ABSTRACT
This study on formalin based combination fixatives was carried out in the Department of Pathology ABUTH Zaria Nigeria a training institution located in the North West region of Nigeria that offers specialist medical services and processes about 3000 to 4000 samples yearly in its pathology laboratory. The study was aimed at identifying a potentially less toxic formalin based combination fixative as compared to the local (10% formol saline-FS) and international (10% Neutral Buffered Formalin-NBF) standards by virtue of reduction of the concentration of formaldehyde in the combinations to a range within the known functional limits of formaldehyde. The combination fixatives were prepared with less concentration of formaldehyde (Group A - A1: 8% Formol saline, A2: 6% Formol saline and A3: 4% Formol saline) and some with phenol as additive inclusive (Group B- B1: 8% Formol saline with 20g phenol crystals, B2: 6% Formol saline with 20g phenol crystals and B3: 4% Formol saline with 20g phenol crystals). Fresh tissues from Sus domestica were procured based on organ system, passed into freshly prepared fixatives and allowed to fix for 24hours. The tissues were then grossed and processed in the laboratory. The slides were stained with the routine stain (Haematoxyline and Eosin - H&E), special stains (PAS & MT) and immunohistochemistry-IHC (EMA & CD23). The screened slides were presented to five pathologists in a single blinded manner for microscopic histomorphologic assessment using modified Allred scoring system. The results showed that the fixative with the best performance was NBF with a percentage overall performance grade of 13.2%, followed by FS with a performance grade of 12.6%, A3 with 12.5%, the phenol containing groups i.e. B1, B2 and B3 with percentage of 12.4% each, then A2 with 12.3% and A1 the lowest grade percentage of 12.1%. These grades were a fair reflection of tissue preservation properties and staining properties of the fixatives. Individual performances based on tissue type, some of the combination fixatives performed better than the standards. The IHC performances in a viii decreasing order are; EMA- B3(6.7%), B2(6.3%), B1(6.3%), NBF(5.9%), FS(5.9%), A1(5.5%), A2(5.1%). CD23- A3(6.7%), B1(6.7%), B3(6.7%), B2(6.3%), NBF(6.3%), FS(6.3%), A1(6.3%), A2(6.3%). For special stains performances in a decreasing order are; PAS- B2(7.5%), FS(6.3%), NBF(5.9%), A1(5.9%), A2(5.9%), B1(5.9%), A3(5.5%), B3(5.5%). MT- FS(7.1%), NBF(6.7%), A1(6.7%), B1(6.7%), A2(6.3%), A3(6.3%), B3(5.9%), B2(5.5%). The overall difference between the best grade and the lowest grade percentage was 1.1% i.e. less than 10% of the responses. The overall result of responses showed 3.67% (less than 10% of responses) graded the performances as suboptimal and poor while 75.63% graded the performances good and 20.70% graded it very good. The results from microscopic assessments done by the pathologists, showed virtually an unremarkable difference in the performances of the combination formalin based fixatives when compared to the local and international standards as evidenced by the hypothesis test (Chi-square and ANOVA) results and p values greater than 0.05, all supported the maintenance of the null hypothesis. Thus, it is recommended that any one of the experimental formalin based combination fixatives can be used as a potentially less toxic suitable substitution to 10% formol saline.