Cryptococcal Antigen Test

A cryptococcal antigen test is performed for diagnosing a cryptococcal infection or when an immunocompromised individual has the following symptoms of meningitis:

• Fever
• Headache
• Hallucinations
• Neck stiffness
• Nausea
• Vomiting
• Altered mental sensorium
• Mental confusion
• Sensitivity to light (photophobia)

Cryptococcal meningitis or cryptococcal infection is usually suspected in individuals with a compromised immune system due to HIV infection, liver cirrhosis, uncontrolled diabetes, lymphoma, leukaemia or sarcoidosis or in case of organ transplant.
In addition, a cryptococcal antigen test is also performed as a screening test in immunocompromised individuals with the following criteria:

• HIV/acquired immunodeficiency syndrome (AIDS) 
• Initiation of antiretroviral therapy (ART) for HIV 
• CD4-positive cell count of <200
• Oral thrush (candidiasis)

No special preparations are needed for this test.

Blood or cerebrospinal fluid (CSF) is used for evaluating the presence of cryptococcal antigen.

Blood test: Blood collection is a simple procedure in which a blood sample is drawn from a vein in the arm using a needle.

There is a minimal risk of pain, light-headedness and bruising at the site of injection associated with the test. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of blood withdrawal.

CSF collection: Collection of CSF may require a lumbar puncture (spinal tap), ie, removal of spinal fluid from the spine using a needle. A local anaesthetic agent is injected before the procedure; a spinal needle is inserted in the lower back area (lumbar), and about 5-10 millilitres (mL) of the sample is collected in four vials. After sample collection, the needle is removed, and the area is covered with a bandage. 

Lumbar puncture carries a risk of bleeding into the spinal canal or around the brain (subdural hematoma) and pain or discomfort during the test or infection at the site of puncture. CSF may leak from the punctures site (and can cause headache).

Normal results: Absence of cryptococcal antigen in patient samples indicates normal results, which means either they don't have a cryptococcal infection (meningitis) or some other pathogen is the cause of meningitis (in an immunocompromised patient).

Abnormal results: Presence of cryptococcal antigen indicates that the cause of meningitis is Cryptococcus.

Cryptococcal meningitis has a very high death rate as the disease progresses rapidly in a short span. However, according to the Center for Disease Control, this mortality can be prevented in patients who have already been diagnosed with HIV or have started ART. 

The World Health Organisation recommends the implementation of a cryptococcal screening program as a strategy to prevent death. This screening is mainly performed in individuals with low CD4-positive cells (<200 cells), advanced HIV infection or developed AIDS and those on ART or who have developed oral thrush (candidiasis) since these individuals are more prone to develop cryptococcal meningitis.

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.