Percentage Loss of Hearing (PLH)

The starting point for the PLH calculation is the baseline audiogram. The baseline audiogram is used as the reference for all other audiograms. Entry, Pre-placement / Pre-employment, Screening / Periodic, Exit and Diagnostic audiograms are all compared to the baseline audiogram’s PLH to obtain the PLHS^{5}. Once the PLH and PLHS has been calculated interpretation of the audiogram can be done and interventions based on the outcome implemented whether this is counselling, claiming for compensation, and / or determining fitness for duty^{5,4,8}. Where there is no valid baseline, the calculation for PLH is applied, a person with normal hearing loss should not have a PLH < 1.1. However, some employers ignored the requirement to perform baseline audiograms within the correct time frames or did not ensure that “baselines” met the criteria and therefore inadvertently missed deadlines for baselines. The office of the Compensation Commissioner made a decision that in such cases where baselines were not performed or did not meet validation criteria within specified deadlines, the baseline PLH shall be considered as 0%^{9,8,4}.

Remember |

If there is no PLHS (PLHS = 0%) from the baseline audiogram after 3 years of annual follow-ups, then the employer can reduce the frequency of testing to every 2 years. However, should a change be visible in the PLH then the surveillance frequency changes back to every 6 months until the PLH has been stabilized. Once the PLH is stable, surveillance testing can continue on an annual basis^{10,6,9}. |

Instruction 171 provides the tables used to calculate the PLH. By using the Hearing Threshold Levels (HTL) determined in each ear, the contribution to the percentage loss of hearing in the frequencies 500, 1000, 2000, 3000 and 4000Hz respectively are calculated, then the sum of the contributions will determine the PLH for the test^{10}.

How to calculate the PLH^{10}

Identify the better and worst result from the audiometry done on the worker

Plot the result for the worst ear down the left side of the table

Plot the result for the better ear across the top of the table

Where the 2 results meet is a figure, write this number down under the frequency on the audiogram / or on a piece of paper

Do this for all the frequencies mentioned above using the table applicable for the frequency tested

Once all the frequencies have been calculated add the results together

The total is the PLH

Example of PLH calculation:

Using the audiogram done today 14/09/2018 and listed numerically in the table 10.1^{10} below:

**Per frequency**work out which is the better and worst ear in the result.- Place a circle around the
per frequency.__worst result__

*Table 10.1: Numerical result of an audiogram*

3. In the example below the **left ear** is worse on the 2000, 4000 and 8000Hz (frequencies) and worse in the right ear is at the 500 and 3000Hz (frequency). All the others are the same in left and right ears.

4. Using the ** 500Hz frequency** and the table for the “

5. Write the results down as indicated below from the tables^{10} used to calculate the PLH, then add them up. The total is the PLH.

6. Repeat this step using the ** 1000Hz frequency** and the table

7. Repeat this step using the ** 2000Hz frequency** and the table

8. Repeat this step using the ** 3000Hz frequency** and the table

9. Repeat this step using the ** 4000Hz frequency** and the table

10. Now add them up. The sum of 500, 1000, 2000, 3000, and 4000Hz is the PLH. **The total is 2.7% therefore the PLH in this case is 2.7%.**

*Try another example:*

*Using the tables provided below 500Hz to 4000Hz, calculate the PLH of the manual audiogram recorded in Chapter 9.*

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