Human papillomavirus (HPV) is a group of over 200 related viruses that commonly infect skin and mucous membranes. HPV genotyping is a laboratory method used to identify the specific type or strain of HPV in a sample. This process pinpoints which particular HPV type is causing an infection, which is beneficial because different HPV types have varying health implications.
Understanding HPV Types
HPV is a diverse family of viruses, categorized into two main groups based on their disease potential: low-risk and high-risk. Low-risk HPV types typically cause warts, such as genital warts, which are usually benign. For instance, HPV types 6 and 11 are responsible for about 90% of genital warts cases.
High-risk HPV types are linked to various cancers, including cervical, anal, oropharyngeal, vaginal, vulvar, and penile cancers. Approximately 14 high-risk HPV types exist, with HPV 16 and 18 being the most common, accounting for 70-80% of cervical cancers globally. Other high-risk types, such as HPV 31, 33, and 45, can also contribute to cervical abnormalities and cancers. Identifying these types is important because persistent infection with high-risk HPV is necessary for developing cervical precancerous lesions and invasive carcinoma.
The Purpose of HPV Genotyping
HPV genotyping is used in clinical management, especially for cervical cancer screening and follow-up. By identifying specific HPV types, it helps assess an individual’s likelihood of developing high-grade cervical lesions or cancer. For instance, detecting HPV 16 or 18, which have the highest cancer potential, may prompt immediate follow-up actions like a colposcopy and biopsy.
Genotyping also guides clinical decisions after abnormal Pap test results. Knowing the specific HPV genotype helps determine if more frequent monitoring or intervention is needed. This is relevant for differentiating between a new, transient infection and a persistent infection with a high-risk type, as persistent infections pose a greater risk for disease progression. For example, HPV 16 shows a higher likelihood of persistence and progression to Cervical Intraepithelial Neoplasia grade 3 (CIN3) and invasive carcinoma compared to other high-risk HPV types.
How HPV Genotyping is Performed
HPV genotyping begins with sample collection, similar to a Pap test. For cervical cancer screening, a healthcare provider collects cells from the cervix using a swab or small brush. These collected cells are then sent to a specialized laboratory for analysis.
In the laboratory, the genetic material (DNA) from the collected cells is extracted. This HPV DNA then undergoes amplification, often using Polymerase Chain Reaction (PCR). PCR creates many copies of the HPV DNA, making it easier to detect and identify.
After amplification, various laboratory techniques pinpoint the specific HPV genotypes present. These include hybridization-based methods, which use probes that bind to specific HPV DNA sequences, or DNA sequencing, which determines the virus’s exact genetic code. The results indicate which high-risk HPV types were detected, or if no HPV was found, such as “Positive for HPV 16” or “Negative for all tested HPV types.”