Diagnosis of placental malaria in poorly fixed and processed placental tissue

Abstract

BackgroundPlacental histopathology has been considered the gold standard for diagnosis of malaria during pregnancy. However, in under-resourced areas placental tissue is often improperly fixed and processed; the resulting formalin pigment is difficult to distinguish from malaria pigment. This study examines two alternative diagnostic methods: polymerase chain reaction (PCR) and a novel immunohistochemistry (IHC)-based method using an antibody against histidine-rich protein 2 (HRP2).MethodsPlacental histopathology from 151 pregnant women in Kinshasa was assessed by two blinded microscopists and compared with peripheral blood PCR and IHC for HRP2. The Cohen’s kappa coefficients were calculated to assess the test agreement. The sensitivity and specificity of individual tests were calculated using PCR or IHC as the reference standard as well as latent class analysis (LCA).ResultsPCR and IHC correlated fairly well. The correlation between the two blinded microscopists was poor, as there was widespread formalin pigment. Using LCA, all of the tests had high specificities. The most sensitive test was IHC (67.7 %), with PCR as second-best (56.1 %).ConclusionsPCR and/or IHC are suitable diagnostics when the presence of formalin pigment substantially compromises placental histopathology.

An overview of malaria in pregnancy

“…In research studies, the gold standard for malaria diagnosis has been placental histopathology, but it is not practical in many field sites. 53,54 Using microscopy of placental blood as the referent, the sensitivity of RDTs is 81% (95% CI 55-93) and the specificity is 94% (95% CI 76-99). 31 Molecular techniques, such as polymerase chain reaction (PCR) diagnosis, have increased sensitivity of diagnosis when compared to microscopy of placental blood to 94% (95% CI 86-98), but specificity of 94% (95% CI 86-98).…”

Placental Malaria

“…Despite these instructions, there are some challenges for histologic diagnosis. Due to improper fixation of placental tissue, unbuffered formalin pigment can accumulate and resemble malaria pigment, making it difficult to distinguish them from each other for a correct diagnosis [ 65 ], and fixation with buffered formalin preparation is important for accurate diagnosis by histopathology. Placental impression smear has been proposed as an easier and cheaper method compared with placental histology, and may be useful in settings where histopathology cannot be performed [ 66 ].…”

Rapid Diagnostic Test Performance Assessed Using Latent Class Analysis for the Diagnosis of Plasmodium falciparum Placental Malaria

“…Histopathologic analysis by trained personnel of fixed placental tissue is often considered as the reference standard, 1 but its reliability can be undermined by multiple factors. 3 Other approaches, using placental or peripheral blood, include parasite detection by traditional microscopy, rapid diagnostic tests (RDTs), or polymerase chain reaction (PCR) assays. Compared with histopathology, peripheral blood testing by microscopy 4 or by RDT has been insensitive for placental malaria.…”

“…Similarly, in a prior study in Malawi which used Bayesian LCA models to assess the operating characteristics of microscopy, PCR, and histopathology, the LCA-estimated sensitivity of histopathology was only 50%. 14 Because of this, future studies of placental malaria prevention should incorporate multiple approaches to diag-nosis and test alternate approaches, including enhanced immunohistochemistry, 15,16 large-volume specimen preparation for PCR, 17 or novel nucleic acid detection assays. 18 Our study suggests that peripheral or placental blood RDT testing at delivery can be useful tools for the routine diagnosis of placental malaria for surveillance.…”