## CONVERSION FACTORS

### SI Units

SI (le Système 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).

#### Milliequivalents

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):

Approximate Milliequivalents

 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