STEP 2: Add two drops of the Guaiac solution.
STEP 3: Add two drops of glacial acetic acid.
STEP 4: Add two drops of three percent hydrogen peroxide.
(3)
Interpretation.
(a) Immediate dark blue color indicates a 4+ reaction.
(b) Dark blue color after 30 seconds indicates a 3+ reaction.
(c)
A blue color within three minutes indicates a 2+ reaction.
(d) A slow light blue color indicates a 1+ reaction.
(e) A negative reaction is indicated by the absence of any blue color
within five minutes.
c. Other Tests for Occult Blood. There are various other products in the market
that have satisfactory results.
2-18. PRESERVATION
Whenever specimens cannot be examined immediately after collection, a portion
or the whole sample can be preserved for later examination. This procedure maintains
parasites in their existing morphological form and structure. There is no perfect fixative
and the method of preservation is usually determined by the particular organism
suspected.
a. Formalin. While protozoan trophozoites are destroyed by formalin, cysts, ova,
and larvae are well preserved. The stool specimens should be preserved within one hour
after collection. A five percent formalin is used for protozoan cysts, for ova of
Hymenolepis species, and for larvae. The 10 percent solution is used for the other
organisms.
(1)
Reagents.
Neutral Buffered Formalin
10%
5%
Formaldehyde ................................................ 10.00 ml ....... 5.00 ml
Distilled water................................................. 90.00 ml ....... 95.00 ml
Sodium phosphate monobasic ....................... 0.40 gm ........ 0.40 gm
Sodium phosphate, dibasic, anhydrous ......... 0.65 gm ........ 0.65 gm
Carefully mix the reagents and swirl vigorously. Store in an aspirator
bottle or in a one liter glass-stoppered bottle.
MD0841
2-35