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 PLHS5. 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 duty5,4,8. 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 basis10,6,9. |
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 test10.
How to calculate the PLH10
Using the tables for the frequencies 500, 1000, 2000, 3000 and 4000Hz respectivelyExample of PLH calculation:
Using the audiogram done today 14/09/2018 and listed numerically in the table 10.110 below:
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 “Contribution to PLH by hearing loss at 0.5kHz in better ear and given hearing loss at 0.5kHz in worse ear” plot the result.
5. Write the results down as indicated below from the tables10 used to calculate the PLH, then add them up. The total is the PLH.
6. Repeat this step using the 1000Hz frequency and the table10 for the “Contribution to PLH by hearing loss at 1000kHz in better ear and given hearing loss at 1000kHz in worse ear” plot the result.
7. Repeat this step using the 2000Hz frequency and the table10 for the “Contribution to PLH by hearing loss at 2000kHz in better ear and given hearing loss at 2000kHz in worse ear” plot the result.
8. Repeat this step using the 3000Hz frequency and the table10 for the “Contribution to PLH by hearing loss at 3000kHz in better ear and given hearing loss at 3000kHz in worse ear” plot the result.
9. Repeat this step using the 4000Hz frequency and the table10 for the “Contribution to PLH by hearing loss at 4000kHz in better ear and given hearing loss at 4000kHz in worse ear” plot the result.
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.