Hemastix are diagnostic test strips designed for the rapid detection of blood. These strips offer a simple and quick method to indicate blood presence in various samples, making them a practical tool for initial screenings.
What Are Hemastix and How They Work
Hemastix are small, plastic strips with a chemically treated pad at one end. They are used for the rapid, qualitative detection of blood, indicating its presence rather than a precise quantity. The reactive area is typically yellow before use.
The mechanism relies on the peroxidase-like activity of hemoglobin (from red blood cells) or myoglobin (from muscle tissue). This activity catalyzes a reaction between an organic hydroperoxide and a chromogen, such as 3,3′,5,5′-tetramethylbenzidine (TMB). This reaction oxidizes the chromogen, producing a color change on the pad. A positive result is indicated by a color change, typically from green to blue, developing within five seconds if hemoglobin is present.
Common Applications and What They Detect
Hemastix primarily detect blood, specifically hemoglobin from red blood cells and myoglobin from muscle tissue. They are highly sensitive, capable of detecting minute amounts of blood, but cannot differentiate between human and animal blood.
Common applications include:
Urinalysis: Screening for blood in urine (hematuria), which can suggest kidney stones, infections, or other urinary tract issues.
Fecal Occult Blood Testing (FOBT): Screening for hidden blood in stool, an early indicator of gastrointestinal bleeding, potentially signaling conditions like peptic ulcers or colorectal cancer.
Forensic Science: Preliminary testing to detect bloodstains at crime scenes, even those not visible.
Veterinary Medicine: Used for similar diagnostic purposes in animals.
Understanding Results and Their Limitations
The intensity of the color change on a Hemastix strip generally correlates with the amount of blood present. However, it is a qualitative test, indicating presence or absence rather than a precise measurement. Users compare the resulting color to a chart provided with the strips for interpretation.
Hemastix provide an indication, not a definitive diagnosis. Further testing by healthcare professionals is necessary to confirm findings. False positive results can occur due to factors like chemical oxidants (e.g., bleach, rust), plant peroxidases (e.g., horseradish, tomatoes), or other animal sources (e.g., saliva, pus). Conversely, false negative results can arise if blood is exposed to extreme environmental conditions (e.g., high heat, prolonged ultraviolet light) or if the sample is very dilute. The test detects hemoglobin or myoglobin, but not necessarily intact red blood cells.