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Test ID: P50    
Oxygen Dissociation, P50, Erythrocytes

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Useful For Suggests clinical disorders or settings where the test may be helpful

Identifying hemoglobin variants associated with polycythemia disorders

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.

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.

Interpretation Provides information to assist in interpretation of the test results

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.

 

Resulting Cautions:

P50 results will be reported if the shipping control is normal.

 

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.

Clinical Reference 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

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test