Medical Articles

Title: HPV-PCR
Date: 07-Oct-2012

Introduction
The most important aspect for any patient test is exact diagnosis. The new innovative HPV PCR test being offered to patients by Gribbles Pathology is now the most informative and affordable HPV-PCR test available.

With HPV being one of the most common sexually transmitted infections, combined with the reluctance of women to have regular screenings, the ability to identify and type the exact HPV present whether it is a "high" or "low" risk type allows you to significantly improve patient management and alleviate your patient's anxiety when an abnormality is detected.

The uniqueness of the Gribbles test when compared with other HPV tests, Liquid Based Cytology (LBC) or regular Pap tests available is its ability to report exactly which "high" risk HPV genotype was detected, even if there is more than one.

Patients who have a high-risk HPV result should be referred for gynaecological assessment.


Low Risk and High Risk HPV Types
Low risk HPV types, most commonly HPV 6 and 11, are associated with benign genital warts and benign cervical lesions, with no significant oncogenic potential. On the other hand, high risk HPV types, notably HPV 16, 18, 31 and 45 have the potential to cause high grade cervical intraepithelial neoplasia (ON) and cervical carcinoma.


Human Papillomavirus Infection and Cervical Cancer
Studies show that more than 95% of all cervical cancers are associated with human papillomavirus (HPV) infection. There are about 40 known sexually transmitted HPV types, of which 13 (HPV types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 68) have been established as having oncogenic (high risk) potential. Of these, HPV type 16 alone causes more than 50% of cervical cancers and HPV 18 causes 10% to 15%, followed by HPV 45 (around 7%) and HPV 31 (approx 3%). The ability to detect individual types of HPV viruses in cervical cytology specimens, is, therefore, of considerable clinical value.


HPV Test using PCR Technology
The Molecular Biology Department at Gribbles Pathology in conjunction with Genera Biosystems has jointly developed a sensitive molecular test for the presence of HPV that also allows identification of any individual high risk genotypes. The assay uses the polymerase chain reaction (PCR) and a specific probe labelled silica bead hybridisation technique which enables the presence of one of more of the 13 oncogenic genotypes as well as other (so called low risk) types to be detected. The assay being PCR based is more sensitive than a hybrid capture assay which does not have an amplification step. It also has internal controls that allows confirmation of adequate material in the sample, and detection of any substances inhibitory to the PCR step. These are both very important in preventing potential false negative results. The assay has been validated to National Pathology Accreditation Advisory Council (NPAAC) standards and requires either a liquid-based cervical cytology sample (ThinPrep) or a plain (dry) cervical swab. The assay will determine and report the genotype of the HPV detected. For example, if a high-risk genotype is detected, the molecular biology report may be as follows:
 

Human Papillomavirus
(High Risk Genotypes)    
Detected
Genotypes Identified 16, 18


The assay will also detect other (low risk) types of HPV, if present. The presence of low risk HPV will be reported, but not genotyped.

The advantage of this PCR based assay, unlike the other currently available assays, is that it is able to report the actual genotype of the HPV detected, rather than simply issue a broad statement such as "high risk type detected".


Clinical Applications of HPV Testing
The presence of an infection with a high risk HPV type would serve to triage women needing close cervical smear and/or colposcopic follow up, particularly in the following circumstances:

  1. Patients with equivocal cytology and/or histology results such as minor squamous abnormalities, non specific squamous changes and equivocal HPV infection/CIN I.
  2. Patients with low grade abnormalities, such as HPV infection and/or CIN I, reported on cytology and/or histology.
  3. Patients with high grade CIN reported on cervical smears, who turn out to have normal findings or low grade abnormalities on colposcopy and/or histology.
  4. Post treatment follow up of patients with high grade CIN.

HPV testing can be performed alone, or as an adjunct to the routine Pap smear, either by direct request, or by "reflex testing" of a liquid-based sample. "Reflex testing" is where the requesting doctor wishes HPV testing to subsequently proceed on the basis of abnormal cytology findings on a current liquid based sample.

At this stage the assay is not being offered for genotype reporting on types 6 and 11 that are commonly associated with genital/venereal warts nor for testing on males or noncervical samples.


Gribbles HPV-PCR Compared to Other Tests

  Gribbles
HPV-PCR
Hybrid capture Liquid Based Cytology (LBC) Pap smear
Detects generic HPV Yes Yes Yes Yes
Detects "high-risk" HPV types Yes Yes N/A N/A
Detects "low-risk" HPV types Yes Yes N/A N/A
Identifies specific HPV genotype Yes No No No
Has internal control to reduce false negatives Yes No N/A N/A
Cost effective to patient Yes No Yes Yes


In Summary: HPV-PCR

  • Able to identify specific high-risk HPV genotypes.
  • HPV-PCR test is more sensitive than current screening methods.
  • Potential to reduce false negative results.
  • The test has been validated to National Pathology Accreditation Advisory Council (NPAAC) standards.

 

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