VALIDATING THE NEWTON

Laboratory Trials


The Newton microscope underwent a series of evaluation  trials at the Diagnostic Laboratory of the Liverpool School of Tropical Medicine. Levels of Malaria Parasitaemia on 100 thick film blood smear samples were read on 3 Newton microscopes and Olympus CX31 compound bench binocular microscopes. Equivalence between the Newton and Bench microscope was the primary line of investigation, and after a series of refinements with satisfying comparative results, the Newton microscope was then trailed similarly in a typical African field environment as follows.


Evaluation of the Newton Portable Microscope for the diagnosis of malaria at village level in West Africa


A field trial of the Newton Portable Microscope was carried out in October-November 2012 in conjunction with the Medical Research Council (MRC) Laboratories at Fajara in The Gambia, West Africa. The trial was designed by Mr Malcolm Guy (former Head of the Dagnall Teaching Laboratory, Liverpool School of Tropical Medicine) and performed with the assistance of three local microscopists from the Clinical Haematology Laboratory and Malaria Research Laboratory. Validation picture

TRIAL DESIGN

100 Giemsa-stained thick blood films that had been prepared from local children with suspected malaria infections were assigned to the trial. To ensure no delay in the treatment of an infected child, the trial was instigated only after the slides had been put through the routine diagnostic service at the MRC Laboratories. The trial protocol was approved by the Local Research Ethics Committee.

Slides were examined and graded according to the parasitaemia by Mr Guy using a Leitz compound microscope fitted with a x100 oil immersion lens and x10 eye-piece.

All infected blood films showed the presence of ring stages and trophozoites of Plasmodium falciparum parasites. A small minority of blood films were co-infected with Plasmodium malariae or Plasmodium ovale. No parasites were seen in a proportion of the blood films and these were designated negative.

A simple plus sign system was used as a proxy to describe parasitaemias of varying density, as follows:


- 0 parasites in 100 high-power fields
+ 1-10 parasites in 100 high-power fields
++ 11-100 parasites in 100 high-power fields
+++ 1-10 parasites in every high-power field
++++ 11-100 parasites in every high-power field



Validation image 2

Slides were assigned a numeric code by Mr Guy and read ‘blind’ by the three microscopists on the Leitz microscope. They were re-coded by Mr Guy and re-read ‘blind’ on the Newton microscope fitted with a x100 oil immersion lens and x10 eye-piece. The microscopes used in the trial incorporated the optional x-y mechanical stage and tripod. In all other respects, they were identical to the Newton NM1-1000.

The median score for the three independent readings obtained on the Leitz and Newton microscopes were compared for each of the 100 blood films.

Results

The three microscopists achieved case detections of malaria infections with a sensitivity of 98% (i.e. 2 out of 100 false negative readings) and specificity of 100% (i.e. no false positive readings) using the Newton portable relative to the Leitz microscope. For each of the false negative readings, two of the three microscopists recorded parasites on the Zeiss microscope, versus one of three on the Newton microscope.

The intensity of infection was scored identically on the two microscopes in 78% of cases. In 22% of cases, it was recorded one star-rating lower in intensity on the Newton microscope. Validation pic 3

MRC PORTABLE MICROSCOPE PROJECT

LEITZ BINOCULAR MICROSCOPE VERSUS THE NEWTON PORTABLE
Slide No. Leitz Newton Comments
1 Pos + Neg (V)
3 Pos ++ Pos ++
4 Pos +++ Pos +++
5 Pos +++ Pos +++
6 Pos +++ Pos ++
7 Neg (V) Neg (V)
8 Pos++++ Pos++++
9 Pos+++ Pos+++
10 Pos+++ Pos+++
11 Pos++++ Pos++++
12 Pos++++ Pos++++
13 Neg (V) Neg (V)
14 Pos+++ Pos+++
15 Pos++++ Pos++++
16 Neg (V) Neg (V)
17 Pos+++ Pos+++
18 Pos+++ Pos+++
19 Neg (V) Neg (V)
20 Pos+++ Pos+++
21 Pos+ Pos+ Sexual stages
only
22 Pos++ Pos++
23 Pos+++ Pos+++
24 Pos+++ Pos+++
25 Neg (V) Neg (V)
26 Pos+++ Pos+++
27 Pos+++ Pos+++
28 Pos+ Pos+
29 Pos+++ Pos+++
30 Pos++ Pos++
31 Pos++++ Pos++++
32 Neg (V) Neg (V)
33 Pos+++ Pos++
34 Pos+++ Pos+++
35 Neg (V) Neg (V)

Slide No. Leitz Newton Comments
36 Pos++++ Pos++++
37 Pos++ Pos++
38 Neg (V) Neg (V)
39 Pos+++ Pos+++
40 Neg (V) Neg (V)
41 Pos+++ Pos+++
42 Pos++++ Pos++++
43 Neg (V) Neg (V)
44 Neg (V) Neg (V)
45 Pos++++ Pos++++
46 Pos++++ Pos++++
47 Pos+ Pos+
48 Pos++++ Pos++++
49 Neg (V) Neg (V)
50 Pos++ Pos+
51 Pos++++ Pos++++
52 Pos++++ Pos++++
53 Pos+++ Pos+++
54 Pos+++ Pos+++ P Malariae
seen
55 Pos+++ Pos+++
56 Pos+ Neg (V)
57 Pos+ Pos+
58 Pos+++ Pos+++
59 Pos++++ Pos++++
60 Pos+++ Pos+++
61 Pos++ Pos++
62 Neg (V) Neg (V)
63 Pos++ Pos++
64 Pos+++ Pos+++
65 Pos++ Pos++
66 Pos++++ Pos++++
67 Pos+++ Pos+++
68 Neg (V) Neg (V)
69 Pos+++ Pos+++
70 Pos+++ Pos+++
Slide No. Leitz Newton Comments
71 Neg (V) Neg (V)
72 Pos++++ Pos++++
73 Pos+++ Pos+++
74 Pos+++ Pos+++
75 Neg (V) Neg (V)
76 Pos++ Pos++
77 Pos+++ Pos+++
78 Pos++ Pos++
79 Pos+++ Pos+++
80 Neg (V) Neg (V)
81 Pos++++ Pos++++
82 Pos++ Pos++
83 Neg (V) Neg (V)
84 Pos++++ Pos++++
85 Neg (V) Neg (V)
86 Pos+++ Pos+++
87 Pos+++ Pos+++
88 Pos+++ Pos+++
89 Pos+++ Pos+++
90 Neg (V) Neg (V)
91 Pos++++ Pos++++
92 Pos++ Pos+
93 Pos+++ Pos+++
94 Pos+++ Pos+++ P Malariae
seen
95 Pos++ Pos++
96 Neg (V) Neg (V)
97 Pos+ Pos+
98 Pos+++ Pos+++
99 Pos++ Pos++
100 Pos+++ Pos+++
Validation pic 4