[Decision analysis and clinical laboratory test in general internal medicine]

We demonstrated the quantitative approach to evaluating laboratory test in a patient with hypercalcemia.

43 year-old-woman was referred to our department because of sustained hypercalcemia without subjective symptoms in the past 5 years. Physical examination showed no abnormality with laboratory tests unremarkable except for hypercalcemia (10.8 mg/dl). DIFFERENTIAL DIAGNOSIS AND PRE-TEST PROBABILITY SETTING: Based on history and physical examination, we hypothesized two possible cases of hypercalcemia; primary parathyroidism (PHP) malignant disease (MD). The pre-test probability of PHP was set at 1/3, and that of MD at 2/3. CALCULATION AND ASSESSMENT: The post-test probability using the likelihood ratio of "albumin > 4.0 g/dl", 5.1 was increased to 0.72. However, it was not considered above the test-treatment threshold. We then measured Intact PTH which has a likelihood ratio 14. Intact PTH was increased yielding the post-test probability of 0.97. We considered that this value exceeded test-treatment threshold. The patient was referred to a surgical department.

In daily practice, we, internists have to make clinical decisions quantitatively based on test results. To make a rational and quantitative approach to diagnostic tests clinical routine, it is mandatory to determine sensitivity and specificity of all laboratory tests used in our country.