Estimation of extracellular water by instrumental neutron activation analysis of bromine

Authors: STAMATELATOS, ION - INST NUCLEAR TECH & RADIA; Kehayias, Joseph

Submitted to: Annals of the New York Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2000
Publication Date: 5/1/2000
Citation: Stamatelatos, I.E., Kehayias, J.J. 2000. Estimation of extracellular water by instrumental neutron activation analysis of bromine. Annals of the New York Academy of Sciences. 904:152-3.

Interpretive Summary: The body of an average healthy adult contains 60% water. Body water is divided into two compartments: intracellular (found within the cells) and extracellular. The water balance inside and outside the cells needs to be constant in a human in order to help maintain homeostasis. Test that detect changes in body homeostasis are useful in detecting nutritional status. "Bromine Space Determination" is a test that can detect changes in distribution between these two major water spaces. This test evaluates the bromine concentration in blood before and after the oral administration of a known amount of NaBr. Only a small amount of blood is required and person being tested is not exposed to radiation. The small sample is irradiated with neutrons using a nuclear reactor and then counted for the induced radiation emitted by the Br in the sample.

Technical Abstract: Estimation of the body-water compartments is of great importance in body composition studies. Expansion of the extra-cellular water (ECW) space is a typical characteristic of critical illness and, when measurable, the ratio of intra-cellular to ECW space can serve as an outcome of treatment. Bromine space determination is considered to be as the method, which provides the most accurate non-invasive estimate of ECW. This method requires an evaluation of the apparent Br concentration in plasma. Several workers determined Br levels in plasma using Instrumental Neutron Activation Analysis (INAA). In the present work, we discuss the INAA technique used at "Demokritos" research reactor to estimate Br concentration in plasma samples. Blood samples are collected before and 4 h after (oral or iv) administration of a NaBr solution, at a dose of 25 mg NaBr/kg body weight, from children and adults participating in several fluid imbalance studies. Plasma Br concentration was determined using the Br-79(n, gamma)Br-80 neutron capture reaction and detection of Br-80 gamma-rays at 616.2. A short-time neutron irradiation gamma-ray detection scheme was therefore used at the reactor's pneumatic sample-transfer facility. NaBr comparator standards were used. The corrected bromine space then was calculated from the standard equation using the plasma concentration of Br. Intra-cellular water and cell mass was calculated by subtraction from total body water, which is measured by a stable isotope dilution technique (D2O or O-18). The labeled water is administered together with the NaBr solution and analyzed by mass spectrometry. The accuracy of the technique was checked by determining Br in International Atomic Energy Agency reference blood material. The minimum detection limit of Br in plasma was 0.5 ug/ml, which is an order-of-magnitude below physiological Br levels. Excellent measurement linearity was observed within this Br concentration range. Since no pre-treatment of the sample is required, the technique is practically free of contamination and losses.