Hello Mohamed.

As you said, thick blood smear is used to diagnose malaria. Thin blood smear is used to differentiate the diagnosis - which parasite (plasmodium) is actually responsible for the infection. Different species has different outcome. 

Best regards.

In addition to the answer by lukasz.   if some one is studying drug efficacy on plasmodium the thin smear is helpful 

Thank you for the information Himmat :-). 

In addition, since thick blood smears are not fixed, they enable parasite views outside the host cells and thus concentrated to increase chances of detection during diagnosis. Thin blood smears differentiates the diagnosis since the parasites are viewed within host cells which are often affected differently by different parasite species.

As  Łukasz Frąckowski explains, the thick smear is used to make the diagnosis of malaria as it is a concentration technique. The thin smear keeps the red blood cells intact and as Moses Ngeiywa points out, the infected red blood cells are often affected differently by the different malaria species. Thus, the thin smear can reveal morphological features like Maurer's clefts, Shüffner granulations, polyparasitism (more than one parasite in a red blood cell), marginally positioned parasites,...  Although differentiation is not impossible without these characteristics, they make it a lot easier to differentiate the species involved.

Beside that, thin smears more clearly in pictures than thick and can differentiated between different stages of parasite or species of parasites.

Indeed! Thick = more chance to detect a parasite (more blood) but image is not clear. Thin = less chance to find a parasite (less blood) but much better definition of the image. Thick might be a first screening method, thin a refining one.

The fastest screening for Malaria is QBC method.

Thin blood smears - preferably made from buffycoat fraction of venous blood to upconcentrate few microbes  - are also used to detect piroplasma in RBC, morulae in WBC (Anaplasma, ehrlichia, coxiella), bartonella like organisms.. Micrococci.. And others.

Sometimes spirochetes (my field of interest) may be detected .. For references http://lymerick.net/why-buffycoat.html 

Alan MacDonald has developed Borrelia DNA specific probes that stain Lyme borrelia (Bbss, B garinii, B afzelii) versus Borrelia miyamotoi in different colors.  See http://facebook.com/daninfekt 

Timing of sampling to day one of relapse cycle is important when looking for spirochetes in blood, because they divide and shed granules so day 3 after outbreak it is difficult to find long spirochetes. 

When looking for intracellular microbes like Babesia the best day to look for intracellular ringforms seem to be the day before expected symptom flare up (ringforms in Danish patients with tickborne infections seem to cycle in 4-5 days..  

One more important thing, in addition to what has been said of the value of information above, is the calculating of parasitized RBCs in a patient's blood. One of the criteria to diagnose severe malaria is to look at the RBCs in thin film to count the parasitized cells comparing to non-parasitized ones. And this can't be achieved in thick film as thick film is not fixed with an alcohol and the water in diluted Geimsa stain makes the RBC to haemolyse and subsequently, the parasite stages will be seen without their hosting cells.

True Wahib and % degree of parasitaemia should not be estimated / counted on buffycoat sample either. 

Indeed, the above answers are true.. but worth noting is that speciation  and calculation of parasitaemia can only be achieved through the thin smear.

I would like to point out that parasitaemia can also be determined on a thick smear though. It is then expressed as the number of asexual parasites per µl of blood. For the parasite count in a thick blood film, the number of asexual parasites is expressed per 200 (or 500) leucocytes (simultaneously count asexual parasites and leucocytes). Using the leukocyte concentration, the number of parasites per µl of blood can be calculated as follows:

 Number of asexual parasites counted

------------------------------------------------------  x Leukocytes concentration

      Number of leukocytes counted

Both thick and thin blood smears have their advantages and disadvantages. In case of a blood check up, I would make a thick smear first to assess the general constitution and the potential presence of any foreign pathogen. The thin smear will enable confirmation and quantification. 

Thin blood smears have the advantages to achieve a better optical differention in the morphology of intracellular parasitic forms/stages as (haemogragarines in erythrozytes). The preparation of thick blood films have advantages in detection of intercellular forms as (Trypanosoma, microfilarae).

Low parasitaemia is better detected when a thick smear is made, while species identification is only possible with a thin smear.

Hi

I quite find this an opportunity to ask something about parasite count. from my database, there were various in reporting the parasite count, for example % parasitemia, in relative with white cell count and plus system. May i know which of these methods measure the gametocyte count? is it in relative with white cell count of which an assumed number of WBCs (8,000/ul) is the criterion?

What is the most accurate method to estimate parasitemia of blood parasites? - ResearchGate. Available from: https://www.researchgate.net/post/What_is_the_most_accurate_method_to_estimate_parasitemia_of_blood_parasites [accessed Aug 21, 2016].

The advantages and disadvantages of thick and thin blood smear can also be looked at in terms of economic wise.

Thick smear takes less time to produce result as compared to thin smear. It is also cost effective since no methanol is required a its preparation.

Nevertheless, thin smear specie specific makes treatment effective as compared to thick smear

the advantages of :

1. thick blood film for diagnosis, because take less time and more parasitemae if it do in proper and standard procedure

2. thin blood smear the objective for differentiated between the species e.g. Plasmodium species, take more time in the stain this mean that is less expensive in the staining by 3.0% Gemisa stain

3.the Gemisa stain is the expensive

the disadvantages of:

1. thick blood film cannot identify the e.g. Plasmodium species because of dehemoglobinized of RBCs in thick smear.

2. thin blood film it depend of the thickness of thin smear of the blood film the quality of the smear it depend on the morphology and size of erythrocytes.

There are several malaria parasites and each has specific features.. Though thick film helps you count the parasite but the thin film can help you know the actual parasite causing the illness, making treatment easy..

In simple terms, thin film is for identification of spp