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What Is HBV DNA and How Is It Measured?

by Christine Kukka

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HBV DNA carries the genetic blueprint of the virus. How many HBV DNA “particles” or “copies” are found in your blood indicates how rapidly the virus is reproducing in your liver.

To measure your HBV DNA level or “viral load,” clinicians will take a blood sample and send it to a laboratory. The lab measures how many HBV DNA copies are found in a milliliter (about one drop) of blood.

High levels of HBV-DNA, ranging from 100,000 to more than 1 billion viral copies per milliliter, indicate a high rate of HBV replication in your liver. Low or undetectable levels, about 300 copies per milliliter or less, indicate an “inactive” infection.

The World Health Organization established the international unit (IU) or copies per milliliter (mL), written as IU/mL or copies/mL, to measure HBV DNA. But not all labs use this standard. If your lab doesn’t use that measurement, it should be able to convert your results into copies/mL or IU/mL.

The National Institutes of Health have suggested that viral loads that exceed 100,000 copies/mL are “clinically significant.” When people, especially children, are in the “immune tolerant” stage, their HBV DNA levels can reach billions of copies/mL because their immune systems haven’t noticed the infection, or created antibodies to fight the infection.

HBV DNA levels can fluctuate, an HBV DNA test captures your viral load only at the time the test is taken. While researchers know high viral loads are not healthy, they don’t know the specific HBV DNA level at which liver damage occurs.

Keeping track of your HBV DNA levels is a great way to monitor your infection, or to notice if an antiviral medication has stopped working.

How HBV DNA Is Reported
Because there are so many HBV DNA copies in a drop of blood, your lab uses a math equation to report viral load. Instead of writing 100,000 copies/mL, labs may report it as one to the fifth power or 105 or 5 log. In mathematical jargon, a “log” equals a number multiplied by 10. If you  have a viral load of 105 copies/mL, it is actually, 10 X 10 X 10 X 10 X 10 or 100,000.

 A lab report that indicates HBV DNA levels greater than 100,000 copies/mL may be written HBV DNA > 5 log copies/mL or 105 copies/mL.

Every log rise or fall is equivalent to a ten-fold increase or decrease. Doctors monitor HBV DNA levels carefully. A one- or two-log decrease in viral load means an antiviral is working. A one- or two-log increase means an antiviral has stopped working and that viral resistance has developed.

• An undetectable viral load (which means fewer HBV DNA than a lab’s equipment can identify) generally is lower than about 300 copies/mL.

• Moderate levels of HBV DNA begin at about 10,000 copies/mL.

• High levels of HBV DNA can exceed 100,000 copies/mL. It is not unusual for someone with the hepatitis B “e” antigen (HBeAg), or young children, to have millions of HBV DNA.

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