P 50 Calculated

Test Code

Alias/See Also

CPT Codes

p50 calculation, pH (venous), pO2 (venous), O2 Saturation (venous), Methemoglobin, Carboxyhemoglobin

Preferred Specimen

Heparinized venous blood

Minimum Volume
1 mL

Other Acceptable Specimens

Transport Container

Lithium Heparin (green top) tube

Transport Temperature
On ice or refrigerated

Specimen Stability
On ice - 1 hour; Refrigerated - 24 hours

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Clotted samples, frozen, expired stability time


Setup Schedule

Daily upon receipt

Report Available
Upon completion of analysis

Reference Range

P50:                     22.6 - 29.4 mm Hg

pH (venous):       7.32 - 7.42

Methemoglobin:   0.4 - 1.5%

Clinical Significance

 Measuring the strength of oxygen binding to hemoglobin at standard in-vitro conditions is of clinical importance because it is a means of detecting the presence of a mutant hemoglobin with high or low affinity for oxygen. Hemoglobins with markedly altered affinity for oxygen may be the cause of polycythemia or, less commonly, anemia.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.