Quick Review Cards for Medical Laboratory Science

Specimen Processing

Molecular Diagnostics

(MDx) Review 547

SAMPLE PREPARATION

Blood or bone marrow

Plasma

Tissue

Bacteria/fungi

*Avoid frost-free freezers because of temp variation. Thawed samples should be thoroughly mixed before testing.

Whole blood can be stored at 2°–25°C for 24–48 hr after collection.

Separate WBCs by:

1. Differential lysis in hypotonic buffer or water (RBCs lysed, WBCs precipitated by centrifugation) or


2. Density gradient centrifugation in Ficoll to isolate mononuclears
   WBCs can be stored at –70°C for up to a year*

Remove from RBCs promptly & hold at –20°C or below. *

Fresh or frozen: grind, homogenize, or mince

Embedded: deparaffinize in xylene, rehydrate in ↓concentrations of ethanol

Break cell walls (enzymes, detergents, NaOH, boiling, or glass beads). Enzyme treatment—less damage

to chromosomal DNA. NaOH & boiling yield ssDNA. Not suitable for restriction enzyme analysis. OK for

amplification.