Measurement of Blood Volume in Adult Rhesus Macaques (Macaca mulatta)

Abstract

Most biomedical facilities that use rhesus macaques (Macaca mulatta) limit the amount of blood that may be collected for experimental purposes. These limits typically are expressed as a percentage of blood volume (BV), estimated by using a fixed ratio of blood (mL) per body weight (kg). BV estimation ratios vary widely among facilities and typically do not factor in variables known to influence BV in humans: sex, age, and body condition. We used indicator dilution methodology to determine the BV of 20 adult rhesus macaques (10 male, 10 female) that varied widely in body condition. We measured body composition by using dual-energy X-ray absorptiometry, weight, crown-to-rump length, and body condition score. Two indicators, FITC-labeled hydroxyethyl starch (FITC-HES) and radioiodinated rhesus serum albumin ((125)I-RhSA), were injected simultaneously, followed by serial blood collection. Plasma volume at time 0 was determined by linear regression. BV was calculated from the plasma volume and Hct. We found that BV calculated by using FITC-HES was consistently lower than BV calculated by using (125)I-RhSA. Sex and age did not significantly affect BV. Percentage body fat was significantly associated with BV. Subjects categorized as having 'optimal' body condition score had 18% body fat and 62.1 mL/kg BV (by FITC-HES; 74.5 mL/kg by (125)I-RhSA). Each 1% increase in body fat corresponded to approximately 1 mL/kg decrease in BV. Body condition score correlated with the body fat percentage (R(2) = 0.7469). We provide an equation for calculating BV from weight and body condition score.

Figure 1.

The 2014 blood volume collection guidelines from each of the 8 National Primate Research Centers in the United States.

Figure 2.

(A) Correlation between BV (mL) amounts obtained using the 2 methods: FITC–HES and ¹²⁵I-RhSA. (B) This Altman–Bland plot shows the difference relative to the average between the 2 methods of determining BV. The difference between the methods was consistent across the range of blood volumes in the study group. The average difference was 12.95 mL/kg, with bias toward a larger calculated BV with ¹²⁵I-RhSA method.

Figure 3.

Mean BV (mL/kg) for male and female rhesus macaques using 2 methods, ¹²⁵I-RhSA and FITC–HES. There was no sex-associated difference in BV. Error bars, SEM.

Figure 4.

The influence of age (y) on BV (mL/kg) was assessed by using Pearson correlation for (A) ¹²⁵I-RhSA and (B) FITC–HES. Trends toward decreasing BV with increasing age were not statistically significant in the study group (age: mean, 12.5 y; range, 5.7 to 17.6 y).

Figure 5.

Correlation between BV and percentage body fat (Fat%), obtained via DXA. Total BV was measured by both the radioactive ¹²⁵I-RhSA method (squares) and the nonradioactive FITC–HES method (circles). For both methods, BV and percentage body fat were significantly negatively related (P < 0.0001 for both).

Figure 6.

Average percentage body fat for each body condition score. The correlation indicates that the BCS can be used as a surrogate for body fat percentage in adult rhesus macaques.

Figure 7.

(A) Correlation between measured BV (FITC–HES method) and BV predicted by using equation 3. (B) The Altman–Bland plot shows reasonable agreement between the measured and predicted BV.