Resistance testing in Asia

[Life]

I was wondering if anyone could shed some light on resistance testing and if it is truly necessary.  I have a friend in Hong Kong who just tested positive..  His doctor is reluctant to do this test..  Maybe its a moot issue in that region or it is an extravagance??  I was put thru this test by my doc here in the US....

Here is the conversation and documentation sent by his doctor.......


My Doctor replies is as follows ….

“controversial in Hong Kong because we have not had many resistant strains (unlike US)”

Also, he says that the total cost of Geno / pheno testing is HK$14,400 , which is about US$1,900

He also sent me a pretty confusing document on resistance testing , which I have attached.

This guy is well known, very well known. He mixes it with Gallo and all the big boys from the US, and I am somewhat confused why he seems reluctant to suggest resistance testing. I am guessing its cos there are only 1,800 confirmed HIV cases in HK, and so far they haven’t send many, if any , resistant strains

HIV Resistance Testing sheet hand out....

Resistance in HIV is not an “all or none” phenomenon. It is manifest as a decreased susceptibility or a relative reduction in susceptibility.

Resistance testing is useful for (a) those who have failed treatment (b) those with incomplete viral suppression and (c) possibly for those who have just been diagnosed.

In relation to testing at diagnosis it is noted that the number of naïve patients (ie those who have never been treated) who have genotypic mutations at the time of diagnosis in the USA in 2005 was around 15% with 10% NRTI, 4% PI, 3% NNRTI and 4% showing mutations to 2 classes of drugs. It seems likely that those with acute infection or those who have recently been infected (ie within 1-2 years) are more likely to have resistance than those with chronic infection. On the basis of this the IAS recommend resistance testing at the time of diagnosis whereas the US DHSS recommend ‘consider’ resistance testing at diagnosis in those with chronic infection and do it in acute or recent infections.     

Resistance testing allows us to select the best combination of drugs for treatment.

There are 3 types of resistance in HIV:
•   Clinical resistance: HIV multiplies despite drugs. This is manifest as a high viral load
•   Phenotypic resistance: the virus multiplies in a test tube in the presence of antiviral drugs. Test results are expressed compared to the suppression seen of the sensitive wild virus. Thus a 2-fold resistance indicates growth is increase twofold versus the wild virus.  Resistance is defined according to the drug; thus a 1.6-fold or more result indicates resistance to stavidine whereas a 3.8-fold or more result indicates resistance to tenofovir. The cost is around US$800
•    Genotypic resistance measures genetic mutations in the HIV virus likely to confer resistance. Unfortunately there are many manufacturers of genotypic kits and their definitions of resistance differs. This can lead to significant misinterpretation of results. The cost is around US$250.

Sometimes the results of genotypic and phenotypic tests differ and expert interpretation is needed.  Genotypic and phenotypic testing can only be done at viral loads .500 (preferably >1,000) and results are more accurate in those with higher viral loads. 

Genotypic testing is usually adequate in naïve patients – and we would tend to use phenotypic testing if the mutation pattern in genotypic testing is complex. However the more information the better and if cost is not a factor then do both genotypic and phenotypic testing.

Many drugs in the same class will show cross-resistance on testing eg if someone is resistant to nivirapine they are likely to be resistant to efavirenz.

In those who are on a failing regime HIV virus becomes detectable – whereas previously it was undetectable. This indicates evolving resistance. However many such patients remain clinically stable for many years# and many clinicians keep them on the same regime. However evidence suggests that it is best to change the regime. When changing the regime change all the drugs and resist changing drugs sequentially.

# this is often an expression of “viral finess.” This is the ability of HIV to replicate, infect and kill T-cells. Fitness varies between wild and resistant strains and some resistant strains have decreased viral fitness.
 

[komnaes]

I am in Hongkong and I am concerned about this too - I just have my result back only 5 days ago and still have not scheduled my first big blood test (will do that today, as the nurse in the government wants me to see a psychiatrist first this afternoon).

The question of whether the local clinics will do resistance tests has been on my mind since yesterday and I immediately called a social worker in the Hongkong AIDS Foundation, and he assured me that they do. But I suppose I will find out.

I think one major factor that I am not as freaked out about my status is that the clinics here are probably some of the best in the world, not just Asia. I will find out more though but as of now I am confident that I will be getting the right test/treatments and there will be supports from local NGOs when I need them.