Laboratory Equation Guide

SI Units: The International System of Units is a system devised around the convenience of the number ten. It is the worlds most widely used system of measurement in science.

Definitionsandabbreviations

Temperature

SI Standard units are Kelvin (K)

Celsius = K-273

Kelvin = Celsius+273

Temperature Conversions

Celsius = 5/9 (F – 32)

Fahrenheit = (9/5 x C) + 32

Solution

A solution is a homogenous mixture of two or more substances. A solute is a substance that is small part of a solution. A solvent is a substance that constitutes a large portion of a solution. Solubility refers to the solutes ability to dissolve in the solvent.

Dilutions 

A dilution is when the solute or substance of interest is combined with an appropriate volume of solvent to achieve a desired concentration. The dilution factor is the resulting total number of unit volumes in which the solute was dissolved.

For example: Dissolving one part solute into 3 parts solvent. Total dilution is 1:4. The dilution factor is 4 because there are four total parts of unit volumes.

(C1)(V1)=(C2)(V2) is used when making fixed volumes of specific concentrations.

Percent solutions refer to parts per hundred. They can either be percent by volume (% (v/v)) or percent by mass (% (m/m)).

Percent by Volume (% (v/v)) = (Volume of solute/Volume of solution) x 100

Percent by Mass (% (m/m)) = (Mass of solute/Mass of solution) x 100

Molarity is a unit of concentration equal to the number of moles of solute in one liter of solution.

Molarity (M) = Moles of solute/Liters of solution

Density is the ratio between the mass and volume of a material.

Density = Mass/Volume

Clinical Validity

Specificity: The frequency of a negative test when no disease is present.

Specificity = (True negatives/True negatives+False positives) x 100

Sensitivity: The frequency of a positive test when disease is present.

Sensitivity = (True positives/True positives+False negatives) x 100

Chemistry

Calculated plasma osmolality = 2[Na+] + Glucose/18 + BUN/2.8

Osmolar Gap: Difference between the measured and calculated osmolality.

Friedman Formula:

LDL = Total cholesterol – HDL – VLDL

Triglycerides = (Total cholesterol – HDL – LDL) x 5

Precaution: The Friedman formula is only reliable for triglyceride levels less than 400 mg/dL.

Bilirubin

Total Bilirubin = Conjugated bilirubin + Unconjugated bilirubin

Conjugated Bilirubin = Total bilirubin – Unconjugated bilirubin

Unconjugated bilirubin = Total bilirubin – Conjugated bilirubin

Creatinine Clearance

Cockcroft-Gault Equation

Creatinine Clearance = Male (1.0), Female (0.85) x (140-age) x (Serum Creatinine) x (Weight/72).

Hematology

Hematocrit: The percentage of blood that is represented by packed red cells.

Hematocrit (%) = Hemoglobin x 3

MCV: Mean cell volume refers to the average size of the red cell population within the sample.

MCV = (Hematocrit (%) x 10)/RBC (x10^12/L)

MCH: Mean cell hemoglobin refers to the average weight of hemoglobin within the red cell population.

MCH = (Hgb x 10)/RBC (x10^12/L)

MCHC: Mean cell hemoglobin concentration refers to the average concentration of hemoglobin within the red cells constituting the sample.

MCHC: (Hgb x 100)/Hematocrit (%)

Corrected WBC: Nucleated RBCs are counted as white blood cells regardless of which method is utilized. For this reason when a differential is performed and there is presence of NRBCs a corrected WBC must be calculated. The number of NRBCs per 100 leukocytes is recorded during the differential leukocyte count when performing a blood smear examination. This number is then used;

Corrected WBC = (WBC x 100)/(NRBC + 100)

 

 

 

 

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