Cryptococci Antigen Serum

Submitted on March 27, 2012

Cryptococcus is a type of fungus, and in a culture it can grow in the form of fungus. There are two forms of this fungus, one which is produced through sexual reproduction is known as filobasidiella and the other which is replicated asexually is known as Cryptococcus. Cryptococcus is considered the imperfect form of the fungus and is highly infective.

Reasons for Cryptococci Antigen Serum

If cryptococcus neoformans enters the body through inhalation, it may cause pneumonia. In fact, the fungus may even reach the brain once they invade the body. After this invasion, they cause meningitis. Apart from affecting the lungs and the brain, Cryptococcus may also affect the skin, bone and viscera in other parts of the body.

Usually cryptococcosis occurs as a primary disease. However, in some cases, it may also occur as a secondary infection caused due to suppression of the immune system. Traditionally, cryptococcal infections were diagnosed using a stain test with India Ink. However, the cryptococcal serum antigen test has now replaced the old test. Since Cryptococcus is an extremely sensitive organism, it also requires an extremely sensitive test to measure it.


This test is conducted using titrations. Specimens which are positive are tittered and the highest values are reported. If the titer reports a value of 1:8 or higher, it is an indication of a severe infection. If the patient is symptomatic of disease, but the titers show a value which is less than 1:8, it is an indication of an infection which is present but is just at the beginning stage.

One thing which is important is that since the test is extremely sensitive, incorrect handling of the specimen can cause false positives. On an average, it is estimated that every third test is a false positive. A culture can help ascertain the results.


For this test, either a blood specimen or a sample of spinal fluid is required. Cryptococcal antigen in both blood serum and cerebrospinal fluid are tested for AIDS related therapy. About 5-10 ml of blood is required for the test, and if the test is conducted on the cerebrospinal fluid, about 2 ml of sample is required.

If there is a positive result for both serum antigen and antigen in the cerebrospinal fluid, almost 95% of such patients are diagnosed with cryptococcal meningitis. However, even a negative result in the test doesn’t completely rule out the advent of the infection. The antigen levels may decrease if the therapy is effective therefore the tests are also conducted in order to check the efficacy of the treatment.