Chemistry Rotation Exam

Accuracy

closeness of agreement between the measured value and a true concentration of the analyte

Precision

Agreement among replicate measurements

AMR

Analytical measurement range- range a method can directly measure without dilution, concentration, or other pretreatments

RR

Reportable Range- Range of values that can be reported to include dilutions

Sensitivity

Abillty to assess small variations in concentration of analytes (Also known as how low can we detect our analyte)

Specificity

Ability to determine the concentration of the target analyte in the presence of potentially interfering substances ( also known as are you sure what you see is our analyte)

Control

• Should always include 2+ levels of controls

  • Assayed- controls with stated/expected value

  • Unassayed- Controls with values that are not known expect when assayed by the lab

• Requires > 20 data points from 20- separate runs over no more than 30 days

Imprecision

Change in SD caused by increased variation in values around the mean, due to random analytical error

Inaccuracy

Difference between measured value and actual value, due to systematic error (all samples are affected)

Shift

Abrupt change, could be due to change in lot, maintenance, inaccurate calibration, failure in sampling system

Trend

Gradual change over a period of 6 consecutive days, could be due to deterioration of light, reagents, controls, etc.

1-2s

1 sample exceeds the mean by 2SD ±

• warning flag, don’t need to reject run

1-3s

1 sample exceeds the mean by 3SD ±

• Must reject the run

2-2s

2 consecutive controls exceed the means by 2SD ±

• must be on the same side of the mean

• Must reject run

R-4s

The difference between 2 consecutive controls greater than 4 SD

• Must reject the run

4-1s

4 consecutive controls exceed the mean by 1 SD ± on 1 side of the mean

• must reject the run

10x bar

10 consecutive controls fall on 1 side of the mean

• Must reject the run

KLAAMPI

Hemolysis causes increased

• K+

• LD

• AST

• Ammonia

• Mg

• PO4

• iCal

Serum

Used for special testing or Most therapeutic drugs

Plasma

Used for most chemistry tests

Ice- ammonia, blood gas, whole blood iCals

Grey top

Sodium fluoride: slows glycolysis and inhibits urease

CANNOT use for BUN

Used for Lactic acid testing

EDTA

contains K and chelates Ca

Cannot be used for chemistry

Friedewald Equation

LDL= (Total cholesterol - HDL) - (Triglyceride / 5)

Trigs MUST be <400 mg/dL

CK-MB RI Equation

RI= (CK-MB / Total CK Activity) * 100

if > 2.5% there is likely cardiac damage

if > 5-6% there is definite cardiac damage

Sample Problems

Hemolysis: Cannot test for K or AST

Icterus: Cannot test for Bilirubin (Direct or Total)

Lipemia: Cannot test Triglycerides

Increased Na/Cl and all other analytes decreased

Think line draw/saline contamination

Increased glucose and Decreased K (and all other values)

TPN contamination, call nurse and ask if the patient is on a TPN line, ask for a redraw

Big increase in K/AST

Think hemolysis, look at the sample, ask for a redraw

Large jump in K and steep decrease in Ca

Think EDTA contamination, ask for a redraw due to incorrect collection

Direct ELISA

Looks for Antigen

Patient antigen is on the well

Specific antibody is added with enzyme

Indirect ELISA

Looking for Antibody

Well is coated with Ag

Patient sample is added (Antibodies)

Enzymes is added and measured

Sandwich ELISA

Looking for Antigen

Well is coated with antibodies

Patient sample (Ag) is added to the well

Enzyme-Ab is added to well and measured

Competitive ELISA

Looking for Antigen or Antibody

Ab and Ag are incubated together

Add this mixture to an Ag coated well

Add enzyme Ab to well and measure

What ELISA is this?

Direct ELISA

What ELISA is this?

Indirect ELISA

What ELISA is this?

Sandwich ELISA

What ELISA is this?

Competitive ELISA