OBJECTIVE:We tested the hypothesis that creamatocrit, the length of the cream column separated from milk by centrifugation and expressed as a percentage of the length of the total milk column, is a useful measure of the lipid concentration and the energy content of human milk. STUDY DESIGN:Milk samples from 17 mothers of preterm infants were analyzed prospectively, fresh as well as frozen and thawed, for creamatocrit measurement and nutrient composition. RESULTS:Creamatocrit correlated strongly with lipid concentration and energy content of human milk, fresh or frozen and thawed. The energy content can be calculated from the regression equation: Energy (kcal/dl) ϭ 5.99 ϫ creamatocrit (%) ϩ 32.5 for a fresh sample, and energy (kcal/ dl) ϭ 6.20 ϫ creamatocrit (%) ϩ 35.1 for a frozen sample. CONCLUSION:Calculations of energy content from the creamatocrit measurement may be useful for an accurate assessment of energy intake in preterm infants fed human milk.Human milk often is fortified with additives in the nutritional management of preterm infants. Because of the marked variation in the nutrient composition of human milk, 1 the precise energy content of the fortified milk remains unknown. Creamatocrit, the length of the cream column separated from milk by centrifugation and expressed as a percentage of the length of the total milk column, varies with the lipid concentration of milk. 2 We hypothesized that the creamatocrit is a useful measure of the lipid concentration, and hence, of the energy content of human milk. Human milk often is frozen for storage and later thawed before feeding preterm infants. We hypothesized that the freezing and thawing of human milk does not alter the validity of the creamatocrit measurement. To test both these hypotheses, we performed a prospective analysis of human milk, fresh as well as frozen and thawed, for its creamatocrit measurement and nutrient composition. METHODS SamplesWe collected freshly expressed human milk samples from mothers of preterm infants who were hospitalized in the neonatal intensive care unit at Vanderbilt University Medical Center. The study was approved by the Committee for the Protection of Human Subjects-Health Sciences of the Institutional Review Board of Vanderbilt University, and informed consent was obtained from each mother.Each milk sample was mixed well and divided into two aliquots, a fresh aliquot for immediate analysis, and a second aliquot, which was placed in a freezer at Ϫ20°C for 7 days and then thawed at 37°C before analysis. Each aliquot was analyzed for creamatocrit, and for concentrations of lipid, carbohydrate, and protein. Creamatocrit MeasurementA hematocrit centrifuge (International Equipment Co.; Needham Heights, MA), glass capillary tubes (32 ϫ 0.8 mm) (Drummond Scientific Company, Broomall, PA), and a microhematocrit reader (Drummond) were used for the measurement of creamatocrit as described previously.3 Milk was drawn by suction into capillary tubes from a well-mixed sample. The tubes were sealed at one end with clay (Chase Instr...