A 34-year-old man is admitted to the hospital with acute chest pain. An ECG is obtained in the emergency department and shows ST segment elevation in leads II, III, and aVF. A sample of blood is taken from the patient, and a new test is used to measure plasma homocysteine levels. The test is repeated 3 times with his blood sample, and the results are 11.8 µmol/L, 9.2 µmol/L, and 13.7 µmol/L (laboratory reference range: 4-14). Which of the following parameters is most likely to be low based on the results of the new test?

Question

A 34-year-old man is admitted to the hospital with acute chest pain.  An ECG is obtained in the emergency department and shows ST segment elevation in leads II, III, and aVF.  A sample of blood is taken from the patient, and a new test is used to measure plasma homocysteine levels.  The test is repeated 3 times with his blood sample, and the results are 11.8 µmol/L, 9.2 µmol/L, and 13.7 µmol/L (laboratory reference range: 4-14).  Which of the following parameters is most likely to be low based on the results of the new test?

Quizplus · Accepted Answer

11ec160b_3732_f3a8_9249_ddfff9f3582e_MD0001_00 A measurement tool should be precise and accurate to be useful in the clinical setting. Precision and accuracy are defined as follows: Precision (reliability) is the ability of a test to reproduce identical or similar results with repeated measurements (bottom half of figure). Accuracy (validity) is the ability of a test to measure what it is supposed to measure. For a new test to be accurate, its results should be equivalent to the results obtained with a "gold standard" (eg, best conventional test available) on the same individual (right half of figure). A precise test gives similar or very close results on repeat measurements. In this example, repeat measurements of the same sample yielded different results; therefore, the new test has low precision. (Choices A and E) To evaluate the accuracy of a new test, its results should be compared to those obtained with the gold standard test on the same individual. A test can be highly precise (ie, gives very similar results on repeat measurements) but inaccurate (ie, the measurements are all incorrect compared to the gold standard). A test that is highly imprecise is also highly inaccurate. In this case, as there were no test results obtained using the "gold standard", the accuracy/validity of the test cannot be determined. (Choices C and D) Sensitivity is defined as a test's ability to identify the true presence of disease, whereas specificity is defined as a test's ability to identify the true absence of disease. Poor reliability can limit the sensitivity or specificity of a test if the results from healthy and diseased populations are close in value. Educational objective: A precise/reliable test is reproducible in that it gives similar results on repeat measurements. Reliability is maximal when random error is minimal.

A 34-Year-Old Man Is Admitted to the Hospital with Acute