Interpretation of Anemia with Elevated Reticulocyte Count and Hyponatremia

Introduction to Anemia and Hyponatremia

The American College of Physicians suggests that a combination of anemia with a slightly elevated reticulocyte count and persistent hyponatremia at 125 mmol/L with normal urine osmolality suggests hemolytic anemia with possible syndrome of inappropriate antidiuretic hormone secretion (SIADH) or another cause of hyponatremia that requires separate evaluation 1

Elevated reticulocyte count with anemia indicates the bone marrow is responding appropriately to either blood loss or red cell destruction (hemolysis) 1
The slightly elevated reticulocyte count excludes deficiency states (iron, B12, folate) as the primary cause of anemia 1
Reticulocyte index (RI) should be calculated to correct the reticulocyte count against the degree of anemia to determine if bone marrow response is appropriate 1

Evaluate for hemolysis by checking haptoglobin levels (decreased in hemolysis), lactate dehydrogenase (elevated in hemolysis), and indirect bilirubin (elevated in hemolysis) 1
Peripheral blood smear to assess for red cell morphology abnormalities is recommended by the American Society of Hematology 2
Common causes of hemolytic anemia with elevated reticulocytes include autoimmune hemolytic anemia, hereditary hemolytic anemias, and mechanical hemolysis 1, 2

Persistent hyponatremia (Na 125 mmol/L) with normal urine osmolality (470 mmol/kg) requires separate investigation, according to the National Kidney Foundation 3
Normal urine osmolality in the setting of hyponatremia suggests inappropriate water retention, possibly due to SIADH, hypothyroidism, adrenal insufficiency, or medication effect 3

Consider chronic kidney disease as it can cause both anemia and electrolyte abnormalities, as suggested by the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines 4, 3

Complete the hemolysis workup with peripheral blood smear, direct antiglobulin test (Coombs), haptoglobin, LDH, and bilirubin, as recommended by the American College of Physicians 1
Evaluate iron status with serum ferritin and transferrin saturation, according to the National Institute of Diabetes and Digestive and Kidney Diseases 4
Check thyroid function tests to rule out hypothyroidism as a cause of hyponatremia, as suggested by the American Thyroid Association 3
Assess kidney function with creatinine and estimated GFR, according to the National Kidney Foundation 4
Consider specialized testing for hereditary hemolytic anemias if initial workup suggests this etiology, as recommended by the American Society of Hematology 2
Evaluate volume status to help differentiate causes of hyponatremia, according to the European Society of Intensive Care Medicine 3

Don't assume a slightly elevated reticulocyte count always indicates adequate bone marrow response; calculate the reticulocyte index to correct for degree of anemia, as suggested by the American College of Physicians 1
Don't overlook the possibility of combined etiologies - the anemia and hyponatremia may be related or separate issues, according to the National Institute of Diabetes and Digestive and Kidney Diseases 1
Don't forget to evaluate for occult blood loss as a cause of anemia with elevated reticulocytes, as recommended by the American College of Gastroenterology 1