Equations and nomogram for the relationship of human blood p50 to 2,3-diphosphoglycerate, CO2, and H+

M. Samaja, A. Mosca, M. Luzzana, L. Rossi-Bernardi, R. M. Winslow

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We describe a new method for tonometry of small amounts of blood (up to 0.25 mL) at known p(O2), p(CO2), and temperature, in small, reusable, closed Pyrex flasks. Equilibrated blood is analyzed for oxygen saturation, pH, and organic phosphate concentration with standard techniques, and its p50 (the p(O2) at which hemoglobin is half-saturated with oxygen) is determined with full control of all the variables known to affect it. The SD in the measurement of p50 is 0.044 kPa (0.33 mmHg). We made 63 determinations of p50 on normal human blood under different conditions of pH and p(CO2), and with diferent concentrations of 2,3-diphosphoglycerate and ATP. Empirical equations and a nomogram were derived, which allow the calculation of p50 from known values of p(CO2), pH, and [2,3-DPG]/[Hb4] molar ratio with a SD of 97 and 114 Pa (0.73 and 0.86 mmHg), respectively.

Original languageEnglish
Pages (from-to)1856-1861
Number of pages6
JournalClinical Chemistry
Issue number11
Publication statusPublished - 1981


ASJC Scopus subject areas

  • Clinical Biochemistry

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