Composition of interstitial fluid

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 41; no. 10; pp. 1522 - 1525
• Main Authors: Fogh-Andersen, N, Altura, BM, Altura, BT, Siggaard-Andersen, O
• Format: Journal Article
• Language: English
• Published: Washington, DC Am Assoc Clin Chem 01.10.1995; American Association for Clinical Chemistry
• Subjects: Adult; Analysis of complex biological substances; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Blood and biological fluids; Calcium - blood; Calcium - metabolism; Cations; Erythrocyte Indices; Extracellular Space - metabolism; Female; Fundamental and applied biological sciences. Psychology; Hematocrit; Hemodilution; Humans; Hydrogen-Ion Concentration; Leukocyte Count; Magnesium - blood; Magnesium - metabolism; Male; Middle Aged; Phosphates - blood; Phosphates - metabolism; Platelet Count; Posture; Potassium - blood; Potassium - metabolism; Proteins - metabolism; Reference Values; Space life sciences; Supine Position; Human; Biological fluid; Electrolyte; Interstitial fluid; Hematocrite; Chemical composition; Blood plasma
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/41.10.1522

In several previous experiments to determine the composition of interstitial fluid, the results varied depending on the collecting technique, and the electrolyte concentrations differed from those of a hypothetical ultrafiltrate of plasma. In our approach, since a change of position from standing to supine is accompanied by hemodilution with interstitial fluid, we used the changes in hematocrit and composition of plasma in 20 subjects before and after lying down to calculate the composition of added interstitial fluid. The estimated protein concentration was 20.6 g/L, and the concentrations of total calcium and magnesium were low, in accord with a lower concentration of protein-bound calcium and magnesium. The activity of free cations was also lower, in agreement with a Donnan equilibrium potential of 1 mV across the endothelium. The concentration of leukocytes and platelets decreased according to the hemodilution, implying no escape or mobilization of these elements.