Viral load is the amount of virus present in the bloodstream. It is expressed as the amount of viral genetic material (RNA) per milliliter of blood. Viral load is not related to the amount of liver damage, or to how sick someone is.
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Types of HCV Viral Load Tests
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There are two categories of HCV viral load tests:
Qualitative viral load tests — These tests determine the presence of HCV RNA in the blood. This type of test is usually used to confirm chronic infection with HCV. If viral RNA is detected, a positive result is reported; if viral RNA is not detected, the test result is negative.
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Quantitative viral load tests — These tests measure the amount of virus in one milliliter of blood. They are often used to assess whether or not treatment with interferon or interferon plus ribavirin is likely to be successful and, later, if treatment is working.
.
Types of HCV Viral Load Tests
.
There are two categories of HCV viral load tests:
Qualitative viral load tests — These tests determine the presence of HCV RNA in the blood. This type of test is usually used to confirm chronic infection with HCV. If viral RNA is detected, a positive result is reported; if viral RNA is not detected, the test result is negative.
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Quantitative viral load tests — These tests measure the amount of virus in one milliliter of blood. They are often used to assess whether or not treatment with interferon or interferon plus ribavirin is likely to be successful and, later, if treatment is working.
Source
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When you get back the result of your Hepatitis C RNA quantitative test, and when the lab was able to determine the amount of virus in your blood, then it is important to write down not only the number, but also in what units this number is given.
.
.
When you get back the result of your Hepatitis C RNA quantitative test, and when the lab was able to determine the amount of virus in your blood, then it is important to write down not only the number, but also in what units this number is given.
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I) Volume
The volume of blood, that the number refers to, is usually one milliliter.
But some labs give the number for 20 microliters = 1/50 milliliter. So in these cases you have to multiply the result of the viral load by 50 to get the number for 1 milliliter.
II) Amount of Virus
Unfortunately, there are several ways to express the viral load. So, in order to be able to compare different results, you have to know how to convert these numbers to some standard format, which let’s say is just the plain number of viruses per milliliter, like 1.5 Million/ml, or 1,500,000/ml. (both of these numbers are the same).
a) Measure by weight
Sometimes, the lab reports the amount of genetic material found by its weight. 1 pg (pico-gram) of genetic material corresponds to about 1 million virus equivalents, so, if your lab result is given in picograms, just multiply the lab result by 1,000,000, and you have the number of viruses.
b) Measure by virus count
i) Plain numbers
Often the virus count is expressed as a plain number, like 1.73 million, or 1,730,000 or 1730000. Millions sometime are abbreviated by the prefix “M” (Mega). So when you see 1.73 Meq/ml, it means 1.73 Mega-equivalents/ml or again 1730000 equivalents/ml..
ii) Exponential format
Large numbers are often expressed in exponential form, that means a number, multiplied by 10 with an exponent. To convert this to normal numbers, append as many zeroes to a “1″ as the exponent says, and multiply this with the number. In some lab report, the viral load was “Hep C RNA Quant 17.3 x 10(exp) 5 equivalents/ml”. So, with 5 as exponent, you have to append 5 zeroes to a “1″, that gives 100000, and multiply this with the number 17.3, that gives 1730000 as the viral load. Normally this would be written 1.73×10(exp)6, or 1.73×106 , (which are again the same number).
17.3×105 = 1.73×106 = 1,730,000
iii) Logarthmic format
Now, recently some people express these numbers also in logarithmic form (logarithmic transformed number).
log(1730000)=6.24
6.24 is the logarithmic transformed number of the viral load of our above example. A result of 3.5 for a viral load, that someone reported, seems to be such a number (unless he forgot to write down a “10″ and an exponent). You need a calculator to convert this. You have to use the function 10x , where you have to replace x with the logarithmic number, in the above case 3.5. The result would be: 103.5 = 3162 virus equivalents per milliliter.
When you take the logarithmic number from the first example, 6.24, you have to calculate 106.24 = 1730000 , and here we have the original number of virus equivalents again. If you don’t have a calculator, you can estimate the order of magnitude of a viral load expressed as a logarithmic number. From the logarithmic number, you take the first digit (left of the point) and add 1 to this number. This gives you the number of digits that your viral load has (expressed as a plain number).
Example: Logarithmic number 6.24
Left of the point is “6″. 6+1 = 7
The number that gives the viral load is 7 digits long, that means it is between 1,000,000 and 9,999,999 (digit # 1 234 567)
The next digit (right of the point of the logarithmic number) shows whether you are high or low in the range.
In case you have a logarithmic number *and* a blood volume other than 1 ml, you have to convert the logarithmic number to a plain number *first*, and then correct it to correspond to 1 ml !
