Negative stain

Your doctor may order a negative stain when he/she suspects that you are suffering from an infectious disease. Though a lot of pathogenic microbes can be checked for using this test, here are some of the microorganisms that are commonly tested using negative staining along with the symptoms they cause. 

• C. neoformans - a fungus that causes cryptococcal meningitis - an inflammatory condition of the protective layer of the brain and spinal cord. Cryptococcal meningitis is more common in individuals with weakened immunity such as HIV or AIDS patients.

A cerebrospinal fluid (CSF, a fluid present in the brain and the spinal cord) sample is used to detect C. neoformans. Symptoms of cryptococcal meningitis include:

• Headache
• Confusion, hallucinations and personality changes
• Lethargy
• Sensitivity to light
• Fever
• Stiff neck 

If untreated, cryptococcal meningitis may lead to:

• Coma
• Hearing loss
• Hydrocephalus (water on the brain)

Your doctor may order this test to check for different viruses that cause rashes. For example: 

• Varicella-zoster virus - the causative agent of chickenpox and shingles.

You may have the following symptoms in chickenpox infection:

• Itchy blisters
• Rashes, which may appear in three phases:
  • Red bumps
  • Blisters filled with some fluid (vesicles)
  • Broken blisters covered with crusts
• Fever
• Loss of appetite
• Headache
• Tiredness and feeling of being unwell

In shingles, a person may experience pain and burning sensation along with rashes. A shingles rash typically may show the following characteristics:

• Itching
• Rash on the face and ear
• Red patches
• Blisters filled with fluid

Poxviruses - cause various infections in humans and animals such as smallpox, monkeypox and orf.

Some of the symptoms related to monkeypox are:

• Fever
• Backache
• Chills
• Fatigue 
• Headache
• Muscle aches
• Rash or lesion

Infections due to other viruses such as orf virus may also show some symptoms similar to that of monkeypox virus infection, such as mild fever or fatigue.

• Herpes simplex virus - causes oral and genital herpes. Oral herpes causes cold sores whereas genital herpes is a sexually transmitted disease.

A herpes infection by the herpes simplex virus may show the following symptoms:

• Pain or itching
• Sores
• Small red bumps
• Ulcers 
• Crusts

Spirochetes - slender and curved spiral-shaped bacteria with high motility, for example, the Treponema species. One of the species of Treponema, Treponema pallidum, is responsible for syphilis, a sexually transmitted disease in humans.

Some of the symptoms related to syphilis are:

• Sores around or in the mouth, vagina or penis
• Fever
• Loss of appetite
• Patches on the genitals or skin folds
• Skin rashes on the palms and soles
• Vision changes

The preparation of the test depends on the type of sample that is ordered by the doctor.

If a biopsy sample is required, inform your doctor about any medication that you might be consuming, which may even include vitamin and supplements, over-the-counter medicines or herbal remedies. Also, let your doctor know if you have any bleeding problem or allergies or if you are consuming blood-thinning medications such as aspirin or warfarin.

You may be required to empty your bowel or bladder before taking a CSF sample.

A CSF sample is required to check for Cryptococcus. The sample is drawn by a method called spinal tap or lumbar puncture. The sample collection will be done in the following manner:

• Your healthcare practitioner will ask you to sit or lie on your side on the examination table. 
• They will clean your back using an antiseptic solution and numb the area by injecting an anaesthetic into your skin.
• When the area is numb, they will insert a lumbar puncture needle between the two small backbones of your lower spine. 
• A small amount of fluid will be collected and sent to the laboratory for testing.
• After the procedure, you may be asked to lie on your back for at least an hour to avoid having a headache later.

If a vesicle sample is needed (for example from chicken pox), the following procedure may be used:

• The laboratory technician will remove the surface of the vesicle using a sterile needle.
• He/she will vigorously swab on the base of the lesion with the help of a sterile swab. This is done to collect infected cells and fluids.
• The sample will be immediately sent to the laboratory for testing.

A crust sample is directly removed from the skin and sent to the laboratory for testing.

A biopsy sample may sometimes be needed, which may be drawn by in the following manner:

• The doctor will numb the area of the skin before the procedure. 
• If an outer layer is to be tested, he/she will scrape or remove it using a small razor.
• For a deep layer sample, a punching tool is used to remove a small area (the size of a pencil eraser) of tissue. The area is later closed by applying stitches. 
• The procedure will be completed in 15 minutes.

Normal results:

A normal result is reported as negative. It indicates that no infectious microbe was detected in the given sample. 

Abnormal results:

An abnormal result is reported as positive. The laboratory technician will interpret the results depending on the size and shape or the structure of the microorganisms. For example, an orf virus may be observed as ovoid with a criss-cross arrangement on the surface.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.