Oxygen Dissociation, P50, Erythrocytes
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Abnormal oxygen affinity is demonstrated in the presence of some hemoglobin variants:
-High oxygen affinity causes erythrocytosis
-Low oxygen affinity causes cyanosis
Increased oxygen affinity of hemoglobin, reflected in a low p50, left-shifted oxygen dissociation curve, and loss of normal sigmoidal configuration, are characteristic of many hemoglobin variants that are responsible for polycythemia. Measurement of oxygen affinity is the most important method for diagnosis of these disorders.
Identifying hemoglobin variants associated with polycythemia disorders
Normal: p50=24 to 30 mm Hg (with sigmoidal oxygen dissociation curve)
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
To ensure valid results, the specimen must be < or =72 hours old.
The shipping control specimen is required to adequately interpret these cases, as temperature extremes can impact the integrity of the specimen.
P50 results will be reported if the shipping control is normal. The shipping control is necessary for ensuring valid results. If the specimen is compromised, such as during transport, this often results in an abnormal result in both the control and specimen.
If the shipping control is abnormal and the P50 results are within normal range, the results will be reported; however, a comment will be added to the report indicating that the shipping control was not entirely satisfactory.
The test will be cancelled if the patient specimen and shipping control are both abnormal.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =12 months: 24-30 mm Hg
Reference values have not been established for patients who are <12 months of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
Beutler E: Polycythemia. In Williams Hematology. Sixth edition. Edited by E Beutler, MA Lichtman, BS Coller, TJ Kipps. New York, McGraw-Hill Book Company, 2001, p 689