Hemoglobin, Elevated
(Polycythemia or Erthrocytosis)
Update September 16, 2018
Polycythemia is an increase above the normal range of RBCs in the circulation. Concern that the Hb level may be abnormally high should be triggered at a level of 170 g/L (17 g/dL) in men and 150 g/L (15 g/dL) in women. Polycythemia is usually found incidentally at routine blood count.
Relative erythrocytosis, due to plasma volume loss (e.g., severe dehydration, burns), does not represent a true increase in total RBC mass. Absolute erythrocytosis is a true increase in total RBC mass.
An approach to the differential diagnosis of pts with an elevated hemoglobin (possible polycythemia). AV, atrioventricular; COPD, chronic obstructive pulmonary disease; EPO, erythropoietin.
COMPLICATIONS
Hyperviscosity (with diminished O2 delivery) with risk of ischemic organ injury and thrombosis (venous or arterial) are most common.
TREATMENT: POLYCYTHEMIA
Phlebotomy recommended for Hct ≥55%, regardless of cause, to low-normal range. Aspirin is routinely given to lower the thrombosis risk.
CAUSES
Polycythemia vera (a clonal myeloproliferative disorder), erythropoietin-producing neoplasms (e.g., renal cancer, cerebellar hemangioma), chronic hypoxemia (e.g., high altitude, pulmonary disease), carboxyhemoglobin excess (e.g., smokers), high-affinity Hb variants, Cushing’s syndrome, androgen excess. Polycythemia vera is distinguished from secondary polycythemia by the presence of splenomegaly, leukocytosis, thrombocytosis, and elevated vitamin B12 levels, and by decreased erythropoietin levels and the presence of a mutation in the JAK2 kinase (V617F). An approach to evaluate polycythemic pts is shown in Fig. 45-2.
1. History
| Item or Symptom | Possible Condition |
|---|---|
3. Lab Test
| Item or Lab Test | Possible Condition |
1. increased red cell mass (using the principle of isotope dilution by administering 51Cr-labeled autologous red blood cells to the patient and sampling blood radioactivity over a 2-h period.) (>36 mL/kg in men, >32 mL/kg in women), |
Polycythemia Vera |
Red cell mass is normal (<36 mL/kg in men, <32 mL/kg in women), |
Spurious or relative polycythemia. |
If serum EPO levels are elevated, one needs to distinguish whether the elevation is a physiologic response to hypoxia or related to autonomous EPO production. Patients with low arterial O2 saturation (<92%) should be further evaluated for the presence of heart or lung disease, if they are not living at high altitude. Patients with normal O2 saturation who are smokers may have elevated EPO levels because of CO displacement of O2. If carboxyhemoglobin (COHb) levels are high, the diagnosis is “smoker’s polycythemia.” Such patients should be urged to stop smoking. Those who cannot stop smoking require phlebotomy to control their polycythemia. Patients with normal O2 saturation who do not smoke either have an abnormal hemoglobin that does not deliver O2 to the tissues (evaluated by finding elevated O2–hemoglobin affinity) or have a source of EPO production that is not responding to the normal feedback inhibition. Further workup is dictated by the differential diagnosis of EPO-producing neoplasms. Hepatoma, uterine leiomyoma, and renal cancer or cysts are all detectable with abdominopelvic computed tomography scans. Cerebellar hemangiomas may produce EPO, but they present with localizing neurologic signs and symptoms rather than polycythemia-related symptoms. |
|
A 55-year-old man presents to his family physician because of complaints of headaches and difficulty concentrating. He has also noticed an intermittent, slightly pink discoloration of his urine. A CBC reveals hemoglobin of 21.0 g/dL and normal white blood cell and platelet counts. Which of the following tests is most likely to detect the source of his symptoms?
The correct answer is D.
The patient is experiencing symptoms from sluggish blood flow due to the high red blood cell count. The pink discoloration of the urine is due to blood. The elevated red blood cell count is due to abnormal erythropoietin production. Both of these features indicate a renal cell carcinoma, which, of the above choices, would be diagnosed with a CT scan of the abdomen and pelvis.