7.2.1 Introduction to rapid diagnostic tests (RDTs) for malaria
The national malaria diagnosis policy in Ethiopia is that Health Extension Workers and Practitioners must test anyone suspected of having malaria by using the RDT for malaria. RDTs are now available in all health posts in areas where malaria is a risk and you will receive some practical training in how to use them.
The Ethiopian national guidelines state that malaria treatment at health post level, or referral from the health post to the health centre, should be based on RDT test results, so knowing how to use the RDT properly is a very important part of your job. In this section you will learn how to use the RDTs more effectively. You will also learn about the precautions you have to take to protect yourself and other patients when working with blood.
How RDTs work
RDTs test whether a person with malaria-like symptoms actually has malaria by testing the blood of the patient for chemical substances produced by malaria parasites. Malaria parasites produce proteins called antigens. RDTs detect malaria antigens, so if they are present, the person will test positive. If malaria antigens are not present, the person will test negative.
The reason for using RDTs
RDTs enable you to find out if a fever is really caused by malaria rather than by other illnesses. You can also get information about which malaria parasites may be causing the infection. The information provided by RDTs is important for three main reasons:
- First, being able to tell quickly whether a patient with fever has malaria or not ensures that the patient can receive the correct treatment.
- Second, if a patient does have malaria, knowing which parasite may be involved is important, as some malaria parasites are more dangerous than others and require more urgent treatment.
Can you remember which malaria parasite causes the most serious malaria in Ethiopia?
P. falciparum can kill a person in 24–48 hours, for example by causing cerebral malaria. P. vivax is less likely to cause complications and is rarely fatal.
You will learn about malaria case management with these drugs in Study Session 8.
- Third, falciparum malaria treatment in Ethiopia is based on artemisinin combination therapy (ACT), which is more expensive than older anti-malarial drugs such as chloroquine (CQ) and sulfadoxine-pyrimethamine (SP). Vivax malaria accounts for 40% of the malaria cases in Ethiopia, but it does not need treatment with ACT. By identifying which patients have falciparum malaria, RDTs can save money, as ACTs will then only be given to patients with falciparum malaria.
By using the RDT you will be able to test for malaria parasites in a patient’s blood, and in this way to provide a more accurate diagnosis than a clinical or presumptive diagnosis. RDTs give results in about 15–20 minutes, so a patient with malaria can begin treatment right away. RDTs do not require any expensive or complicated equipment and can be used by you in the patient’s home. You should be able to learn to use RDTs in just a few hours in your practical training programme.
Limitations of RDTs
RDTs are very effective for diagnosing malaria, but there are some things they cannot do.
First, RDTs cannot test how many malaria parasites there are in the blood – they can only test whether parasites are present or absent. In fact, RDTs do not detect actual parasites; they detect parasite antigens, as mentioned above. Some parasite antigens can remain in the blood for at least two weeks after the parasites have been killed by drugs.
What will be the result if an RDT is used on a person within two weeks of taking anti-malarial drugs, and should you trust the result? Explain your answer.
An RDT used within two weeks of drug treatment may still detect parasite antigens and so give a positive result for malaria infection, even if the person no longer has parasites, because the parasites have been killed by the drugs. This is why this positive result cannot be trusted.
Second, RDTs can be damaged by heat and humidity, so the RDT should not be removed from its sealed package before you are ready to use it. If a package has been open for some time before the RDT is used, the RDT may be damaged and can give an invalid (false) result. You should discard this package and use another, unopened, package.
Actions following positive and negative results from RDTs
The national malaria treatment guidelines now recommend the use of parasite-based diagnosis using RDTs for malaria by community health workers for all age groups, except when the RDT is not available due to logistics problems.
- Before using the RDT, ask the patient if he or she has recently taken anti-malaria medication. If the patient has taken a complete course of anti-malaria medication in the last 5–14 days, a positive RDT result may be misleading (see above). It may be necessary to refer the patient to a health centre with a laboratory for further testing using a microscope.
- If fever persists a few days after a negative RDT result and other appropriate management has been applied, you should re-test the patient with another RDT, as RDTs can sometimes miss early malaria infections.
Otherwise:
- If the patient has not recently taken anti-malarial medication and the test result is positive, treat the person for malaria according to national guidelines (see Study Session 8).
- If a patient has fever and the second test result is still negative, refer them to a higher level health centre.
We now explain how to use an RDT, and how to interpret the results.
7.2 Parasitological diagnosis of malaria