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Milliequivalent and millimole calculations and conversions

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Definitions & calculations
Valences and atomic weights of selected ions
Milliequivalents
Definitions and equations
Osmolality
Bicarbonate deficit
Anion gap
Reticulocyte index

Definitions & calculations
  • Note: Use of equivalents and milliequivalents is valid only for those substances that have fixed ionic valences (e.g. sodium, potassium, calcium, chlorine, magnesium bromine, etc). For substances with variable ionic valences (e.g. phosphorous), a reliable equivalent value cannot be determined. In these instances, one should calculate millimoles (which are fixed and reliable) rather than milliequivalents.

Valences and atomic weights of selected ions
  • Note: The molecular weight of phosphorus only is approximately 31 grams, and sulfur only is 32 grams.

Milliequivalents
  • Milliequivalent conversation equations are shown in the table below. Selected approximate milliequivalents and weights of selected ions are also listed below.

Definitions and equations
  • Select abbreviations, definitions, and disorders listed below.

Osmolality
  • Osmolality: The summed concentrations of all osmotically active solute particles
  • Normal range: 285-295mOsm/L
  • Predicted serum osmolality: 2 Na+ + (glucose (mg/dL) / 18) + (BUN (mg/dL) / 2.8)
  • Differential diagnosis of increased serum osmolal gap (>10mOsm/L): medications and toxins, alcohols (ethanol, methanol, isopropanol, glycerol, ethylene glycol), mannitol.
  • Osmolal gap = measure Osm - calculated Osm
  • Normal: 1 to 10
  • Abnormal: >10
  • Probably lab or calculation error: <0

Bicarbonate deficit
  • HCO3- deficit = (0.4 x wt in kg) x (HCO3- desired - HCO3- measured)
  • Note: In clinical practice, the calculated quantity may differ markedly from the actual amount of bicarbonate needed or that which may be safely administered.

Anion gap
  • Anion gap: The difference in concentration between unmeasured cation and anion equivalents in serum.
  • Anion gap = Na+ - (Cl + HCO3-)
  • The normal anion gap is 10-14mEq/L
  • Differential diagnosis of increased anion gap acidosis: organic anions, lactate (sepsis, hypovolemia, seizures, large tumor burden), pyruvate, uremia, ketoacidosis (hydroxybutyrate and acetoacetate), amino acids and their metabolites, other organic acids, inorganic anions, hyperphosphatemia, sulfates, nitrates.
  • Differential diagnosis of decreased anion gap: organic cations, hypergammaglobulinemia, inorganic cations, hyperkalemia, hypercalcemia, hypermagnesemia, medications and toxins, lithium, hypoalbuminemia.

Reticulocyte index
  • (% reticulocyte / 2) x (patient's Hct / normal Hct) or (% reticulocyte / 2) x (patient's Hgb / normal Hgb)
  • Normal index = 1.0
  • Good marrow response = 2.0 - 6.0

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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