Ovid: 5-Minute Sports Medicine Consult, The

Michelle Burke
Julie M. Kerr
  • Dilutional phenomenon in endurance athletes causing hemoglobin and hematocrit values that are lower than established limits of normal
  • Plasma volume expansion by 10–20% with little change in red cell numbers (ie, oxygen-carrying capacity; red cell mass remains unchanged) (1)
  • Contributing factors include:
    • Exercise-induced release of aldosterone, renin, and vasopressin
    • Increased size of vascular bed owing to muscle hypertrophy
    • Retention of crystalloids and colloids governed by hormones
  • Theoretically, this increased blood volume decreases viscosity, thereby maximizing stroke volume, cardiac output, and subsequent oxygen delivery (2).
  • Hemodilution occurs over the 48 hr after every episode of endurance exercise and may persist for as long as 1 wk after discontinuing training.
  • If training continues, red cell mass will catch up with plasma volume expansion over the span of few weeks, causing hemoglobin and hematocrit values to normalize (3).
  • Synonym(s): Sports anemia; Athletes' pseudoanemia
  • Elite athletes involved in endurance training
  • Previously sedentary individuals starting an exercise program
  • Athletes increasing intensity of training
Check exercise schedule, type of training activity, and occurrence of any symptoms.
Physical Exam
  • Hemoglobin levels 13–14 g/100 mL in men and 11–12 g/100 mL in women; dose-response relationship between amount/intensity of exercise and hemoglobin drop (4)
  • Elite endurance athletes have a greater degree of dilutional pseudoanemia than more moderate endurance athletes.
  • Females are more likely than males to have iron-deficiency anemia with sports ± presence of pseudoanemia.
  • No particular symptoms or physical findings


Diagnostic Tests & Interpretation
  • Laboratory studies are performed if etiology unclear or symptoms are present.
  • Normal mean corpuscular volume
  • No hematuria or hemoglobinuria on urinalysis
  • Normal bilirubin and haptoglobin
  • Ferritin may be lower in endurance athletes owing to the same relative dilutional effect. Values often <60 µg/L, occasionally <30, but <15 = iron deficiency.
Differential Diagnosis
  • Iron-deficiency anemia
  • GI bleeding
  • Hematuria
  • Foot-strike hemolysis
285.9 Anemia, unspecified

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