HCV is an enveloped virus containing a single-stranded positive sense RNA genome of approximately 9,500 nucleotides 1 . On the basis of genetic similarity, HCV has been classified into six major genotypes (1-6) and numerous subtypes 2 . HCV treatment is evolving rapidly.
Since July 1, 2016, two combinations of DAAs (direct acting-antivirals) HARVONI (Gilead sofosbuvir and ledipasvir) and VIEKIRA PAK (ritonavir-boosted paritaprevir/ombitasvir and dasubavir) have been funded in New Zealand. Both have cure rates of 95 per cent, fewer side effects and shorter treatment duration compared to previous treatments. All patients infected with HCV genotype 1, except for those with decompensated cirrhosis can access VIEKIRA PAK. Only patients with decompensated cirrhosis can access HARVONI 3 .
Resistance of HCV to DAAs is related to the nucleotide substitutions emerging during replication. Full resistance depends on the number and type of RASs (Resistance-Associated Substitutions) acquired. The genetic barrier to resistance varies with drug class, specific drug, and HCV genotype or subtype 4 .Most of the 5% of patients who relapse after treatment with HARVONI or VIEKIRA PAK have developed resistance to NS5A inhibitors. Before retreating these HARVONI or VIEKIRA PAK failures, it is important to determine their NS5A resistance profile as this will inform the most appropriate retreatment regimen.
We perform pan-genotyping NS5A sequencing using Sanger Sequencing to determine RAS for patients who have failed virologic treatment. An informative fragment of the NS5A gene is amplified, sequenced and then analysed for drug resistance associated mutations. The analysis is done through DeepChek -HCV (CE-IVD marked, ABL_TherapyEdge SA) diagnostic software , which produce a report with the resistance outcomes. Resistance is analysed according to 3 different algorithms but routinely reported according to the Geno2pheno database. Where discrepancies of analysis exist a comment will be attached to the result, detailing the variation.
A comprehensive PDF report is available on request.
Source: LabPlus Auckland Test Guide
Microbiology - Virology
Dedicated EDTA tubes required, minimum 4mL whole blood
Please refer to separating guide in Additional Information section below
If sample arrives frozen, please ensure it does not thaw.
HCV resistance genotyping
The requirements for test acceptance are:
The request MUST state that the patient has failed a regimen containing an NS5A inhibitor (i.e. either VIEKIRA PAK, HARVONI, ZEPATIER or generic daclatasvir plus sofosbvuvir (please list drugs).
A recent (within past month) HCV viral load result is required.
If HCV viral load and resistance genotyping are ordered on the same request, 2 full EDTA tubes is sufficient.
Resistance testing can be added on to an HCV viral load request if required, samples are stored frozen for 3 months.
If separated sample will arrive within 70 hours of collection, chilled transport is acceptable.
If this timeframe cannot be guaranteed, please send samples frozen.
If HCV viral load and resistance genotyping are ordered on the same request, please send 2 aliquots.
Sanger sequencing, performed at LabPlus Auckland.
Antiviral Drugs included:
Referred to Labplus Auckland
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