Sensitivity, Specificity, PPV, NPV

Sensitivity is TRUE POSITIVE RATE.

2x2 table 

Sensitive test picks all diseased and also sometimes without disease. That means it won’t miss the disease.

Sensitivity is a measure of  test positive out of total diseased. 

Specificity is TRUE NEGATIVE RATE.

Specific test picks only the diseased one but may sometime miss the disease itself.

Sensitivity and specificity are not dependent upon the disease prevalence rate.

Specificity is measure of true negative out of total healthy patient. 

Predictive values depend upon the prevalence of disease and accuracy of the test.

Positive Predictive Value is the proportion of the people with positive test who actually have disease.

Negative Predictive Value is the proportion of the people with negative test who actually do not have disease.

	PPV	NPV
Definition	% that a person with positive test is actually diseased.	% change that a person with negative test is actually disease free.
Use	Proceed with a patient with positive test	Proceed with a patient with negative test
Relation to prevalence	Low prevalence low PPV High prevalence high PPV	High prevalence low NPV Low prevalence High NPV

Test for Malingering or NOHL (Non Organic Hearing loss)

Suspect when someone shows exaggerated efforts to hear.

Cups around the ear and requests to repeat the question.

Learn how hearing is tested in normal patients.

Tuning Fork Test
STENGER TEST: It is based on the fact that if two tuning forks with same frequency are placed on two sides of the head, the one with the highest intensity is only heard. We need a pair of tuning forks which are placed 25cm from the head and the patient is blindfolded. The malingerer will say he hears on the normal ear. Now the Tuning fork on the side of the defective ear will be brought ahead at 8cm. This time the patient hears the sound but will say he did not hear anything. But if he is genuine he will hear on the normal side.

TEAL TEST: If someone claims of having conductive hearing loss we use this technique. Blindfold the patient and place the tuning fork over mastoid. He claims of hearing. Say you are repeating the test. And place one vibrating tuning fork in front of the ear and next non-vibrating tuning fork over the mastoid. Malingerer will say he hears the sound but the genuine one would not.

Pure Tone Audiometry (PTA) and Speech Discrimination Score (SDS)

·         Inconsistence in results of PTA or when repeated over and over. Variation in results greater than 15dB is diagnostic for NOHL.

·         Inconsistency in PTA and SRT results by 10dB.

·         Generally Shadow Curve is present if CHL is greater than 40dB and if the healthy ear is not masked. Absence means NOHL.

Delayed Speech Feedback
We need a tape recorder and playback system with delaying capacity. The patient is given a book to read and the same is played to his ear with slight delay of around 110-300ms in the (so called) defective ear. In a genuine patient there is no pausing but in real malingerers there will be stammering because our voice production depends upon what we hear. So he gets confused with the variable sound in two sides of the ear.

LOMPARD TEST
 As stated earlier sound of our own voice is necessary for proper regulation of its tone and loudness. Barany box is placed in the patient's sound ear. The patient is asked to read the book aloud and the Barany box is played on and patient is asked to continue. If one has profound hearing loss he will raise his volume. But malingerer claiming of Unilateral Deafness will continue reading.

Acoustic reflex Threshold/ Stapedial Reflex

Reflex is elicited but the patient claims of hearing loss. This means he is feigning.

Electric Response Audiometry

Source: PL Dhingra and Logan and Turner ENT Textbooks