After studying this chapter, you should be able to:
- Briefly describe the importance of biochemical tests in clinical medicine.
- Discuss major considerations to be kept in mind when ordering and interpreting results of laboratory tests.
- Name and have a general understanding of the principal tests used to assess liver, kidney, thyroid, and adrenal function.
Laboratory (lab) tests play an important role in helping physicians and other healthcare workers make diagnoses and other clinical judgments. In this chapter, only biochemical tests (and not hematological, microbiological, immunological, or other types of tests) are discussed, with a few exceptions. In addition, only a brief overview of this subject is presented; medical students will receive much further coverage as they progress through the years of their medical education.
Lab tests constitute only one part of the diagnostic process in clinical medicine. In fact, it has been stated that an experienced physician may arrive at a relatively accurate diagnosis in ˜80% of cases, based solely on a thorough history and physical examination; some may, however, doubt the validity of this statement. However, there is no doubt that, nowadays, biochemical and other lab tests are almost always an important part of the overall diagnostic process. The use of biochemical investigations and lab tests is, however, not confined to diagnoses of diseases. Table 56–1 summarizes some of the different uses of biochemical tests, with examples for each.
Table 56–1 Major Uses of Biochemical Tests with Selected Examples for Each |Favorite Table|Download (.pdf)
Table 56–1 Major Uses of Biochemical Tests with Selected Examples for Each
|Confirm diagnosis of specific diseases||Use of plasma cardiac troponin I (cTI) levels in early diagnosis of myocardial infarction.|
|Suggest rational treatment of disease.||An elevated low-density lipoprotein (LDL) cholesterol level is an indication for therapy with cholesterol-lowering drugs (such as statins) in persons at risk for cardiovascular diseases.|
|Are used as screening tests for the early diagnosis of certain diseases.||Measurement of thyroid stimulating hormone (TSH) levels in neonates helps in diagnosis of congenital hypothyroidism.|
|Assist in monitoring the progress of certain diseases||Serum alanine transaminase (ALT) activity is used to monitor the progress of viral hepatitis|
|Help in assessment of the response of diseases to therapy||In patients with hypo- or hyperthyroidism, measurement of TSH levels helps in monitoring response of patients to treatment.|
|Reveal the fundamental causes and mechanisms of disease||Demonstrate the nature of the genetic defect in cystic fibrosis.|
Two important questions that one should answer prior to ordering any lab investigation are: “What useful information will I get by ordering this test?” and “Will it help the patient?” The concepts discussed in this chapter will contribute to answering these questions and help one make wise use of lab tests in the management of patients.
A myriad of conditions and disorders can lead to abnormalities ...