### Description

Berlin and Lewis evaluated total red blood cell volume in adults, taking into account different levels of body fat. This can help identify a patient with polycythemia. The authors are from the University of Miami and Hammersmith Hospital in London.

Facts:

(1) The RBC volume in a healthy adult is 35.7 mL per kg lean body weight.

(2) The specific gravity of RBC is 1.094 g/mL (see above).

Parameters:

(1) actual body weight

(2) percent body fat as a decimal fraction

(3) measured (observed) total red cell volume in mL

If the line in Figure 1 is analyzed, the following equation is derived:

normal total RBC volume in mL per kg body weight at a given amount of body fat =

= 35.22 - (33 * (decimal fraction for body fat))

The corresponding equation according to the text appears to be:

normal total RBC volume in mL per kg body weight at a given amount of body fat =

= 35.7 - (34 * (decimal fraction for body fat))

normal total RBC volume in mL for an expected fraction of body fat =

= (body weight in kg) * (total RBC volume)

ratio of measured to normal total RBC volume =

= (measured volume in mL) / (normal volume in mL)

Interpretation:

• If the ratio is > 1.2 (120%) then the patient is polycythemia.