Calculations

There are a some very core equations you'll want to just KNOW for your certification exam. I've tried to remember which seemed the most vital. There are many others, of course. But you should probably know at least these. Also, remember that the normal ranges may be slightly different depending on where you work. But, you should know the general ballpark and be able to tell if a result is very high or low.

Miscellaneous

Note: Low CV = High Precision

Chemistry

Henderson-Hasselbalch Equation:      or            (pKa=6.1)
HCO3- = Bicarb    H2CO3 = Carbonic Acid
H2CO3 = PCO2 * 0.03
Total CO2 = HCO3- + H2CO3
     or
Partial Pressure = Barometric Pressure * % Gas Concentration

TDM

Therapeutic Index = (MTC=Min. Toxic Concentration; MEC = Min. Effective Concentration)

Spectrophotometry

A=2-log%T
Beer’s Law: A=ebc or

Other

	Equation	Normal Range	Notes
Albumin to Globulin Ratio		1-2.5	Reversed A/G Ratio in M.M.
Anion Gap	(Na + K) – (Cl + CO2)	10-20mEq/L	↑acute pancreatitis ↓macroamylasemia
BUN to Creatinine Ratio		12-20	High Ratios indicate prerenal or postrenal azotemia
Creatinine Clearance (mL/min)		Male: 97-137 Female: 88-128	↓Renal Disease (Early Indicator)
LDL Cholesterol		Want <130 mg/dL	Trig must be <400mg/dL ↑LDL = risk of CAD
Osmolality		275-295	[solute]; one of the colligative properties
Osmolal Gap	Measured Osm. – Calculated Osm.	0-10 mOsm/kg	>10 indicates abnormal concentration of an unmeasured substance
Urine/Serum Osmolality		1.0-3.0	↓ renal tubular deficiency, diabetes insipidus
Volume & Concentration	V1C1 = V2C2

Hematology

	Equation	Normal	Notes
MCV		Male: 80-94 fL Female: 81-99 fL	Use to classify anemias >100 macrocytic <80 microcytic
MCH		27-31 pg	Varies in proportion to MCV Least useful of indices
MCHC		32-36 g/dL	Low MCHC àhypochromic Relatively consistent/pt.
Reticulocyte %
Reticulocyte % with Miller Disk
*Absolute Retic Count (109/L)**
Corrected Retic Count
Reticulocyte Production Index			The maturation time correction factor is based on the patient’s hct and is obtained from a maturation time table
Rules of Three	RBC3 = Hgb ± 0.5 Hgb3 = HCT ± 3%
Neubauer Hemacytometer		Example: 1:20 dilution, 100 WBCs counted in the 4 “W” squares =100x10x20/4=5000 cells per mm3
Absolute WBC	Total WBC x relative count (% from differential)
Corrected WBC			Also used to correct for circulating megakaryocytes

Blood Bank

Platelet Transfusion:

Net gain is post transfusion plt – pretransfusion plt
Number of plts: use 3.0 for plateletpheresis, or #bags x 0.55
Example: Pt. with 10,000 plt count has body surface area of 1.3m2, given 6 units of plts. His count goes up to 50,000 plts after 1 hour.
Corrected Count Increment =
Packed RBCs: Each unit is expected to raise Hgb by 1-1.5 g/dL and HCT by 3-5%