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p50

Mnemonic:    [NON-ORDERABLE]
Name:    p50
Specimen:     1 mL collected in a heparinized capped syringe. Deliver to lab ASAP.
  Method:    Spectrophotometric/ Calculation
Note:    Half saturation of hemoglobin by oxygen (p50) indicates the partial pressure of oxygen when oxygen has saturated 50% of the available hemoglobin. The p50 value indicates the position of the oxygen-hemoglobin dissociation curve. A low p50 value shifts the curve to the left and indicates increased oxygen-hemoglobin affinity. High p50 shifts the curve to the right and indicates decreased oxygen-hemoglobin affinity.

The p50 value is useful in indicating the presence of abnormal hemoglobin that affects the oxygen transport mechanism, and is an indirect measure of the 2,3 DPG concentration. pH, pCO2 and temperature can also shift the p50 value.

The p50 value is reported for O2 saturation values between 20% and 90% and is determined as part of a blood gas analysis.
Processing Info:    Run as CO-ox on the blood gas analyzers.