The present invention relates to method for providing values of measured and/or estimated arterial oxygenation (SO2AM, SO2AE, SpO2) based on measuring values of blood acid/base status in a venous blood sample (VBGM, VBGE). A conversion of the venous blood values is made by applying a mathematical model for deriving blood acid/base status and oxygenation status into estimated or predicted arterial blood values (ABGP). Furthermore, if a value of measured and/or estimated arterial oxygenation value is below a corresponding venous oxygenation value, then estimating the arterial oxygenation value is made with a replacement value being a function of the corresponding venous oxygenation value. The advantage is that converting venous blood value to arterial blood values will be possible by providing arterialized blood gas and acid-base values for a higher percentage of clinical samples previously not possible.