Therefore it is important to have a close look at your lab report and see in what units the result is given!
There is still no general agreement on what Viral Load is considered low and what is high in Hepatitis C. This interpretation makes sense for people not currently being treated – for someone who is 6 months into an INF + RIBA trial, even 200,000 could be considered a high titer.
(Numbers are Virus Equivalents per Milliliter)
below 200,000 very low (undetectable by *bDNA* test)
200,000 to 1,000,000 low
1,000,000 to 5,000,000 medium
5,000,000 to 25,000,000 high
above 25,000,000 very high
Once again, please note that this information is not written by an MD or medical expert. Nothing can (or should) take the place of appropriate medical care.
The volume of blood, that the number refers to, is usually one milliliter.
But some labs give the number for 20 microliters = 1/50 milliliter. So in these cases you have to multiply the result of the viral load by 50 to get the number for 1 milliliter.
II) Amount of Virus
Unfortunately, there are several ways to express the viral load. So, in order to be able to compare different results, you have to know how to convert these numbers to some standard format, which let’s say is just the plain number of viruses per milliliter, like 1.5 Million/ml, or 1,500,000/ml. (both of these numbers are the same).
a) Measure by weight
Sometimes, the lab reports the amount of genetic material found by its weight. 1 pg (pico-gram) of genetic material corresponds to about 1 million virus equivalents, so, if your lab result is given in picograms, just multiply the lab result by 1,000,000, and you have the number of viruses.
b) Measure by virus count
i) Plain numbers
Often the virus count is expressed as a plain number, like 1.73 million, or 1,730,000 or 1730000. Millions sometime are abbreviated by the prefix “M” (Mega). So when you see 1.73 Meq/ml, it means 1.73 Mega-equivalents/ml or again 1730000 equivalents/ml..
ii) Exponential format
Large numbers are often expressed in exponential form, that means a number, multiplied by 10 with an exponent. To convert this to normal numbers, append as many zeroes to a “1″ as the exponent says, and multiply this with the number. In some lab report, the viral load was “Hep C RNA Quant 17.3 x 10(exp) 5 equivalents/ml”. So, with 5 as exponent, you have to append 5 zeroes to a “1″, that gives 100000, and multiply this with the number 17.3, that gives 1730000 as the viral load. Normally this would be written 1.73×10(exp)6, or 1.73×106 , (which are again the same number).
17.3×105 = 1.73×106 = 1,730,000
iii) Logarthmic format
Now, recently some people express these numbers also in logarithmic form (logarithmic transformed number).
log(1730000)=6.24
6.24 is the logarithmic transformed number of the viral load of our above example. A result of 3.5 for a viral load, that someone reported, seems to be such a number (unless he forgot to write down a “10″ and an exponent). You need a calculator to convert this. You have to use the function 10x , where you have to replace x with the logarithmic number, in the above case 3.5. The result would be: 103.5 = 3162 virus equivalents per milliliter.
When you take the logarithmic number from the first example, 6.24, you have to calculate 106.24 = 1730000 , and here we have the original number of virus equivalents again. If you don’t have a calculator, you can estimate the order of magnitude of a viral load expressed as a logarithmic number. From the logarithmic number, you take the first digit (left of the point) and add 1 to this number. This gives you the number of digits that your viral load has (expressed as a plain number).
Example: Logarithmic number 6.24
Left of the point is “6″. 6+1 = 7
The number that gives the viral load is 7 digits long, that means it is between 1,000,000 and 9,999,999 (digit # 1 234 567)
The next digit (right of the point of the logarithmic number) shows whether you are high or low in the range.
In case you have a logarithmic number *and* a blood volume other than 1 ml, you have to convert the logarithmic number to a plain number *first*, and then correct it to correspond to 1 ml !
Therefore it is important to have a close look at your lab report and see in what units the result is given!
There is still no general agreement on what Viral Load is considered low and what is high in Hepatitis C. This interpretation makes sense for people not currently being treated – for someone who is 6 months into an INF + RIBA trial, even 200,000 could be considered a high titer.
(Numbers are Virus Equivalents per Milliliter)
below 200,000 very low (undetectable by *bDNA* test)
200,000 to 1,000,000 low
1,000,000 to 5,000,000 medium
5,000,000 to 25,000,000 high
above 25,000,000 very high
Once again, please note that this information is not written by an MD or medical expert. Nothing can (or should) take the place of appropriate medical care.
