Reference Range

Old Content

Chlamydia trachomatis is a gram-negative, obligate intracellular parasite that is linked to several diseases. A properly obtained negative C trachomatis culture indicates the absence of infection with 100% specificity.^{[1, 2]}

New Content

Normal findings include a negative culture and the following antibody values.^[3]

Chlamydophila pneumoniae

IgG: < 1:64
IgM: < 1:10

Chlamydophila psittaci

IgG: < 1:64
IgM: < 1:10

Chlamydia trachomatis

IgG: < 1:64
IgM: < 1:10

Normal findings also include negative nucleic acid detection results.^[3]

Normal findings

A properly obtained negative culture establishes with 100% specificity that a C trachomatis infection is not present.^{[1, 2]}

Abnormal findings

A positive culture confirms a C trachomatis infection with sensitivity between 50-85%.^{[1, 2]}Nucleic acid amplification test (NAAT) has surpassed this as the criterion standard, with sensitivity ranging from 85-95% with 99-100% specificity.^{[2, 4]}In 2014, the Centers for Disease Control updated its 2002 recommendations regarding screening tests to detect C trachomatis. These include the use of NAATs to detect chlamydia.^[5]

Common diagnoses related to positive culture are as follows:

Trachoma
Neonatal conjunctivitis
Nongonococcal urethritis
Cervicitis
Salpingitis
Pelvic inflammatory disease (PID)
Endometritis
Acute urethral syndrome
Proctitis
Epididymitis
Pneumonia of newborns
Perihepatitis (Fitz-Hugh-Curtis syndrome; this is more commonly associated with gonorrhea)
Lymphogranuloma venereum (LGV)

Collection

Specimen

Epithelial cells can be taken from the eye, urethra (remove purulent exudate), endocervix (remove purulent exudate), and rectum. If the specimen is taken from the patient’s genital tract, inform the patient not to urinate 3-4 hours before the specimen is taken.^[1]Tell female patients not to douche for 24 hours before the test.^[1]

Container

Swab transport system with sucrose phosphate (2SP) transport medium.

Collection method

Obtain specimen from epithelial cells in the infected site. A Dacron-tipped or rayon-tipped swab is preferred; calcium alginate and cotton-tipped swabs can sometimes be toxic.^[6]Use a metal or plastic shaft because wood shafts are toxic to the organism.^{[6, 2]}

Urethral specimen: Insert the microbiologic transport swab 0.75 inches to 2 inches (2-5 cm) into the urethra. Extract specimen into 2SP transport medium.^[1]
Endocervix specimen: Use a microbiologic transport swab or cytobrush. Extract specimen into 2SP transport medium.^[1]
Throat, eye, nasopharynx, and/or aspirates from infants should be extracted into 2SP transport medium.^[1]
Rectum: Insert the microbiologic transport swab 2-3 cm into the anal canal; material must be obtained from all walls of the rectum.^[7]

Handling

The specimen should be sent to the laboratory at 39.4°F (4°C).^[1]If the time between specimen collection and inoculation into cell culture is more than 24 hours, freeze the 2SP transport medium and send it to the laboratory with dry ice.^[1]

Growing

The organism cannot be grown on an artificial medium. It can be grown on any of these cell lines treated with cycloheximide: McCoy, HEp-2, HeLa, or buffalo green monkey cells.^{[2, 6]}

Panels

A C trachomatis culture is typically performed for the following:

Sexual assault and/or child sexual abuse
Suspected urinary tract infection

Description

Chlamydia trachomatis is a small gram-negative, obligate intracellular parasite that is deficient in energy metabolism.^[2]Its host cells are primarily epithelial cells, which line the conjunctiva, respiratory tract, urogenital tract, and rectum.^[2]

Before PCR, cell culture was the criterion standard. Its use has since been marginalized due to its technical complexity, time and handling requirement, expense, and the difficult nature of the organism.^[2]The sensitivity of cell culture ranges from 50-70%.^[6]Due to this, NAAT’s has become the criterion standard because of its higher sensitivity (85-95%).^{[2, 6]}However, cell culture is routinely performed because of the high specificity, 100%, when properly obtained and using fluorescein-conjugated monoclonal antibodies during the staining phase.^{[6, 8]}

Although C trachomatis culture has a lower sensitivity compared to NAATs, maintaining the ability to perform this laboratory test is still important. The new Swedish variant of C trachomatis, which eluded NAATs, was detected because the organism could be cultured.^[7]

Indications/Applications

When diagnosis of C trachomatis is disputed, a culture should be performed.^[6]Additionally, the CDC recommends that a positive nonculture test should be verified if the false-positive could lead to adverse medical, social, or psychological consequences.^[6]Culture confirmation is preferred, however, if the nonculture test was a NAAT; they have stated a second NAAT will suffice in lieu of obtaining the culture.^[6]

The most common indications for obtaining a culture are in cases of suspected sexual assault, child sexual abuse, urinary tract infections, and susceptibility testing in the case of resistant organisms.

Additionally, the test could be performed for suspected trachoma, neonatal conjunctivitis, nongonococcal urethritis, cervicitis, salpingitis, pelvic inflammatory disease, endometritis, acute urethral syndrome, proctitis, epididymitis, pneumonia of newborns, perihepatitis (Fitz-Hugh-Curtis syndrome), and lymphogranuloma venereum. However, NAATs is most often used in these situations because of its quick turnaround and high sensitivity.^[6]

Considerations

Causes of false-positive readings are as follows:

Patient has used anti-C trachomatis drugs within a few days prior to collection.^[1]
Males voided within in 1 hour of specimen collection.^[1]
Females have douched within 24 hours.^[1]
Proper collection techniques could not be performed.^[1]
Contamination of the specimen due to fecal material in rectal culture.^[1]