Chlamydia is the most prevalent sexually transmitted infection (STI) in Europe and USA, and is progressively increasing [2, 3, 4, 5]. The World Health Organization estimates that 92 million new cases of Chlamydia occur worldwide every year [6] and it is the most common STI in teenagers [7]. Chlamydia can cause serious reproductive morbidity and is among the main causes of infertility or potentially fatal ectopic pregnancies [5, 8, 9, 10].

In women, untreated Chlamydia trachomatis that ascends from the endocervix to the upper genital tract can cause PID (Pelvic Inflammatory Disease), which can result in scarring and adhesions in the fallopian tubes and adnexae [5]. This increases the risk of ectopic pregnancy, tubal infertility and chronic pelvic pain [11].

In one study, 30% of women with untreated C. trachomatis developed PID, the majority of which had symptoms that were too mild or nonspecific to cause them to seek medical treatment. Regardless of symptom intensity, the consequences of untreated PID are severe: 20% of those with symptomatic PID might become infertile; 18% will experience debilitating, chronic pelvic pain, and 9% will have a life-threatening tubal pregnancy [12, 13, 14, 15]. However, if detected early, inexpensive and effective treatment is available.

While complete removal of Chlamydia infection isn’t always easy, after specialized treatment, patients get significantly improved chances of success in either natural or assisted reproduction attempts.


The Hidden-C® Test is far superior in overall performance compared with other C. trachomatis culture and non-culture diagnostic methods with respect to sensitivity, specificity, and ease of specimen transport. The use of menstrual tissue along with the Real-Time PCR method results in greatly expanded overall sensitivity of detection, above 95%, while maintaining very high specificity, usually ≥99% [1, 16].

Although still widely used by many laboratories, the outdated “classical” methods for Chlamydia screening and diagnosis including Direct fluorescent antibody (DFA) tests, Enzyme immunoassay (EIA) tests and Serology tests are no longer recommended, and their use is discouraged by the official guidelines in most countries including the US [16]. The performance of nucleic acid amplification tests such  as PCR is better than that of any of the other tests available for the diagnosis of Chlamydial infections.

Classical non-culture tests fail to detect a substantial proportion of infections in contrast to PCR that amplify and detect C. trachomatis– specific DNA sequences. PCR-based tests typically detect 20%–50% more Chlamydial infections than could be detected by culture or earlier non-culture tests [16]. As a result, Chlamydia infections that are localized in the upper genital tract, where they are often asymptomatic, often remain undetected and can lead to serious long-term health problems.


The Hidden-C® Test is a non-invasive diagnostic test and women can collect the menstrual blood specimen easily at home and retry if the first attempt fails. An additional advantage of this method is that it can be easily repeated and thus antibiotic therapy results can be monitored [17]. Specimen collection is passive (a few drops of menstrual fluid are collected into the container), guaranteeing a good quality sample without patient intervention and ensuring reproducibility of results.


The Hidden-C® Test Specimens can be self-collected by patients and shipped to the reference laboratory by post. This provides the most accessible and acceptable method for the patient and it does not require expensive facilities or trained staff [17].

It is also the only non-invasive method that allows detection of upper genital tract infection in virgin women and young women before they become sexually active.


The increased sensitivity and effectiveness of The Hidden-C® Test using self-collected menstrual fluid sample followed by real-time PCR analysis for the detection of Chlamydia trachomatis, has been shown in a published research study using menstrual tissue (blood) samples of 87 women with a background of infertility [1]. The results indicate a statistically significant increase in the prevalence of Chlamydia trachomatis (37%), where the specimen used was self- collected menstrual blood and the analysis was carried out by means of The Hidden-C® Test using our in-house real-time PCR, compared to the cases where the specimen used was cer vical/vaginal secretions and either analyzed by commercial PCR method (18.3%) or by culture/DFA (13.8%) (Fig.1).


Statistical analysis of menstrual fluid specimens collected by women with history of infertility from Greeceand the UK over a period between May 2010 and February 2011 (883 women in total) and analyzed by The Hidden-C® Test, revealed prevalence of Chlamydia infections in up to 39% of cases. Considering that the prevalence of Chlamydia infections among sexually active women aged 14-39 years during 2007-2012 was recorded to be less than 8% [5, 18], the outcomes of this study indicates that the current diagnostics methods underestimate the number of Chlamydia infections within the population. Our results are in consistence with previously published data indicating that Chlamydia infections have high prevalence rates in asymptomatic women [17, 19] and highlight the necessity to introduce a new, more sensitive and more practical diagnostic tests in preventive medicine of sexually transmitted infections.

