1. A general method for the development of a blood volume index was devised to allow inter-individual comparisons.
2. An accurate and acceptable blood volume index had to fulfil certain criteria; it had to be (1) not correlated with body size, (2) highly correlated with blood volume, (3) either dimension-less or expressible in units of length or of surface area and (4) simple to calculate.
3. Available data, from the Broussais Hospital, Paris, the Zuiderziekenhuis, Rotterdam and the Cleveland Clinic, Cleveland, Ohio, included six groups of normal subjects, male essential hypertensive patients and female essential hypertensive patients.
4. Extensive calculations, based on the available data, indicated that the equation BVI = BV/(a√H.W) (BVI = blood volume index, BV = blood volume, H = body height, W = body weight and a = a constant depending on the chosen units) was the simplest index which satisfied the above requirements.
5. As the equation SA = 0.165 √(H.W) (SA = body surface area, in m2, H in m and W in kg) is almost identical with the Dubois & Dubois formula predicting body surface area from height and weight, one may choose a = 0165 and the index BVI = BV/[0.165 √(H.W)] (/H in m, W in kg, BV in ml and BVI in ml/m2). Thus blood volume is referred to body surface area.
6. Blood volume referred to unit body surface area appears, at the present, to be the most appropriate ‘blood volume index’. However, studies of data from larger groups and from more centres are needed to confirm this conclusion.