Table 2.
Theoretical sensitivity of thick and thin blood films of surveyed laboratories (n = 50, MD = 27)
| Guideline/laboratory | Total magnification (ocular × objective) | Thick film | Thin film | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Volume of thick film | Diameter of thick film | Number of fields examined | Theoretical total examined volume | Theoretical limit of detection (based on 2 trophozoites) | Theoretical fields examined | Theoretical total examined volume | Theoretical part of volume examined compared to thick film | ||
| Guideline | * | µL | mm | Number | µL | Trophozoites /µL |
Number | µL | % |
| NVP [9, 12] | 1000 | 6 | 12 | 200 | 0.3 | 7.41 | ND | ||
| BSH [10] | 1000^ | Several drops | – | 200 | ND | ||||
| CDC [11] | 1000^ | Small drop | 17.9** | 100–300 | – | ||||
| WHO [8] | 1000 | 6 | 12 | 100 | 0.1 | 14.29 | ND | ||
| Range | |||||||||
| Minimum | 500 | 6 | 6 | 75 | 0.09 | 1.2 | 40 | 0.002 | 0.8% |
| Maximum | 1250 | 15 | 23.25* | 413 | 1.65 | 21.9 | 600 | 0.056 | 10.3% |
| Mean | NA | 8 | 14 | 207 | 0.47 | 7.4 | 190 | 0.010 | 3.4% |
| Median | NA | 6 | 13 | 200 | 0.31 | 6.5 | 175 | 0.009 | 2.9% |
| Laboratory | |||||||||
| A | 1000 | 6 | 20 | 188 | 0.09 | 21.9 | 188 | 0.009 | 10.3% |
| B | 1000 | – | – | 263 | 0.013 | ||||
| C | 500 | 6 | 15 | 175 | 0.60 | 3.3 | 175 | 0.018 | 2.9% |
| D | 1000 | 6 | 6 | 200 | 1.08 | 1.9 | ND | ||
| E | 1000 | – | – | 338 | 0.017 | ||||
| F | 625 | – | – | 113 | 0.009 | ||||
| G | 500 | – | – | 188 | 0.019 | ||||
| H | 1000 | – | – | 188 | 0.009 | ||||
| I | 1000 | 6 | 13 | 225 | 0.26 | 7.7 | ND | ||
| J | 1000 | – | 10 | 75 | 0.004 | ||||
| K | 1000 | – | – | 275 | 0.014 | ||||
| L | 1250 | 6 | 13 | 338 | 0.31 | 6.5 | 74 | 0.003 | 1.0% |
| M | 1000 | 6 | 15 | 200 | 0.17 | 11.6 | 200 | 0.010 | 5.8% |
| N | 1000 | 6 | 13 | 188 | 0.22 | 9.3 | ND | ||
| O | 1000 | – | – | 263 | 0.013 | ||||
| P | 500 | 6 | 15 | 338 | 1.17 | 1.7 | 563 | 0.056 | 4.8% |
| Q | 500 | 6 | 13 | 225 | 1.04 | 1.9 | – | ||
| R | 500 | – | – | 125 | 0.006 | ||||
| S | 625 | – | – | 413 | 0.009 | ||||
| T | 1000 | 6 | 12 | 200 | 0.27 | 7.4 | ND | ||
| U | 1000 | – | – | 40 | 0.002 | ||||
| V | 1000 | 6 | 11 | 200 | 0.32 | 6.2 | ND | ||
| W | 1000 | 10 | 23.25 | 200 | 0.12 | 16.7 | 75 | 0.004 | 3.1% |
| X | 1000 | 6 | 12 | 200 | 0.27 | 7.4 | ND | ||
| Y | 1000 | – | – | 113 | 0.006 | ||||
| Z | 1000 | 10 | 9 | 413 | 1.65 | 1.2 | 413 | 0.021 | 1.3% |
| AA | 1000 | – | – | 75 | 0.004 | ||||
| AB | 1000 | 6 | – | 49 | 0.002 | ||||
| AC | 1000 | – | 20 | 263 | 0.013 | ||||
| AD | 1000 | – | – | 113 | 0.006 | ||||
| AE | 1000 | – | – | 263 | 0.013 | ||||
| AF | 1000 | 6 | 12 | 200 | 0.27 | 7.4 | – | ||
| AG | 1000 | – | 15 | 49 | 0.002 | ||||
| AH | 1000 | – | – | 263 | 0.013 | ||||
| AI | 1000 | 15 | 14 | 135 | 0.33 | 6.0 | 135 | 0.007 | 2.0% |
| AJ | 1000 | – | – | 338 | 0.017 | ||||
| AK | 1000 | – | – | 175 | 0.009 | ||||
| AL | 1000 | – | – | 74 | 0.004 | ||||
| AM | 1000 | – | – | 200 | 0.010 | ||||
| AN | 1000 | 6 | 12 | 113 | 0.15 | 13.2 | ND | ||
| AO | 1000 | 6 | 10 | 200 | 0.39 | 5.1 | 200 | 0.010 | 2.6% |
| AP | 1000 | 6 | – | 75 | 0.004 | ||||
| AQ | 1000 | 6 | – | 600 | 0.030 | ||||
| AR | 1000 | – | – | 75 | 0.004 | ||||
| AS | 625 | 15 | 16 | 75 | 0.45 | 4.4 | ND | ||
| AT | 1000 | – | – | 188 | 0.009 | ||||
| AU | 1000 | 15 | – | 74 | 0.004 | ||||
| AV | 1000 | 6 | 10 | 225 | 0.44 | 4.6 | 74 | 0.004 | 0.8% |
| AW | 1000 | 12 | 15 | 113 | 0.19 | 10.3 | 113 | 0.006 | 2.9% |
| AX | 1000 | – | – | 113 | 0.006 | ||||
–: missing data; .: no calculation possible due to missing data; ND: not determined for the detection of parasites; NA: not applicable
*The size of 1 euro coin
**The size of a US dollar dime
^1000× magnification and FN 18 of the ocular is assumed, based on the use of a 100× objective