TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: LCMAL    
Malaria, Molecular Detection, PCR, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Detection of Plasmodium DNA and identification of the infecting species

 

An adjunct to conventional microscopy of Giemsa-stained films, particularly in cases of low percent parasitemia or suboptimal parasite morphology

 

Detection and confirmatory identification of Plasmodium species: P falciparum, P vivax, P ovale, P malariae, and P knowlesi

 

This test should not be used to screen asymptomatic patients.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

See Malaria Laboratory Testing Algorithm in Special Instructions.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Malaria is a mosquito-transmitted disease caused by apicomplexan parasites in the genus Plasmodium. It is an important cause of morbidity and mortality worldwide, with the World Health Organization (WHO) estimating 219 million cases and 435,000 malaria-related deaths in 2017. Malaria disproportionately affects individuals living in Africa (90% of cases), with individuals living in southeast Asia and the eastern Mediterranean regions next most affected. Malaria is also encountered outside of endemic regions such as the United States, usually in returning travelers.

 

Malaria is caused primarily by 4 species of the protozoa Plasmodium: P falciparum, P vivax, P malariae, and P ovale. A fifth Plasmodium species, P knowlesi, is a simian parasite that may be an important source of human infection in some regions of Southeast Asia. Differentiating P falciparum and P knowlesi from other species is important since both can cause life-threatening infections. In addition, P falciparum is typically resistant to many commonly used antimalarial agents such as chloroquine.

 

Microscopy of Giemsa-stained thick and thin blood films is the standard laboratory method for diagnosis and differentiation of malaria parasites. Under optimal conditions, the sensitivity of the thick film microscopy is estimated to be 10 to 30 parasites per microliter of blood. However, microscopic diagnosis requires considerable expertise and may be insensitive or nonspecific when inadequate training and facilities are available. Furthermore, prolonged exposure to EDTA, transportation conditions, and prior use of antimalarial drugs may alter parasite morphology and negatively impact the ability to perform species identification by microscopy. Finally, Babesia parasites have a similar appearance to P falciparum ring forms (early trophozoites) on peripheral blood films, resulting in potential diagnostic confusion.

 

PCR is an alternative method of malaria diagnosis that allows for sensitive and specific detection of Plasmodium species DNA from peripheral blood. PCR may be more sensitive than conventional microscopy in very low parasitemias, and is more specific for species identification. It may be particularly useful when subjective microscopy does not permit certain identification of the species present. Malaria PCR can be used in conjunction with a traditional blood film or Babesia PCR when the clinical or morphologic differential includes both babesiosis and malaria. Examination of the thin film also allows for calculation of percent parasitemia, which can be used to predict prognosis and monitor response to treatment. This test does not include blood smear examination or calculation of parasitemia.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Interpretation Provides information to assist in interpretation of the test results

A positive result indicates the presence of Plasmodium nucleic acid and melting curve analysis indicates the infecting species.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Malaria is potentially a life-threatening disease, and it is imperative to test for parasites as rapidly as possible. Therefore, this test is for confirmation only except for clients in the immediate Rochester, Minnesota area who can provide rapid delivery of specimens to Mayo Clinic Laboratories.

 

Assay may be negative in very low parasitemias.

 

Species of Plasmodium present in mixed infections may not be clearly delineated.

 

In some instances, the closely related species, P ovale and P vivax, cannot be differentiated from one another by this test. In this instance, results will be reported as "Plasmodium vivax/Plasmodium ovale." These 2 species have similar prognosis and treatment, and can often be distinguished based on patient travel history.

 

This is a qualitative test only. If calculation of percent parasitemia is desired, order LMALP / Malaria PCR with Parasitemia Reflex, Varies.

 

This assay does not distinguish between residual nucleic acid (which may persist after adequate treatment) and viable intact parasites. It also does not distinguish between gametocytes (nonpathogenic forms that may be present in resolving infections) and virulent trophozoites.

 

Although the reference range is considered "negative" for individuals living in nonendemic areas, this assay may detect low-grade asymptomatic parasitemia from individuals exposed to malaria-endemic areas. However, this assay is designed to detect only Plasmodium species of clinical significance and is to be used for patients with a clinical history and symptoms consistent with malaria. This test should not be used to screen asymptomatic patients.

 

This PCR assay does not detect other parasites that may be present in the blood and have similar disease presentations including Babesia and Trypanosoma species.

Supportive Data

The following supports the use of this assay for clinical testing.

 

Accuracy/Diagnostic Sensitivity and Specificity:

160 clinical whole blood specimens were evaluated for the presence of Plasmodium species DNA or the 18S rRNA gene using this real-time PCR assay. The assay detects and differentiates DNA of P falciparum, P vivax, P ovale, P malariae, and P knowlesi. The results were compared to results of microscopy, a nested PCR method and sequencing. The specimens comprised 48 negative and 108 positive specimens (32 P falciparum, 8 P malariae, 20 P ovale, 45 P vivax, 2 unable to speciate by morphology, and 1 mixed infection of P vivax/falciparum). The sensitivity and specificity of the real-time Plasmodium assay compared to microscopy, nested PCR and sequencing was 99% and 94% respectively, with all species determinations by the PCR assay matching the original result. No P knowlesi clinical specimens were available so spiking studies were performed. 30 EDTA-anticoagulated blood specimens received in the laboratory for unrelated testing were spiked with P knowlesi plasmid near the limit of detection (50-100 targets per microliter) and tested in a blinded fashion with negative blood specimens. 100% concordance was achieved in the spiking studies.

 

Analytical Sensitivity/Limit of Detection:

The lower limit of detection (LoD) of this assay is 10 to 50 DNA target copies per microliter in whole blood.

 

Analytical Specificity:

No PCR signal was obtained from extracts of 31 other bacterial, viral, rickettsial, and parasitic isolates that could be found in whole blood and cause similar symptoms, including Babesia, Borrelia, Anaplasma, and Ehrlichia species.

 

Precision:

Interassay precision was 100% and the intra-assay precision was 100%. 

 

Reportable Range:

This is a qualitative assay and the results are reported as either negative or positive for the targeted Plasmodium species.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Mathison BA, Pritt BS: Update on Malaria Diagnostics and Test Utilization. J Clin Microbiol. 2017 Jul;55(7):2009-2017

2. Swan H, Sloan L, Muyombwe A, et al: Evaluation of a real-time polymerase chain reaction assay for the diagnosis of malaria in patients from Thailand. Am J Trop Med Hyg 2005 Nov;73(5):850-854

3. World Health Organization Malaria Page: www.who.int/topics/malaria/en/

4. Cox-Singh J, Davis T, Lee K, et al: Plasmodium knowlesi malaria in humans is widely distributed and potentially life-threatening. Clin Infect Dis 2008 January 15;46(2):165-171

Special Instructions Library of PDFs including pertinent information and forms related to the test