The conventional units in this table are the ones most commonly used in the United States. Outside the United States, SI units are the predominant nomenclature for laboratory test results. The base units in the SI system related to laboratory testing that are found in this table include the mole (amount of substance), meter (length), kilogram (mass), second (time), and Celsius (temperature).
Reference ranges vary depending on the instrument and the reagents used to perform the test. Therefore, the reference ranges shown in this table are only close approximations to the adult reference ranges found in an individual clinical laboratory. For example, coagulation tests measured in seconds until a clot forms in the tube, such as the PT and the PTT, have reference ranges that are affected by both the instrument and the reagents used to perform the test. There are more than 100 possible combinations of coagulation instruments and reagents, and, therefore, there are at least 100 different reference ranges, which are mostly similar but not identical. The cutoff value for troponin for acute myocardial infarction is at the 99th percentile of a reference range which is also instrument and reagent dependent. In addition, it is important to understand that reference ranges can be significantly affected by age and sex.
The table contains information about selected drugs for which there is no reference range because they are not present in the circulation of those not taking the drug. However, drugs which are monitored have therapeutic levels, and some of these are included in the list of reference ranges. The therapeutic range for a drug is most often established by the concentration of the drug just prior to administration of the next dose. This is called the trough level. For other drugs, the therapeutic range refers to its range at peak concentration. This varies from drug to drug and is dependent upon many factors, such as absorption, distribution within the body, and metabolism of the drug. The table does not indicate whether the therapeutic level is a peak or a trough level.
Also listed in the table are selected compounds which are neither drugs nor laboratory tests, but are compounds which can be measured in the blood and, at some concentration, become toxic. For these listings, the compound is named and the word (toxic) is listed on the same line.
Conversion factors are provided in the table to allow the reader to convert conventional units to SI units and vice versa. The conversion of the conventional unit to SI unit requires a multiplication with the conversion factor, and conversion of the SI unit to the conventional unit requires division by the conversion factor.
The sample fluid is sometimes highly restrictive. For example, coagulation tests must be performed using plasma samples. Serum samples are unacceptable. For other compounds, both plasma samples and serum samples may be acceptable. However, there may be differences, often ...