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Laboratory diagnosis of amoebic keratitis: comparison of four diagnostic methods for different types of clinical specimens.

ABSTRACT: Amoebic keratitis causes significant ocular morbidity in contact lens wearers. Current diagnostic methods for amoebic keratitis are insensitive and labor-intensive and have poor turnaround time. We evaluated four laboratory methods for detection of acanthamoebae in clinical specimens. Deidentified, delinked consecutive specimens from patients with suspected amoebic keratitis were assayed for acanthamoebae by direct smear analysis, culture, and PCR using two different primer sets specific for Acanthamoeba ribosomal DNA. The consensus reference standard was considered fulfilled when the results for any two of the four tests were positive, and the outcome measures were sensitivity and specificity. Of 107 specimens assayed over an 18-month period, 20 were positive for acanthamoebae. The sensitivity and specificity of each assay were as follows, respectively: for smear analysis, 55% (95% confidence interval [CI], 33.2 to 76.8%) and 100%; for culture, 73.7% (95% CI, 54.4 to 93.0%) and 100%; for PCR using Nelson primers, 90% (95% CI, 76.9 to 100%) and 90.8% (95% CI, 84.7 to 96.9%); and for PCR using JDP primers, 65% (95% CI, 44.1 to 85.9%) and 100%. Nelson primer PCR demonstrated a single-organism level of analytic sensitivity. The performance characteristics of the assays varied by specimen type, with contact lenses and casings showing the highest rates of detectable acanthamoebae and the highest diagnostic sensitivities for direct smear analysis, culture, and JDP primer PCR, though these results are based on small numbers and should be interpreted cautiously. These findings have important implications for clinicians collecting diagnostic specimens and for diagnostic laboratories, especially in outbreak situations.

SUBMITTER: Boggild AK

PROVIDER: S-EPMC2681827 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Laboratory diagnosis of amoebic keratitis: comparison of four diagnostic methods for different types of clinical specimens.

Boggild Andrea K AK Martin Donald S DS Lee Theresa Yuling TY Yu Billy B Low Donald E DE

Journal of clinical microbiology 20090325 5

Amoebic keratitis causes significant ocular morbidity in contact lens wearers. Current diagnostic methods for amoebic keratitis are insensitive and labor-intensive and have poor turnaround time. We evaluated four laboratory methods for detection of acanthamoebae in clinical specimens. Deidentified, delinked consecutive specimens from patients with suspected amoebic keratitis were assayed for acanthamoebae by direct smear analysis, culture, and PCR using two different primer sets specific for Aca ...[more]

PMID: 19321727

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Project description:ObjectiveTo compare four haemoglobin measurement methods in whole blood donors.BackgroundTo safeguard donors, blood services measure haemoglobin concentration in advance of each donation. NHS Blood and Transplant's (NHSBT) customary method have been capillary gravimetry (copper sulphate), followed by venous spectrophotometry (HemoCue) for donors failing gravimetry. However, NHSBT's customary method results in 10% of donors being inappropriately bled (ie, with haemoglobin values below the regulatory threshold).MethodsWe compared the following four methods in 21 840 blood donors (aged ≥18 years) recruited from 10 NHSBT centres in England, with the Sysmex XN-2000 haematology analyser, the reference standard: (1) NHSBT's customary method; (2) "post donation" approach, that is, estimating current haemoglobin concentration from that measured by a haematology analyser at a donor's most recent prior donation; (3) "portable haemoglobinometry" (using capillary HemoCue); (4) non-invasive spectrometry (using MBR Haemospect or Orsense NMB200). We assessed sensitivity; specificity; proportion who would have been inappropriately bled, or rejected from donation ("deferred") incorrectly; and test preference.ResultsCompared with the reference standard, the methods ranged in test sensitivity from 17.0% (MBR Haemospect) to 79.0% (portable haemoglobinometry) in men, and from 19.0% (MBR Haemospect) to 82.8% (portable haemoglobinometry) in women. For specificity, the methods ranged from 87.2% (MBR Haemospect) to 99.9% (NHSBT's customary method) in men, and from 74.1% (Orsense NMB200) to 99.8% (NHSBT's customary method) in women. The proportion of donors who would have been inappropriately bled ranged from 2.2% in men for portable haemoglobinometry to 18.9% in women for MBR Haemospect. The proportion of donors who would have been deferred incorrectly with haemoglobin concentration above the minimum threshold ranged from 0.1% in men for NHSBT's customary method to 20.3% in women for OrSense. Most donors preferred non-invasive spectrometry.ConclusionIn the largest study reporting head-to-head comparisons of four methods to measure haemoglobin prior to blood donation, our results support replacement of NHSBT's customary method with portable haemoglobinometry.

Project description:ObjectiveThis study compares two methods for clinical diagnosis of childhood pneumonia that aim to estimate rates of underdiagnosis and overdiagnosis of childhood pneumonia by examining the sensitivity of Integrated Management of Childhood Diseases implementation in routine care against lung ultrasound (LUS) diagnosis.SettingWe conducted observations in 83 public health facilities (dispensaries, health centres and district hospitals) in Pwani, Dodoma and Tabora, Tanzania between October and December 2017.MethodsWe used a novel method to estimate rates of underdiagnosis and overdiagnosis of childhood pneumonia by comparing directly observed public provider diagnoses to the results of diagnoses made by trained clinicians using Mindray DP-10 ultrasound machines. We perform multivariate analysis to identify confounding effects and robustness checks to bound the result. We also explore a number of observable characteristics correlated with higher rates of agreement between provider diagnoses and ultrasound diagnoses.ResultsWe observed 93 providers conducting exams on patients aged 2 months-5 years who presented respiratory symptoms or were given a respiratory diagnosis by the provider. Of these 957 patients, 110 were excluded from analysis resulting in a final sample of 847.17.6% of cases identified as pneumonia via LUS examinations in our sample were diagnosed as pneumonia by providers, suggesting that a significant number of pneumonia cases for which care is sought in the public sector go undiagnosed. Provider knowledge of breath counting and years of experience are positively correlated with higher agreement. While clinical examination rates are not statistically correlated with agreement, it is notable that providers conducted a clinical examination on only about one-third of patients in the sample.ConclusionOur results suggest that provider training and knowledge of clinical examination protocols for pneumonia diagnosis are predictive of correct diagnosis of pneumonia and should be further explored in future research as a tool for improving quality of care.

Dataset Information

Laboratory diagnosis of amoebic keratitis: comparison of four diagnostic methods for different types of clinical specimens.

Publications

Laboratory diagnosis of amoebic keratitis: comparison of four diagnostic methods for different types of clinical specimens.

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