Chemical pathology

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Chemical pathology (also known as clinical biochemistry or clinical chemistry) is the area of pathology that is generally concerned with analysis of bodily fluids.

The discipline originated in the late 19th century with the use of simple chemical tests for various components of blood and urine. Subsequently other techniques were applied including the use and measurement of enzyme activities, spectrophotometry, electrophoresis and immunoassay.

Most current laboratories are now highly automated and use assays that are closely monitored and quality controlled.

Tests that require examination and measurement of the cells of blood, as well as blood clotting studies, are not included as in the UK these are usually grouped under hematology, but in many countries these specialties along with immunology and microbiology are grouped under laboratory medicine.

All biochemical tests come under chemical pathology. These are performed on any kind of body fluid, but mostly on serum or plasma. Serum is the yellow watery part of blood that is left after blood has been allowed to clot and all blood cells have been removed. This is most easily done by centrifugation which packs the more dense blood cells and platelets to the bottom of the centrifuge tube, leaving the liquid serum fraction resting above the packed cells. Plasma is essentially the same as serum, but is obtained by centrifuging the blood without clotting. Plasma therefore contains all of the clotting factors, including fibrinogen.

A large laboratory will accept samples for up to about 700 different kinds of tests. Even the largest of laboratories rarely does all these tests themselves and some need to be referred to other labs.

This large array of tests can be further sub-categorised into sub-specialities of: