What Happens During a River Blindness Skin Snip Test?
At a Glance
A skin snip test for river blindness is a quick, bloodless procedure that takes tiny, shallow skin samples, usually from the hips or buttocks. The sample is placed in saline for up to 24 hours to see if microscopic worms emerge. This test is the best way to confirm an active infection.
A skin snip test is the traditional gold-standard method for diagnosing onchocerciasis (river blindness) by looking for the parasite’s larvae (microfilariae) directly in your skin [1]. While the idea of a “snip” or biopsy might sound intimidating, the procedure is very quick and takes only a tiny, superficial piece of skin [2].
The Procedure: Step-by-Step
When you have a skin snip test, your doctor will collect small skin samples from specific areas of your body where the parasites are most likely to gather. The most common spots are the hips (iliac crests), the buttocks (gluteal folds), or sometimes the shoulders and calves [3] [4]. Usually, doctors will take several snips (often two to four) to ensure the test is as accurate as possible [4].
To take the sample, your doctor will use either a specialized instrument called a scleral punch or a sterile scalpel [5] [6]. A scleral punch works a bit like a tiny hole puncher. If a scalpel is used, the doctor will usually gently lift the top layer of the skin with a needle and carefully slice off the tiny raised piece [7].
Because the sample taken is extremely shallow and bloodless, the procedure is usually done without anesthesia [2]. A numbing shot (like lidocaine) is typically not used because the burning of the injection itself would actually cause more discomfort than the quick, nearly painless pinch of the test itself [3] [8].
It is very important that this snip is bloodless [2]. If blood mixes with the sample, it can obscure the view under the microscope and accidentally introduce other blood-borne parasites (such as Loa loa) that confuse the diagnosis [9] [7]. Because the snips are so superficial, they require minimal aftercare and heal quickly [2].
Analyzing the Sample
Once the skin sample is collected, the doctor or lab technician does not look at it immediately. Instead, the tiny piece of skin is placed in a small dish filled with saline (saltwater) or a similar liquid [1] [10].
The sample sits in this fluid at room temperature [10]. If you are infected with the Onchocerca volvulus parasite, the microscopic worms (microfilariae) will begin to emerge from the skin tissue and swim out into the saline [11]. While the idea of worms swimming out of your skin might sound terrifying, these microfilariae are completely invisible to the naked eye—you will not feel them leaving the sample, and you will not see them in the dish [1] [11].
You will not need to wait in the clinic while this happens. Initial results may be ready in a few hours, but the sample is typically left for up to 24 hours to give the microscopic worms plenty of time to emerge [1] [12]. After this incubation time, the technician examines the fluid under a microscope to count any worms that have appeared [1].
Modern Testing Enhancements and Alternatives
While examining the saline under a microscope is standard, the worms can sometimes be hard to find if you have a mild infection or have recently taken anti-parasitic medication like ivermectin [13]. Because of this, labs sometimes run advanced molecular tests, such as PCR (Polymerase Chain Reaction), on the skin snips [12]. PCR looks directly for the parasite’s DNA and is much more sensitive than relying solely on a microscope [14].
Patients often ask if they can choose a rapid blood test instead of a skin snip to avoid the biopsy altogether. While rapid, less invasive blood tests that look for antibodies are increasingly used, they generally tell doctors if you have ever been exposed to the parasite at some point in your life [15] [16]. The skin snip test, particularly when combined with PCR, remains an important tool to confirm if you have an active, current infection that requires treatment right now [12] [16].
Common questions in this guide
Does a skin snip test for river blindness hurt?
Where on the body are skin snips taken?
How long does it take to get results from a skin snip test?
Why can't I just get a blood test for river blindness?
Will I see worms swimming out of my skin during the test?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.Which areas of my body will you be taking the skin snips from?
- 2.How many skin samples do you plan to take to ensure the test is accurate?
- 3.Does your clinic rely on the microscope method, or will my skin snips also be sent for PCR (DNA) testing to ensure accuracy?
- 4.When should I expect to receive a phone call or message with my results?
- 5.What specific aftercare steps should I take to keep the biopsy sites clean and avoid infection?
- 6.Are there rapid blood tests we could consider alongside the biopsy to get a complete picture of my health?
Questions For You
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References
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This page provides educational information about diagnostic testing for river blindness. Always consult an infectious disease specialist or your healthcare provider for medical advice and accurate diagnosis.
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