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

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

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

* Slides were blindly re-checked
**An additional 23 specimens had false negative results by all three microscopy methods and re-checking was not performed.

ISSN: 1471-2334