Can also be written as B-hemoglobin/hemoglobin(B) - US spelling
or B-haemoglobin/haemoglobin - UK spelling

The B here refers to blood.

" ... The definition structure is based on the scientific concept of 'examination' – an examination studies one or more properties of a system (a delimited part of the universe). In a clinical laboratory terminology such as the NPU terminology the system of interest is assumed to be (part of) the patient or the environment, and the NPU definition structure states:

The system studied – the part of the patient that is the object of the examination (blood plasma, pituitary gland, skin, kidney, whole body)."