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Conversion Factors

SI Units

SI (le Systéme International d'Unités) units are used in many countries to express clinical laboratory and serum drug concentration data. Instead of employing units of mass (such as micrograms), the SI system uses moles (mol) to represent the amount of a substance. A molar solution contains 1 mol (the molecular weight of the substance in grams) of the solute in 1 L of solution. The following formula is used to convert units of mass to moles (mcg/mL to μmol/L or, by substitution of terms, mg/mL to mmol/L or ng/mL to nmol/L).

Micromoles per Liter (μmol/L)

μmol/L=drug concentration(mcg/mL)×1,000molecular weight of drug(g/mol)


An equivalent weight of a substance is that weight which will combine with or replace 1 g of hydrogen; a milliequivalent is 1/1,000 of an equivalent weight.

Milliequivalents per Liter (mEq/L):

mEq/L=weight of salt(g)×valence of ion×1,000molecular weight of salt

weight of salt(g)=mEq/L×molecular weight of saltvalence of ion×1,000

Approximate Milliequivalents

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Weights of Selected Ions
Salt mEq/g Salt mg Salt/mEq
Calcium carbonate (CaCO3) 20.0 50.0
Calcium chloride (CaCl2 · 2H2O) 13.6 73.5
Calcium gluceptate (Ca[C7H13O8]2) 4.1 245.2
Calcium gluconate (Ca[C6H11O7]2· H2O) 4.5 224.1
Calcium lactate (Ca[C3H5O3]2 · 5H2O) 6.5 154.1
Magnesium gluconate (Mg[C6H11O7]2 · H2O) 4.6 216.3
Magnesium oxide (MgO) 49.6 20.2
Magnesium sulfate (MgSO4) 16.6 60.2
Magnesium sulfate (MgSO4 · 7H2O) 8.1 123.2
Potassium acetate (K[C2H3O2]) 10.2 98.1
Potassium chloride (KCl) 13.4 74.6
Potassium citrate (K3[C6H5O7] · H2O) 9.2 108.1
Potassium iodide (KI) 6.0 166.0
Sodium acetate (Na[C2H3O2]) 12.2 82.0
Sodium acetate (Na[C2H3O2] · 3H2O) 7.3 136.1
Sodium bicarbonate (NaHCO3) 11.9 84.0
Sodium chloride (NaCl) 17.1 58.4
Sodium citrate (Na3[C6H5O7] · 2H2O) 10.2 98.0
Sodium iodide (NaI) 6.7 149.9
Sodium lactate (Na[C3H5O3]) 8.9 112.1
Zinc sulfate (ZnSO4 · 7H2O) 7.0 143.8

Valences and Atomic Weights of Selected Ions

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