Posted at Avail Clinical On February 4th, 2011
http://www.availclinical.com/tag/hepatitis-c-treatment/
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http://www.availclinical.com/tag/hepatitis-c-treatment/
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HCV Viral Load Tests
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Alan Franciscus, Editor-in-Chief
Liz Highleyman
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Viral load tests are blood tests that measure HCV ribonucleic acid (RNA, or genetic material) in the blood. The presence of viral RNA indicates that the virus is actively replicating (reproducing and infecting new cells). A viral load test is usually first done after a person has tested positive for exposure to HCV based on an antibody test. A blood sample is taken and the amount of HCV RNA in a milliliter of blood is measured. Viral load tests confirm whether an individual is actively infected with HCV. Viral load test results were previously measured in number of copies, but are now typically reported in terms of International Units per milliliter (IU/mL).
Types of HCV Viral Load Tests
There are two categories of HCV viral load tests:
Qualitative viral load tests — These tests determine the presence of HCV RNA in the blood. This type of test is usually used to confirm chronic infection with HCV. If viral RNA is detected, a positive result is reported; if viral RNA is not detected, the test result is negative.
Quantitative viral load tests — These tests measure the amount of virus in one milliliter of blood. They are often used to assess whether or not treatment with interferon or interferon plus ribavirin is likely to be successful and, later, if treatment is working.
There are currently three tests commonly used for HCV viral load testing:
Polymerase chain reaction (PCR) — PCR tests detect HCV RNA in the blood, which indicates current active infection. This type of quantitative PCR test is very sensitive, and can measure as few as 50 IU/mL.
Branched-chain DNA (bDNA) — The bDNA method quantitative viral load testing is easier (and cheaper) to use for a large number of samples, but only measures viral loads greater than 500 IU/mL. This means that if a person has a viral load below 500 IU/mL, HCV could be present in the blood but not detected by the test.
Transcription-mediated amplification (TMA) — TMA technology allows for the amplification and detection of nucleic acids (components of genetic material) in the blood. This test can measure as few as 5-10 IU/mL. This newer test appears easier and cheaper to use, streamlining test processing and producing consistent, reliable, and more rapid results.
Interpreting Viral Load Test Results
HCV viral load is often reported as low or high.
Expressed as copies/mL:
·Low: less than 2 million copies
·High: more than 2 million copies
Expressed as International Units (IU/mL):
·Low:less than 800,000 IU/mL
·High:more than 800,000 IU/mL
If no HCV RNA is found by a test, a person’s viral load is said to be undetectable. Note that whether viral load is undetectable depends on which test is used. PCR and TMA tests can measure viral loads much lower than those a bDNA test can detect. Importantly, the blood of an individual with a very low viral load may still contain HCV even though the current tests cannot measure it; that is, the virus may not have been truly eradicated from the body.
Viral load test results can vary depending on how a blood sample is handled and stored. Furthermore, results may vary from lab to lab. For this reason, most experts recommend that people should get their viral load testing done by the same laboratory each time, so that results are more comparable.
Changes in viral load are sometimes expressed in terms of logs. A log change is a 10-fold increase or decrease. For example, a change from 1,000,000 IU/mL to 10,000 IU/mL is a 2-log decrease.
Converting copies per milliliter to Inter-national Units
There is no standard conversion formula for converting the amount of HCV RNA reported in copies per milliliter to the amount reported in International Units. The conversion factor ranges from about one to about five HCV RNA copies per IU. Usually the lab report will list the conversion from IU/mL to copies/mL.
Alan Franciscus, Editor-in-Chief
Liz Highleyman
.
Viral load tests are blood tests that measure HCV ribonucleic acid (RNA, or genetic material) in the blood. The presence of viral RNA indicates that the virus is actively replicating (reproducing and infecting new cells). A viral load test is usually first done after a person has tested positive for exposure to HCV based on an antibody test. A blood sample is taken and the amount of HCV RNA in a milliliter of blood is measured. Viral load tests confirm whether an individual is actively infected with HCV. Viral load test results were previously measured in number of copies, but are now typically reported in terms of International Units per milliliter (IU/mL).
Types of HCV Viral Load Tests
There are two categories of HCV viral load tests:
Qualitative viral load tests — These tests determine the presence of HCV RNA in the blood. This type of test is usually used to confirm chronic infection with HCV. If viral RNA is detected, a positive result is reported; if viral RNA is not detected, the test result is negative.
Quantitative viral load tests — These tests measure the amount of virus in one milliliter of blood. They are often used to assess whether or not treatment with interferon or interferon plus ribavirin is likely to be successful and, later, if treatment is working.
There are currently three tests commonly used for HCV viral load testing:
Polymerase chain reaction (PCR) — PCR tests detect HCV RNA in the blood, which indicates current active infection. This type of quantitative PCR test is very sensitive, and can measure as few as 50 IU/mL.