Finally, according to our experience and results over the years we have reached the conclusion that chlamydia can also be non-sexually transmitted and this is supported by the fact that they have been found in virgin women and young women before they become sexually active and in one or both partners of strictly monogamous relationships.


  1. IN CASES OF COUPLES FACING UNEXPLAINED INFERTILITY, DIFFICULTY OF CONCEPTION, EARLY AND RECURRENT MISCARRIAGES: For best results, we recommend to use The Hidden-C® Test together with the The SPITM Test (the test for the investigation of the male reproductive system).
  2. FOR DIAGNOSIS OF ENDOMETRITIS AND PELVIC INFLAMMATORY DISEASE (and a wide range of other infections in addition to Chlamydia): The Hidden-C® Test can simultaneously detect, a wide array of pathogens, according to the needs of the patient or the referring clinician including Chlamydia spp., Ureaplasma spp., Mycoplasma spp. [1] and other bacteria, viruses and fungi by using a single menstrual blood specimen. In combination with conventional diagnostic methods such as cervical and vaginal cultures, microscopy, PAP smear test and gynecological examination, The Hidden-C® Test is suggested as a complementary diagnostic tool to monitor the female genitourinary system.
  3. BEFORE ANY KIND OF INVASIVE PROCEDURE OR SALPINGOGRAPHY (to prevent spreading of infection further up the genital tract): Infection diagnosis of the endometrium by The Hidden-C® Test should ideally take place before any invasive procedure or salpingography to minimize the risk of spreading an infection throughout the upper genital tract. Invasive procedures for the diagnosis of intrauterine infection such as endometrial biopsy may cause endometritis themselves, or exacerbate the condition as entering the uterus via the cervix can provide a point of entry for cervical/ vaginal bacteria.
  4. IN PREVENTIVE MEDICINE AND REPRODUCTIVE HEALTHCARE (for Chlamydia screening of the population): Due to its non-invasive nature and high patience acceptance, the Hidden-C® Test allows Chlamydia testing for preventive screening, without the practical problems associated with invasive diagnostic methods, before a chronic infection leads to irreversible or difficult to treat reproductive (or other) health problems. It also allows sample collection from the upper genital tract when invasive specimen retrieval is not recommended such as in cases of non- sexually active young women, due to cultural restrictions.
  5. IN ROUTINE GYNECOLOGICAL SCREENING: We propose the integration of menstrual tissue testing in routine gynecological screening examinations together with cervical/vaginal fluid cultures, pap smears and colposcopy when necessary, to ensure accurate and timely treatment of infection from an early age to prevent potentially serious side effects of chronic undetected infections.
  6. IN ELIMINATION OF SEXUALLY TRASMITTED INFECTIONS: The Hidden-C® Test can be applied as a valuable diagnostic tool in preventive medicine to diminish the sexually transmitted infections within a population. As a non-invasive method, The Hidden-C® Test can be successfully applied both in teenagers and sexually active women and is proposed as a preventive strategy for the prevention, control, screening and elimination of sexually transmitted infections.


  • Easy, non-invasive collection of sample: self-collected menstrual blood fluid and shipment to the reference laboratory by post
  • Specimen (menstrual fluid) is representative of the whole endometrium
  • Fast turnaround time of results within 1 to 5 working days
  • High sensitivity (>95%) and specificity (>99%)
  • Safe storage and transport of samples by post for testing
  • Low-cost
  • Detects infertility and endometritis-associated microorganisms: Chlamydia spp, Mycoplasma spp, Ureoplasma spp, other bacteria (eg. Mycobacteria, Atopobium vaginae, Gardnerella vaginalis), viruses and fungi
  • Easy to repeat the procedure for monitoring the antibiotic/antiviral therapy results


  1. Michou IV et al. (2014). Molecular investigation of menstrual tissue for the presence of Chlamydia trachomatis, Ureaplasma urealyticum and Mycoplasma hominis collected by women with a history of infertility. J Obstet Gynaecol Res. Jan;40(1):237-42.
  2. Low N (2004) Current status of chlamydia screening in Europe. Euro Surveill;8.
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  4. Fenton KA, Lowndes CM (2004) Recent trends in the epidemiology of sexually transmitted infections in the European Union. Sex Transm Infect 80:255-263.
  5. Shelagh MR et al. (2015) Genital Chlamydia prevalence in Europe and non-European high income countries: systematic review and meta-analysis. PLoS One 10(1):e0115753.
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  9. Peipart JF (2003) Clinical practice. Genital chlamydial infections. NEJM; 349:2424-30.
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