TDR/EMRO FINAL REPORT SUMMARY 1995–2000
Malaria: Laboratory diagnosis Abstract
Decisive assessment of diagnostic
The present study was conducted in 8
staining methods of malaria in eight laboratories in Khartoum State during the
public and private laboratories, period September 1995–December 1996, to
Khartoum area evaluate the accuracy of diagnosis and staining
of malaria in selected public and private
Sudan: Khartoum State
laboratories. All patients referred for fever were
examined. Two slides were taken for each
September 1995–December 1996 patient; one for routine blood film and the other
processed using standard Giemsa stain as a
Small Grants Scheme (SGS) 1995 no 12 reference technique in the National Health
Laboratories. The standard Giemsa technique
showed that 13% of cases presenting with
fever were tested positive for malaria.
P. falciparum was the main species identified
PRINCIPAL INVESTIGATOR (96.2%), and the remaining proportion was
Ms Samia Mamoun Ibrahim P.vivax .
Department of Parasitology, The sensitivity of the light microscope ranged
National Health Laboratories, from 50% in some laboratories up to 75% in
P.O.Box 2371, Khartoum 11111
others. Similarly, its specificity ranged from
Fax: 002 249 11 781845 52.63% up to 95.65%. These results indicate
e-mail: email@example.com that the performance of the field laboratories
was strikingly variable.
The low sensitivity of the light microscope in
some laboratories reveals that many positive
cases will remain undiagnosed. And the low
CONCLUSIONS AND IMPLICATIONS OF THE STUDY specificity in other laboratories reveals that a
considerable per cent of individuals will be
q The results of the different laboratories were strikingly wrongly diagnosed as having malaria.
variable, sometimes unreliable and, in many instances, In 4 laboratories, the results were absolutely
irrelevant. Suboptimal performance was attributed to the unreliable. Suboptimal performance was
high workload and poor supervision. attributed to the high workload and poor
q Laboratory errors in addition to the malfunctioning of This study emphasizes the need to direct the
the available light microscopes indicate that diagnosis of limited available health care resources towards
malaria in countries with limited resources is more reliable the provision of laboratory facilities, continuing
with Giemsa rather than with Field stain. It is therefore medical and technical education of health
recommended to abstain the use of Field stain for malaria
professionals as well as organizing training
workshops for the technical personnel.
q This study emphasizes the need to direct the limited
health care resources towards the provision of laboratory
facilities, continuing medical and technical education of
health professionals, and tight supervision and training of
the technical personnel. The need for a quality assurance
system is also emphasized.
Continued on page 2
Applied Field Research (AFR) 1
continued from page 1
Background The prevalence of malaria in Sudan Individual technicians do not follow the steps of
remains constant high due to the presence of the staining technique. They never adjust their
favourable environmental conditions and time according to the diminishing concentration
progressive expansion and cultivation of of stain throughout the day. The same amount of
agricultural land. As light microscopy is the most diluted stain might be used for several days
reliable diagnostic method of parasitaemia (1), without filtration. In other instances, they use
prompt diagnosis of malaria cases is dependent water—which might be contaminated—instead
upon the accuracy of laboratory investigations, of buffer. As a result, the chromatin of the
provided that results can be rapidly communicated malaria parasites is seldom differentiated and
to the health care providers. The aim of this study the microscopic field contains a lot of micro-
was to evaluate the accuracy of diagnosis and organisms and dirt. As a rule, 100 microscopic
staining techniques of malaria in public and private fields of each slide should be examined. This is
laboratories. rarely done. Usually, after coming across the
Methods: Eight public and private laboratories first few parasites the technicians declare the
slide positive and decide which species is
were selected from the 3 administrative Khartoum
involved. On the other hand, if the slide is too
bad to be examined, because the blood has
The personnel of these laboratories were briefed
been washed or otherwise destroyed and no
about the study. All patients referred for fever
parasites are in sight, the slide is always
were examined. Two slides were taken for each
declared negative. These previously mentioned
patient; one for routine blood film (Field stain) (2)
laboratory errors, in addition to the
and the other processed using standard Giemsa
malfunctioning of the available light
stain as a reference technique (reference stain) in
microscopes, indicate that diagnosis of malaria
the National Health Laboratories (NHL).
can be determined with Giemsa rather than with
A patient was considered negative if no parasites
were seen in 100 microscopic fields of each slide.
After examination and identification of the parasite Recommendations
species and stage, the parasite density was
The results of this study indicate the necessity
computed. Slides were cross checked by three
of abstaining from the use of Field stain for
investigators. Field stain results obtained by light
microscopy were then compared to the results of
This study also emphasizes the need to direct
the reference stain obtained from the NHL.
the limited health care resources available
Statistical analysis: validity of diagnosing malaria
towards the provision of laboratory facilities such
with light microscope was computed using the
as equipment and regular supply of reagents.
SPSS statistical package.
Results Continuing medical and technical education of
health professionals together with training and
The standard Giemsa technique showed that 13%
tight supervision of the technical personnel is
of cases presenting with fever tested positive for
warranted. The importance of establishing a
malaria. P. falciparum was the main species
quality assurance system is also emphasized.
identified (96.2%), and the remaining proportion
was P. vivax.
The sensitivity of the light microscope ranged from
1.Omer, A.H.S. Species prevalence of malaria in
50% in some laboratories up to 75% in others.
Northern and Southern Sudan and control by
Similarly, its specificity ranged from 52.63% up to
mass chemoprophylaxis. Am. J. Trop. Med. Hyg
95.65%. These results indicate that the
performance of the field laboratories was strikingly
variable. The low sensitivity of the light
2.Shute, G. T. (1988) . The microscopic
microscope in some laboratories reveals that
diagnosis of malaria .p781–814. In Malaria,
many positive cases will remain undiagnosed
principles and practice of malariology (ed.
(high frequency of false negative cases). And the
low specificity reveals that a considerable per cent
Livingstone Edinburgh London Melbourne and
of individuals will be wrongly diagnosed as having
malaria (false positive).
In four laboratories, the results were absolutely
unreliable. Suboptimal performance was attributed
to the high workload and poor supervision.
Applied Field Research (AFR) 2