Branched-chain DNA (bDNA) — The bDNA method quantitative viral load testing is easier (and cheaper) to use for a large number of samples, but only measures viral loads greater than 500 IU/mL. This means that if a person has a viral load below 500 IU/mL, HCV could be present in the blood but not detected by the test.
Transcription-mediated amplification (TMA) — TMA technology allows for the amplification and detection of nucleic acids (components of genetic material) in the blood. This test can measure as few as 5-10 IU/mL. This newer test appears easier and cheaper to use, streamlining test processing and producing consistent, reliable, and more rapid results.
Interpreting Viral Load Test Results
HCV viral load is often reported as low or high.
Expressed as copies/mL:
·Low: less than 2 million copies
·High: more than 2 million copies
Expressed as International Units (IU/mL):
·Low:less than 800,000 IU/mL
·High:more than 800,000 IU/mL
If no HCV RNA is found by a test, a person’s viral load is said to be undetectable. Note that whether viral load is undetectable depends on which test is used. PCR and TMA tests can measure viral loads much lower than those a bDNA test can detect. Importantly, the blood of an individual with a very low viral load may still contain HCV even though the current tests cannot measure it; that is, the virus may not have been truly eradicated from the body.
Viral load test results can vary depending on how a blood sample is handled and stored. Furthermore, results may vary from lab to lab. For this reason, most experts recommend that people should get their viral load testing done by the same laboratory each time, so that results are more comparable.
Changes in viral load are sometimes expressed in terms of logs. A log change is a 10-fold increase or decrease. For example, a change from 1,000,000 IU/mL to 10,000 IU/mL is a 2-log decrease.
Converting copies per milliliter to Inter-national Units
There is no standard conversion formula for converting the amount of HCV RNA reported in copies per milliliter to the amount reported in International Units. The conversion factor ranges from about one to about five HCV RNA copies per IU. Usually the lab report will list the conversion from IU/mL to copies/mL.
See Table 1 for a conversion of common viral load tests from IUs to copies.
Table 1: Conversion Chart
Assay Conversion Factor Amplicor HCV Monitor v2.0
(manual procedure) 1 IU/mL = 0.9 copies/ml Cobas Amplicor HCV Monitor v2.0
(semi-automated procedure) 1 IU/mL = 2.7 copies/ml Versant HCV RNA 3.0 Quantitative Assay 1 IU/mL = 5.2 copies/ml LCx HCV RNA Quantitatiive Assay 1 IU/mL = 3.8 copies/ml SuperQuant 1 IU/mL = 3.4 copies/ml
Uses of Viral Load Test Results
Viral load test results have many uses, such as confirming active HCV infection, and predicting and measuring HCV treatment response before, during, and after therapy. Higher HCV viral loads may be associated with a greater risk of HCV transmission, particularly transmission from mothers to infants during pregnancy or birth. Viral load has not been correlated with the risk of sexual transmission. Furthermore, a correlation between HCV viral load and disease progression has not been shown.
Confirming active HCV infection — After a person has tested positive for HCV antibodies, an HCV viral load test is usually performed to confirm active HCV infection. This test is necessary because in up to 25% of people exposed to HCV, the virus can be cleared on its own.
Before treatment — Viral load measurement can help predict how well HCV treatment will work.
The lower the pre-treatment viral load, the more likely it is that a person will respond to current HCV therapies.
During treatment — A decrease in viral load while on therapy indicates that treatment is working. A treatment is said to produce a complete virological response if it reduces viral load to an undetectable level. After 12 weeks of antiviral treatment, a 2-log drop in viral load or elimination of detectable HCV is an indication that the medications are working. If a person does not achieve a 2-log drop in viral load or elimination of detectable HCV after 12 weeks, it is unlikely that he or she will be able to eradicate HCV from his or her body. Viral load tests during treatment can also detect viral breakthrough, or increases in viral load that occur after a previous undetectable test result.
After treatment — Viral load measurements can be used after cessation of therapy to monitor for relapse—that is, to see if the virus becomes detectable again after being undetectable when treatment was completed.
http://www.hcvadvocate.org/news/newsLetter/advocate1003.html#4
Have you heard of rolling circle replication that relates to classic PCR? Definitely an interesting process. A circular plasmid is nicked by an initiator protein and the 3′ end serves as a primer for unnicked strand replication. Replication proceeds around the remaining circular strand producing linear concatemers thereby amplifying the original signal many-fold. Take a look http://cbt20.wordpress.com/2011/03/06/pcr-amplification-circu/
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