Quick Review Cards for Medical Laboratory Science

Causes and Prevention of False Results

in MDx

Molecular Diagnostics

(MDx) Review 571

CAUSES PREVENTION

False positives
Contamination from other specimens

Contamination with amplicons from previous
target amplification

Environmental contamination

Contamination by testing personnel

False negatives
Inhibitors in sample, e.g., heparin, hemoglobin, lactoferrin

Degradation of nucleic acids during transport/handling

Use of plugged pipet tips & screw cap tubes to minimize sample aerosols

Use of closed tube (real-time) PCR or signal or probe amplification methods;

separate areas for sample prep & amplification with no movement of

equipment or reagents from amplification area to sample prep area; use

of dUTP-UNG system to destroy amplicons from previous amplifications

Use of 10% bleach or alcohol to clean benches, hoods; UV light to decon-

taminate sample prep areas (interferes with DNA replication by breaking

sugar-phosphate backbone)

Use of lab coats, gloves

Proper specimen collection (correct anticoagulant, no hemolysis), use of

internal control or split sample testing (1 aliquot with target added)

Use of transport media, ice, dry ice, or freezing (depending on specimen),

collection tubes designed to stabilize RNA (PAXgene Blood RNA System,

BD Diagnostics), prompt processing or preservation, inhibition of DNases

& RNases

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