Hypophosphatemia

Background

• Phosphate required in function of all hematologic cells (RBCs, WBCs, platelets)

Clinical Features

• CNS
  • Weakness
  • Circumoral and fingertip paresthesias
  • Decreased DTRs
  • Decreased Mental Status
• Cardiac
  • Impaired myocardial function

Differential Diagnosis

Causes of Hypophosphatemia

• Internal redistribution
  • Refeeding of malnourished
  • DKA
  • Nonketotic hyperglycemia
  • Receiving hyperalimentation
  • Acute respiratory alkalosis
  • Hungry bone syndrome
• Decreased intestinal absorption
  • Inadequate intake
  • Antacids containing aluminum or magnesium
  • Steatorrhea and/or chronic diarrhea
• Increased urinary excretion
  • Vitamin D deficiency or resistance
  • Primary renal phosphate wasting (rare genetic disorders)
  • Fanconi syndrome
    • Multiple myeloma
  • Osmotic diuresis (most often due to glucosuria)
  • Proximally acting diuretics (e.g. acetazolamide and some thiazide diuretics)
  • Acute volume expansion
  • Intravenous iron administration
• Renal replacement therapy (dialysis)

Evaluation

• 2.5-2.8 Mild
• 1.0-2.5 Moderate
• <1.0 Severe

Management

• Mild-moderate
  • KPhos /neutra phos PO
• Severe
  • KPhos 2.5-5mg/kg IV over 6hr

Harbor UCLA Adult Treatment Guidelines

Serum phosphate 1mg/dl to 2mg/dl

• Able to take PO
  • Minimize or eliminate all dextrose-containing IV solutions
  • Aggressively treat acidosis
  • 1 tab K-phos neutral 250mg Q hour x 5 doses
    • Each tab contains phosphorus 8 mmol, Na 13 mEq, K1.1 mEq
  • Recheck serum phosphate after last dose, and repeat dosing if continues to be <2mg/dl
• NOT able to take PO
  • Minimize or eliminate all dextrose-containing IV solutions
  • Aggressively treat acidosis
  • Give 15 mmol of IV potassium phosphate over 2.5 hours (contains 22 mEq K)
    • Peripheral administration may cause burning at injection site
    • Consider central venous administration, if available
    • Repeat dosing regimen if serum phosphate remains <2mg/dl

Serum phosphate <1mg/dl

• Minimize or eliminate all dextrose-containing IV solutions
  • Exceptions: vasopressors, sedatives, analgesics, antibiotics, blood products, NS
• Aggressively treat acidosis
• Give 45 mmol of IV potassium phosphate over 7 hours (contains 66 mEq of K)
  • Peripheral administration may cause burning at injection site
  • Consider central venous administration, if available
• If patient can tolerate PO, ALSO follow steps 1 above
• Recheck serum phosphate after infusion
  • Repeat IV administration if <1mg/dl
  • Consider oral administration if >1mg and <2mg/dl

See Also

• Electrolyte Abnormalities (Main)