Complete Blood Count (CBC)

The cell measurements are related. For example, haemoglobin is interpreted with red cell size and count, while a white cell change may need the differential to explain it.

A high white cell count most often reflects infection or inflammation, which also shifts the breakdown of the different white cell types. Strenuous exercise just before the test and acute stress can raise it briefly. Less often, a bone marrow disorder produces cells in excess, which is why a persistent or unusual rise may lead to a blood film.

A low platelet count can follow medicines that suppress the bone marrow, autoimmune destruction of platelets or an enlarged spleen that holds cells out of circulation. It can also be a false result: a clotted or underfilled sample can lower the measured count. An unexpected low result is therefore usually repeated before your doctor draws conclusions.