AMPLICOR HIV1 MONITOR™ Slide Rule
The Slide Rule has been developed by Roche Diagnostics to be used in conjunction with the AMPLICOR HIV1 MONITOR™ viral load test. It is helpful for doctors and people with HIV to keep track of viral load levels and is a useful tool in converting RNA copies/mL results into logarithm (log) values.
The Slide Rule also calculates the log change, or log_{10} variation from a new viral load measurement and a previous test result. This enables an assessment of the progression of the HIV virus and the effects that antiHIV therapy may be having.
Using the Slide Rule is both quick and easy.
To determine log differences in viral load levels:

Type in the test results for the two tests to be compared ie. latest and previous viral loads. The figures should be in HIVRNA copies/mL plasma (you will need to make sure that the numbers are typed in without commas, ie. 5000 not 5,000).

Press Calculate. The log value for each test will be shown underneath each measurement, followed by the log variation and fold variation.

Press Reset if you want to do another calculation.

How to use AMPLICOR HIV1 MONITOR™ Slide Rule
Log values
Log value is the measurement used by clinicians to describe viral load in an infected individual and expresses the viral load values as a power of ten. The scale is used because the magnitude of changes can only be captured on graphs or diagrams by using a log scale  turning huge numbers (copies/mL) into ‘manageable’ figures.
The log is not an absolute number in itself, but expresses numbers to the power of ten.
The table below demonstrates the relationship between RNA copies / mL and equivalent log values.
HIVRNA Level

Log_{10}

copies/mL

Log_{10}

copies/mL

7

10,000,000

3.5

3,162

6.9

7,943,282

3.4

2,512

6.8

6,309,573

3.3

1,995

6.7

5,011,872

3.2

1,585

6.6

3,981,072

3.1

1,259

6.5

3,162,278

3

1,000

6.4

2,511,886

2.9

794

6.3

1,995,262

2.8

631

6.2

1,584,893

2.7

501

6.1

1,258,925

2.6

398

6

1,000,000

2.5

316

5.9

794,328

2.4

251

5.8

630,957

2.3

200

5.7

501,187

2.2

158

5.6

398,107

2.1

126

5.5

316,228

2

100

5.4

251,189

1.9

79

5.3

199,526

1.8

63

5.2

158,489

1.7

50

5.1

125,893

1.6

40

5

100,000

1.5

32

4.9

79,433

1.4

25

4.8

63,096

1.3

20

4.7

50,119

1.2

16

4.6

39,811

1.1

13

4.5

31,623

1

10

4.4

25,119

0.9

8

4.3

19,953

0.8

6

4.2

15,849

0.7

5

4.1

12,589

0.6

4

4

10,000

0.5

3

3.9

7,943

0.4

3

3.8

6,310

0.3

2

3.7

5,012

0.2

2

3.6

3,981

0.1

1

Log Variation
Log variation is a way to measure the viral load change over time.
Log variation = first log result  the second log result.
Fold variation
Fold variation is another method of measuring the change in viral load between two test results. The fold variation is obtained by dividing the larger viral load (copies/mL) by the smaller viral load (copies/mL). For example, if the first test has a baseline of 1000 copies/mL and the second test is 500 copies/mL the fold variation would be 2.
The table below demonstrates the relationship between viral load log variation and fold values variation.
Conversion Table

Log_{10} Variation

Fold Variation

0.18

1.5

0.30

2.0

0.48

3.0

0.60

4.0

0.70

5.0

0.78

6.0

0.85

7.0

0.90

8.0

0.95

9.0

1.00

10.0

2.00

100.0

3.00

1,000.0

On April 24, 1998, the CDC published the "Report of the NIH Panel to Define Principles of Therapy of HIV Infection and Guidelines for the Use of Antiretroviral Agents in HIVInfected Adults and Adolescents", which stated that differences greater than 0.5 log_{10} copies on repeated measures of plasma HIV RNA likely reflect biologically and clinically relevant changes.
