Urinalysis reagent strips, often called dipsticks, function as a quick chemical screening tool to provide preliminary insights into a person’s health. They are narrow plastic strips with small absorbent pads, each containing specialized chemicals that react to various compounds found in urine. This non-invasive method is frequently used to screen for conditions affecting kidney function, the urinary tract, and metabolic disorders like diabetes. Accurate results rely heavily on precise reading and interpretation of the resulting color changes.
Preparing and Conducting the Test
Obtaining a reliable result begins with proper sample collection, typically requiring a fresh, clean-catch urine specimen to minimize contamination from the surrounding area. Once the sample is collected, the test strip must be quickly and fully immersed, ensuring all chemical pads are saturated. Immediately upon withdrawal, gently draw the strip’s edge against the container rim to remove excess fluid. This prevents chemicals from adjacent pads from mixing, which could lead to inaccurate color development.
Precise timing is required because the chemical reactions on each pad develop colors at different rates. Most test pads require reading within a specific window, often ranging from 30 seconds to two minutes, depending on the substance being tested. Following the manufacturer’s instructions for the exact timing of each pad is necessary, as colors appearing after the recommended period are not diagnostically meaningful.
Interpreting the Color Chart and Measurements
Reading a reagent strip involves comparing the colors that develop on the strip’s pads to the corresponding color chart printed on the product container. Each pad detects a different component, and the intensity of the resulting color corresponds to the concentration of that substance. For accurate comparison, the strip should be held horizontally and matched to the chart under good lighting conditions to avoid misinterpreting subtle color variations.
One pad measures Glucose, which is typically not detectable in normal urine; a color change indicates its presence. Elevated glucose levels suggest high blood sugar, often associated with diabetes or impaired glucose handling by the kidneys. The Protein pad is another indicator, normally negative. A color change, often turning green, suggests the presence of protein, which can signal potential kidney disease or damage.
The pH pad measures the acidity or alkalinity of the urine, with a normal range generally falling between 5.0 and 7.5. A reading below this range suggests highly acidic urine, while a higher reading indicates alkaline urine. Both extremes can reflect dietary factors or suggest conditions like a urinary tract infection. The color change intensity is matched to a semi-quantitative scale on the chart, allowing estimation of the substance level, such as trace, moderate, or large amounts.
Factors Affecting Test Reliability
Several factors unrelated to the patient’s health can compromise the accuracy of reagent strip readings, starting with the physical condition of the strips. Improper storage, such as exposure to moisture, excessive heat, or light, can degrade the chemical reagents, leading to inaccurate results. Using strips past their expiration date or those from a bottle left uncapped for an extended time will also yield unreliable readings.
Contamination of the urine sample is another common issue that can skew the test results. For example, the presence of menstrual blood or vaginal discharge can cause false positive readings for blood and leukocyte pads, making interpretation misleading. Furthermore, high concentrations of ascorbic acid, commonly found in the urine of people taking Vitamin C supplements, can interfere with the chemical reactions, sometimes causing false negative results for glucose and blood.