The number of amastigotes in a needle aspirate of the spleen can be counted to give an indication of the parasite load in a patient with visceral leishmaniasis. The count is converted to a grade (also called a parasite density score), with each grade roughly showing a 10-fold increase in the number of parasites. This can be used on initial diagnosis and later to assess response to therapy.
Sample:
(1) A smear is made from a needle aspirate of the spleen.
(2) A variety of stains may be used on the smear, usually a Wright-Giemsa stain.
Microscopic examination:
(1) magnification 1,000 times (10x ocular, 100x objective with oil immersion)
(2) count up to 1,000 microscopic fields
average parasite density
Grade
0 in 1,000 microscopic fields
0
1-10 parasites in 1,000 fields
1+
1-10 parasites in 100 fields
2+
1-10 parasites in 10 fields
3+
1-10 parasites per field
4+
10-100 parasites per field
5+
> 100 parasites per field
6+
Comparison with culture:
(1) A small number of organisms may be missed on smear yet grow on culture.
(2) An organism seen on smear may not be viable in culture.
(3) In general, culture is more sensitive than smear examination.
To read more or access our algorithms and calculators, please log in or register.
