Histoplasma Complement Fixation
What is Histoplasma Complement Fixation?
Histoplasma complement fixation is a laboratory test used to help diagnose Histoplasma infections. This test involves mixing patient serum with Histoplasma antigens. A reactivity is then observed, which helps identify if antibodies are present. This test is usually ordered when a patient is having symptoms that could be indicative of a Histoplasma infection, such as a fever, chest pain, and coughing.
The patient should not eat or drink anything 8-12 hours prior to the laboratory test. A fasting sample is preferred for this test.
The patient's blood sample is mixed with Histoplasma antigens in the lab, and the reaction observed. An increase or decrease in the titer of the reaction (an increase or decrease in the complement component of the reaction) is diagnostic of the presence of antibodies. The increase or decrease in the titers tells the doctor whether the patient has been exposed to the Histoplasma organism.
The reaction is measured in Ωt units, which is a measure of the amount of complement that has adsorbed to the antigen.
There are two types of Histoplasma complement fixation tests: the single dilution test and the double dilution test.
Single Dilution Test
The single dilution test is the most commonly used Histoplasma complement fixation test. It is simple and inexpensive to perform and is used to detect recent or acute Histoplasma infections. In this test, the patient's serum is mixed with Histoplasma antigen and then observed for a reaction. A positive result is indicative of an infection.
Double Dilution Test
The double dilution test is the more an accurate test, as it is able to detect the presence of antibodies to Histoplasma even if the patient has a chronic infection and the antigen level is low. In this test, the patient's serum is first mixed with a normal serum to reduce the reactivity. Then, the mixture is further diluted with Histoplasma antigen. A positive result indicates the presence of antibodies.
The primary risk associated with the Histoplasma complement fixation test is that it can produce false-positive results. This is more likely to occur if the patient has been recently vaccinated against the organism, as vaccine-induced antibodies can create a similar reaction as a true infection.
The Histoplasma complement fixation test is used to help diagnose a Histoplasma infection. It is often ordered when a patient is experiencing symptoms that may indicate an infection, such as a fever, chest pain, and coughing.
The histoplasma complement fixation test is often ordered when a patient is experiencing symptoms of a Histoplasma infection. It is also useful in determining if a patient has been exposed to the organism or if the infection is chronic or acute.