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Table 3 Discrepant TB-bead FM results compared with culture: results of direct ZN and concentrated FM, and blinded re-checking of Magnetic bead results

From: Feasibility of magnetic bead technology for concentration of mycobacteria in sputum prior to fluorescence microscopy

Lab No Direct ZN Conc FM Magnetic bead-FM Magnetic bead re-read*
Magnetic bead false positives (compared to culture)
261 Negative Negative 3+ 3+
206 Negative Negative 1 AFB/40F Negative
099 Negative Negative 1 AFB/40F Negative
259 Negative Negative 3+ 3+
296 Negative Negative 8 AFB/40F Negative
082 Negative 1+ 13 AFB/40F Negative
276 Negative Negative 2 AFB/40F Negative
203 Negative Negative 1 AFB/40F Negative
287 Negative Negative 1 AFB/40F Negative
262 Negative Negative 1 AFB/40F 3+
141 Negative Negative 1 AFB/40F 2 AFB/40F
256 Negative Negative 2 AFB/40F 13 AFB/40F
096 Negative Negative 1 AFB/40F 8 AFB/40F
180 Negative Negative 3 AFB/40F 1 AFB/40F
131 Negative Negative 1 AFB/40F 1 AFB/40F
299 Negative Negative 3+ 1+
302 Negative Negative 2 AFB/40F 3+
211 Negative 1+ 4 AFB/40F Negative
267 Negative Negative 2 AFB/40F 3 AFB/40F
299 Negative Negative 2 AFB/40F 1+
Magnetic bead false negatives compared to culture (with one or more positive result by conc FM or ZN)**
283 5 AFB/40F 2+ Negative 1+
280 2 AFB/40F 2+ Negative 2 AFB/40F
260 1+ 2+ Negative 1+
258 6 AFB/40F 3+ Negative Negative
151 1+ 3+ Negative Negative
084 1+ 1+ Negative Negative
294 Negative 15 AFB/40F Negative Negative
292 Negative 5 AFB/40F Negative 3 AFB/40F
210 Negative 2 AFB/40F Negative Negative
157 Negative 8 AFB/40F Negative Negative
034 Negative 5 AFB/40F Negative Negative
053 Negative 1+ Negative Negative
050 Negative 3+ Negative 3 AFB/40F
011 3 AFB/40F Negative Negative 4 AFB/40F
  1. * Slides were blindly re-checked
  2. **An additional 23 specimens had false negative results by all three microscopy methods and re-checking was not performed.