Clinical Chemistry Lab Practical General Concepts

Define a Blank

all components except analyte as it accounts for sample color

Define a Reagent Blank

all reagents but no sample, it accounts for abs due to reagents

Define spectrophotometer Light source

beam of UV light for the spectrum analysis

Define spectrophotometer Monochromator

separates white light into wavelengths with a prism and selects the wavelength band needed

Define spectrophotometer Cuvette

hold sample liquid

Define spectrophotometer Detector

converts the light that passes through the sample into an electrical signal, measuring its intensity

Define spectrophotometer Readout device

converts the detector’s electrical signal into abs number

Define spectrophotometer Optimal wavelength

wavelength where analyte has maximum abs (lambda max)

Describe the relationship b/w absorbance and percent transmittance

Inverse relationship= A = 2 -log(%T)

State Sources of error of interference that can occur when using a spectrophotometer

Lipemia (excess fat/ white plasma), Hemolysis (RBC breakdown/ red plasma), Icterus (hyperbilirubinemia/ yellow-brown-green plasma), stray light, bubbles, dirty cuvettes

Interpret the results of the graph and standard curve to indicate the relationship b/w absorbance and concentration

Absorbance increases with concentration, linear graph ( straight line). Steep slope = more absorbance per concentration

Define the analytical measurement range (AMR)

Range measurable directly without dilution

Define the clinical reportable range (CLR)

Range of value reliably reported to clinicians after dilution

Define Linearity

range where instrument response is proportional to concentration

State what to do with samples above the linear range

dilute it to bring the analyte into measurable range for accurate results

Define Solute

substance dissolved

Define Solvent

substance doing the dissolving

Define Mass percentage

Proportion of a component relative to the total solution expressed in %

Define Molarity

Moles of a solute per liter of solution, volume changes with temperature, used for reaction rates and standard curves

Define Molality

Moles of solute per kilograms of solvent, temp-independent helpful with temps like freezing

Define Normality

Equivalents of Solute per liter of solution, depends on reaction time, 1 mole DOESN’T = 1 equivalent (Ex. Acid-base for H+ number & redox for electrons transferred)

Equation for Mol Solute

= (solute grams / gram molecular weight of solute)

Define mole fraction

Ratio of moles of one component to total moles in solution, ratio no unit, unaffected by temp or pressure

Equation for mole fraction

X=(moles of component) / (total moles of all components)

Equation for W/v%

% = (grams of solute / 100.0 mL of solutions) x 100

Equation for v/v%

(mL solute / 100.0 mL solution) x 100

Equation for W/W%

(gram solute / 100.0g solution) x 100

Equation for Molarity

M= moles of solute / Liters of solution

Equation for Molality

m= (moles of solute) / (kg of solvent)

Equation for Normality

= (Grams equivalent of solute) / (liters of solution)

Equation for Dilution Factor

DF= total volume / Aliquot Volume

How to make a 1:10 dilution

1 part sample + 9 parts diluent

Define Westguard rules

A set of rules to detect analytical errors in QC (1 2s, 2 2s, R 4s, etc)

Define Westguard rules 1 2s

one control exceeds +/- 2 SD; warning rule

Define Westguard rules 2 2s

Two consecutive controls exceed +/- 2 SD on same side; reject run

Define Westguard rules R 4s

difference of 4 SD between controls; indicates random error

Define Westguard rules 4 1s

Four consecutive controls exceed +/- 1 SD on same side; indicates systematic error

Define Westguard rules 10X

Ten consecutive results on the same side of the mean; indicates systematic error

Define sensitivity

ability of a test to correctly ID people who have the disease

Sensitivity Equation

= [(TP) / (TP + FN) X 100]

Sensitivity false negative %

5

Sensitivity % positive

95

What test is Sensitivity used for

Screening test

Define Specificity

ability of a test to ID people who do not have the disease

Specificity Equation

= [(TN) / (TN + FP) X 100]

Specificity false negative %

2

Specificity % positive

98

What test is Specificity used for

confirmatory tests

Define Positive predictive value

Probability that a person with a positive test has the disease

Positive predictive value Equation

= [(TP) / (TP + FP) X 100]

Positive predictive value false negative %

20

Positive predictive value %

80

Positive predictive value means the ____ disease a population is the _____ the PPV is

more, higher

Define Negative predictive value

Probability that a person with a negative test does not have the disease

Negative predictive value Equation

= [(TN) / (TN + FN) X 100]

Negative predictive value false negative %

1

Negative predictive value %

99

Negative predictive value depends on disease_____

prevalance

Why would you want high sensitivity on a screening test

so you don't miss the disease

Why would you want high specificity on confirmatory tests

to avoid false positives

Interpreting patient results: Positive results means PPV OR NPV

PPV reasoning

Interpreting patient results: Negative results means PPV OR NPV

NPV reasoning

Define: Accuracy

Degree that a test result is aligned with the true value of an analyte, how close to the true value the measurement it

Define: Precision

Degree of reproducibility/consistency. How close the measurements are to each other.

Define: Linearity

The results are directly proportional to analyte concentration

Define: Quality Control

Monitoring performance by testing controls that have known value ranges.

Define: Calibrator / calibration

Adjusting an instrument or analytical system by using known concentrations.

Define: Standard (reference material)

Substance that has a known value and is used as a basis for calibration and concentration calculations

Define: Matrix (specimen or reference material)

Entire chemical/physical environment of a specimen or reference material.

Equation of Coefficient of Veriation

CV% = (SD/mean) X 100

Equation for general Concentration

C1V1=C2V2

Gram equivalent weight of solute

= (gram molecular weight of solute / valence)

Grams equivalents of solute

= (solute grams / grams equivalent weight of solute)

Anion Gap (mmol/L) W/ K

= (Na) + (K) - (CL) + (HCO3-)

Anion Gap (mmol/L) W/O K

= (Na) - (CL) + (HCO3-)

Calculated Osmolality (mOsm/kg)

= 1.86 (Na value) + (glucose value / 18) + (BUN value / 2.8)

Osmolal gap (mOsm/kg)

= (measured osmolality) - (calculated osmolality)

Unconjugated (mg/dL)

= (total bilirubin) - (Conjugated)

Conjugated (mg/dL)

= (total bilirubin) - (Unconjugated)

Creatinine Clearance Uncorrected (mL/min)

= (Ucr mg/dL X Vcr mL/24 hours) / (Pcr mg/dL X 1440 min/24 hours)

Creatinine Clearance Corrected (mL/min)

= [(Ucr mg/dL X Vcr mL/24 hours) / (Pcr mg/dL X 1440 min/24 Hours)] X (!.73/A)