• Best done on first morning urine (requires several hours of bladder dwell time for conversion).
• Combined LE + Nitrite positive: sensitivity 88%, specificity 79% for UTI.

5. Glucose

• Glucose oxidase reaction; normally negative.
• Reported semi-quantitatively as: Negative / Trace / 1+ / 2+ / 3+
• Glucose spills into urine when serum glucose exceeds approximately 180-200 mg/dL (renal threshold).
• Glycosuria without hyperglycemia suggests renal tubular dysfunction.

6. Ketones

• Detects acetoacetate (5-10x more sensitive than to acetone); does not detect beta-hydroxybutyrate (which accounts for 80-95% of total ketones in ketoacidosis).
• Reported as: Negative / Trace / Small / Moderate / Large
• Seen in: DKA, starvation, alcoholic ketoacidosis, isopropyl alcohol ingestion.
• Urine ketone testing is more sensitive than serum ketone testing.

7. Specific Gravity (SG)

• Reflects ionic strength of urine using indicator dyes with ionic strength-dependent pKa.
• Range: 1.003 (dilute) to 1.030 (concentrated); isosthenuria (fixed 1.010) is seen in chronic kidney disease.
• Note: SG strips do not detect glucose or nonionic radiographic contrast agents (unlike refractometry or urinometry).

8. pH

• Measured by multi-indicator dyes; range 4.5-8.0.
• Normal is approximately 5-6 (acidic, due to net acid excretion).
• Alkaline urine (>7): vegetarian diet, post-meal "alkaline tide," urease-splitting organisms (e.g., Proteus), renal tubular acidosis.
• Inappropriately high pH in metabolic acidosis suggests distal RTA.

9. Bilirubin

• Detects only conjugated (direct) bilirubin - reflects hepatocellular disease or biliary obstruction.
• Bilirubinuria appears before clinical jaundice.
• Unconjugated bilirubin is protein-bound and does not pass the glomerulus - so prehepatic jaundice is bilirubin-negative.

10. Urobilinogen

• A small amount is normally present (formed from bilirubin breakdown in the gut).
• Elevated: hemolysis, hepatocellular disease (hepatitis, cirrhosis).
• Absent: complete biliary obstruction (no bilirubin reaches the gut).

• Roberts and Hedges' Clinical Procedures in Emergency Medicine, Table 67.4

Summary: How Results Are "Quantified"

• Qualitative (positive/negative): Nitrites, Bilirubin
• Semi-quantitative (graded scale): Protein (Trace, 1+, 2+, 3+, 4+), Blood (Trace-3+), LE (Trace-3+), Ketones (Trace to Large), Glucose (Trace-3+)
• Numeric scale: pH (4.5-8.0), Specific Gravity (1.003-1.030)

• 24-hour urine protein or spot urine protein:creatinine ratio (for proteinuria)
• Urine culture (for suspected infection)
• Urine microscopy (for hematuria, casts)
• Urine albumin:creatinine ratio (for microalbuminuria/CKD monitoring)
• Urine myoglobin assay (if rhabdomyolysis suspected)
• Comprehensive Clinical Nephrology 7e; Harriet Lane Handbook 23e