Merck Manual

Please confirm that you are a health care professional

honeypot link
  • Ready Reference Guides
    In the US, most laboratory test results are reported in what are termed conventional units; the rest of the world reports results in Système International d’Unités (SI) or international units (IU). The unit basis for SI is updated periodically by a panel.

  • Normal Laboratory Values
    Reference values (intervals) for blood, urine, cerebrospinal fluid (CSF), stool, and other fluids (eg, gastric acid) and commonly used panels are included. (NOTE: The reference values provided in these tables should be used as guidelines only.) Reference values vary based on several factors, including the demographics of the healthy population from which specimens were obtained and the specific methods and/or instruments used to assay these specimens. Laboratories that are accredited by the College of American Pathologists (CAP) are required to establish and/or validate their own reference values. Thus, any given result should be interpreted based on the reference value of the laboratory in which the test was done. The laboratory typically provides these values with the test result. Reference values on other types of body fluids (eg, synovial, peritoneal, pleural, pericardial) have not been widely established. Therefore, these tests may be considered Laboratory Developed Tests (LDTs). Analyte reference ranges from LDTs are established by the individual laboratory doing the testing and typically vary more than reference values do.