by: Albrecht Ernst
Your viral load is the amount of specific viruses that you
have, in a given volume of your blood (usually 1 milliliter
= 1 cubic centimeter). More precisely, it means that the amount
of Hep C 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".
There appears to be no significant correlation between HCV
RNA levels and ALT values or histological activity in patients
untreated by antiviral therapies (Interferon). Viral load
varies between infected individuals but is not a useful prognostic
indicator nor does it measure the severity of virusinduced
liver disease.
WHAT DOES NEGATIVE OR "NOT
DETECTED" MEAN?
The viral load can range from "not detected" to
hundreds of millions. The meaning of "not detected"
or "negative" differs, depending on the test used.
In one lab, the detection limit for the *quantitative* HCV
RNA test by *PCR* is 200 virus equivalents/ml (and with the
*qualitative* test they can detect down to 10 virus equivalents/ml).
The less expensive quantitative *bDNA* test has a detection
limit of about 200,000 virus equivalents/ml. So it is less
sensitive, but above its detection limit it is more accurate
than the PCR test.
So, when you are "negative", maybe you have no
hepatitis C virus in your blood. But maybe also, you do have
hepatitis C virus in your blood, but the number of viruses
is lower than the detection limit. {Example: If the less expensive
quantitative *bDNA* has been used, and the detection limit
is 200,000 virus equivalents/ml, any number less than this
would register as "negative" or "not detected",
when in fact, the viral load could be present, but less than
this detection limit.} Your lab can tell you which testing
measure is used, and your doctor can explain what it means
in your case.
WHAT DOES "POSITIVE"
MEAN?
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.
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 (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.
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 Megaequivalents/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
1.73x10(exp)6, or 1.73x106 , (which are again the same number).
17.3x105 = 1.73x106 = 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.
Source
