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The Viral Load in Hepatitis
C
Introduction
The first diagnosis of your hepatitis C was probably
made due to the result of an (relatively cheap) antibody test
such as ELISA or similar. The result of this test was ' positive ',
and that means that your body at some time has come into contact
with the hepatitis C virus and that the immune system of your body
developed antibodies against this virus to fight this infection.
In order to find out, whether the virus is still active in your
body, a different test has to be made: The presence of the virus
has to be detected directly.
For this purpose there are two types of tests available,
the qualitative PCR test or a quantitative test.
The qualitative test can have only two results: Either
the virus is detected, or the virus is not detected. If the virus
is detected (result: positive), you know only that you do have the
virus in your body, but you don't know, in which quantity it is in
your body. If no virus is detected (result: negative), you
know that you either don't have the virus (any more), or that its
concentration is so low that it cannot be detected.
The quantitative test on the other hand gives you a
number for the...
(I.) Viral Load
Your viral load is the amount of viruses present in a given
volume of your blood (usually 1 millilitre = 1 cubic
centimeter). More precisely, it means that the amount of hepC
genetic material found in your blood corresponds to as many hep C
viruses as the given number says. Therefore the given number
denotes 'viral equivalents' (abbreviated: eq ).
The viral load can range from 'not detected' to
hundreds of millions hepC viruses per milliliter, or up to near a
hundred million IUs (International Units) per milliliter.
(II) What does"negative", "not detectable" mean?
The meaning of "not detectable" or "negative" depends on the
test used.
The most sensitive test is normally the qualitative PCR
test. In the laboratory, to which I go, the detection limit for
this test is 100 eq/ml. That means that any viral load below
100eq/ml would give the result "negative", and any viral load
above 100eq/ml would give the result "positive" . But, in
this qualitative test, 'positive' can mean everything above the
detection limit, 110eq/ml as well as 11,000,000eq/ml  it
doesn't give you a number for the viral load.
The quantitative HCV RNA test via *PCR* is
often somewhat less sensitive  a detection limit of 200eq/ml
in the case of the laboratory, to which I go. But as the name says:
It measures the quantity of viruses in your blood. It has the
advantage to give you a number for the viral load.  There is also
a cheaper *bDNA* test. But its much less sensitive,
with its detection limit being at approximately 200,000eq/ml.
So, when you are " negative ", maybe there is no hepatitis C
virus in your blood. But maybe also you do have hepatitis C viruses
in your blood, but the number of viruses is lower than the
detection limit of the test.  In clinical trials, ' negative
' nowadays normally is defined as less than 100 Eq/ml.
III.) "Positive"  What's
important to note, besides the pure numbers
When you get back the result of your HCV 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.
A) Volume
The volume of blood that the number refers to is usually one
millilitre (ml). But some labs give the number for 20
microlitres = 1/50 millilitre. So in these cases you have to
multiply the result of the viral load by 50 to get the number for 1
millilitre.
B) 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 I would say is just the plain number of viruses per
millilitre, like 1.5 Million/ml, or 1,500,000/ml.
Thanks to the WHO, we now have another way to express the viral
load, the IU (International Unit).
1.) Viral load given in IU
Giving the viral load in IU probably soon will replace all other
ways to express the viral load  until recently it was expressed
most frequently in eq or Meq. But at the moment and in old
lab reports a wide variety of ways to give the viral load still can
be found.
The IU = International Unit for the hepatitis C viral load is a
unit more or less arbitrarily fixed. Labs now can take part in
international comparison tests using a calibrated sample and
thereby normalize their results to an international standard. So,
in the future results from different laboratories should be
directly comparable.
For converting numbers from eq to IU and vice versa, different
labs use different conversion factors, in the range from 2 to 5
viruses per IU. If you do not know the factor that your lab uses,
using a factor of three might be reasonable. That means: Viral
loads given in eq/ml have to be divided by three to get the viral
load in IU/ml. And, viral loads given in IU/ml have to be
multiplied by three to get the result in eq/ml.
2.) Viral loads given by virus count
a.) 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 Megaequivalents/ml or again 1,730,000 equivalents/ml.
Sometimes also the prefix "k" (kilo) is used, it means
thousands.
the following ways to express the viral load are only rarely
seen today:
b.) 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. Exponential numbers might
show up in a form like 1.73x10^{6} or 1.73x10(exp)6 or
1.73x10^6 which are all the same number 1,730,000.
c.) Logarithmic 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. So, if this logarithmic number is given to
you, you need a calculator to convert this to a plain number.
You have to use the function 10^{x}, where you have to
replace x with the logarithmic number, in the above case
6.24. You have to calculate 10^{6.24} = 1,730,000 ,
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 (to
the 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 ( but I have never seen that ) 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 !
3.) Viral load given by weight
Sometimes, the lab reports the amount of genetic material found
by its weight. 1 pg (picogram) 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.
Therefore it is important to have a close look at your lab
report and see in what units the result is given !
And now, of course, you would like to
know whether your viral load is low or high....
Although there is no general consensus on the definition of
'low' and 'high' with respect to the viral load, data from the Web
pages of the National Genetics
Institute give you an idea: As can be seen there, the average
viral load is at 3.2 Million eq/ml.  So, to make a simple scheme I
would propose the following classification:
Viral Load in eq/ml

Classification

Remarks

below 200.000

very low

below detection limit of bDNA test

200,0001,000,000

low


1,000,0005,000,000

medium

average viral load at 3,200,000 eq/ml

5,000,00025,000,000

high


above 25,000,000

very high


Expressed in IU, the average viral load is at 1 Million IU/ml.
All these classifications of viral load of course make sense only
for patients that are not being treated against HCV.
Please note: I am no MD. I am just an
informed layperson. What I have learned and written down here
cannot and should not replace the advice from a good hepatologist!
And I have written this in English, which is a foreign language for
me. So beware....
©
Albrecht.Ernst
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