A 35-year-old Caucasian female presents to the office due to a self-palpated breast mass. After the appropriate work-up, fine-needle aspiration (FNA) of the mass is performed. The results of the FNA return as negative. As you are explaining the test result, the patient asks, "What are the chances that I really do not have breast cancer?" Which of the following values best addresses this patient's question?

Question

A 35-year-old Caucasian female presents to the office due to a self-palpated breast mass.  After the appropriate work-up, fine-needle aspiration (FNA) of the mass is performed.  The results of the FNA return as negative.  As you are explaining the test result, the patient asks, "What are the chances that I really do not have breast cancer?"  Which of the following values best addresses this patient's question?

Quizplus · Accepted Answer

The negative predictive value (NPV) is defined as the probability of being free of a disease if the test result is negative. One very important thing to remember is that the NPV will vary with the pretest probability of a disease. A patient with a high probability of having a disease will have a low NPV, and a patient with a low probability of having a disease will have a high NPV. Specific examples are given below: the NPV will vary with the pretest probability of a disease 1) Breast cancer and FNA test results A patient with a high pre-test probability for having breast cancer (e.g., female, has first degree relatives with breast cancer, greater than 40 years old) has a low NPV. A patient with a low pre-test probability of having breast cancer (e.g., less than 40 years old, as in this case) has a high NPV. A patient with a high pre-test probability for having breast cancer (e.g., female, has first degree relatives with breast cancer, greater than 40 years old) has a low NPV. A patient with a low pre-test probability of having breast cancer (e.g., less than 40 years old, as in this case) has a high NPV. 2) HIV and ELISA test results A patient who belongs to a high-risk group (e.g., multiple sexual partners, admits to not using condoms, IV drug user) has a high pre-test probability; consequently, this patient will have a low NPV. On the other hand, a patient who belongs to a low-risk group (e.g., one sexual partner who has no other sexual partners, uses condoms correctly all the time, no history of IV drug use) has a low pre-test probability; consequently, this patient will have a high NPV. A patient who belongs to a high-risk group (e.g., multiple sexual partners, admits to not using condoms, IV drug user) has a high pre-test probability; consequently, this patient will have a low NPV. On the other hand, a patient who belongs to a low-risk group (e.g., one sexual partner who has no other sexual partners, uses condoms correctly all the time, no history of IV drug use) has a low pre-test probability; consequently, this patient will have a high NPV. *Note: The prevalence of a disease is directly related to the pre-test probability of having the disease, and also affects the NPV. (Choices A and B) The sensitivity and specificity of a test are fixed values which do not vary with the pretest probability of a disease. Most researchers agree that the ideal diagnostic test should have high sensitivity and specificity. In this case, FNA also has a high sensitivity and specificity; however, the statistical parameter being described by the patient and physician was the high negative predictive value. fixed values (Choice C) The positive predictive value follows the same concept, but applies if the test result is positive. (Choice E) Validity represents the appropriateness of the test (i.e., the test measures what it is supposed to measure). It does not depend on the pretest probability of the disease. Educational Objective: NPV is the probability of being free of a disease if the test result is negative. Remember: the NPV will vary with the pretest probability of a disease. A patient with a high probability of having a disease will have a low NPV, and a patient with a low probability of having a disease will have a high NPV. the NPV will vary with the pretest probability of a disease

A 35-Year-Old Caucasian Female Presents to the Office Due to a Self-Palpated