Table 4.

Effect of Methods of DNA Extraction from Paraffin-Embedded Tissue

Extraction method	Number of laboratories (%)	True positives (%)	False positives (%)
Organic	4/17 (24%)	15/21 (71%)	3/21 (14%)*
Inorganic	5/17 (29%)	12/24 (50%)	0/27 (0%)*
Crude lysate	4/17 (24%)	6/13 (46%)	0/16 (0%)*
Not stated	4/17 (24%)	3/7 (43%)	0/4 (0%)
Totals	17/17 (100%)	36/55 (55%)	3/68 (4%)

Fractions reflect total number of tests positive/total number of tests performed by the participating laboratories, on all distributed formalin-fixed paraffin-embedded tissue material (paired and unpaired). The total number of fixed tissue specimens distributed, to laboratories that responded (n = 17), was 221 (13 × 17). True positives, finding a monoclonal IgH gene rearrangement by PCR in B cell lymphomas; false positives, finding a monoclonal IgH gene rearrangement by PCR in T cell lymphomas.

The only significant difference (P = 0.04) was noted here, with a greater frequency of false positives when using organic extraction methods.