- Email: [email protected]
Investigation of bloodstains: false negative results of the benzidine test
Forensic Science International 71 (1995) 85-86
ELSEVIER
Preliminary
Forensic Science International
communication
Investigation of bloodstains: false negative results of the benzidine test F.A. Verdli Pascual*, M.S. Gisbert Grifo Department of Legal Medicine, College of Medicine and Odontology, University of Valencia E.G., 46010 Valencia, Spain
Received 22 February 1994;revision received 8 September 1994;accepted 16 September 1994
Keyworris:
Benzidine Test; Bloodstains; False negatives
Since the discovery of the Benzidine Test, this method has been considered absolutely reliable for the generic diagnosis of bloodstains. The authors reviewed support the existenceof false positive results, as the subtract in the coloration reaction - the peroxidases - may be found in numerous natural products [ 11.There is also general agreementwith the false negative results: a negative result provided by the Benzidine Test indicates that the stain is not blood [2]. Given the strong certainty offered by most works of forensic medicine and criminology, most countries - Spain included - use this technique as a screening method in the investigation of bloodstains: when the result is negative the investigation finishes with the conclusion that ‘the stain was not a bloodstain’. In our Criminology Laboratory, we have observed that there are substances which mixed with blood - provide false negative results in the Benzidine Test. It is well-known that the Benzidine test or oxidase reaction is based on the existence of a blood oxidizing potential which becomesapparent through a change in the colour of the Adler Reactive (benzidine in saturation in acetic acid). Taking this into account, our working hypothesis considers that this potential could be counteracted by the existenceof somesubstanceswith a high reduction power, which may be mixed with the sample investigated. Thus, despite the existence of blood in
l
Corresponding author.
0379-0738/95/$09.50 0 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0379-0738(94)01649-P
86
F.A. Verdti Pam&,
M.S. Gisbert Gr+o / Forensic Sci. ht. 71 (1995) 85-86
Table 1 Blood solution
Samples
l/103
l/IO4
l/l05
0
Lemon juice solution (lemon juice %) 100
90
80
70
60
50
25
0
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
+ +
+ -
+ +
+ +
+ +
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
-
-
+
-
+ -
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s tingerprint)
-
-
-
-
-
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
-
-
-
-
-
-
-
-
-
the sample, it would not becomeapparent, as the reducing substancewould alter the results of the Benzidine Test. We used lemon juice in order to apply our hypothesis. Lemon juice is composed of: water, proteins, fat, sugar, minerals, carotene, vitamin Bl, vitamin B2, nicotinamide, folic acid, vitamin C, malic acid and citric acid. Given its very high reduction potential, we believe ascorbic acid may interfere in the results of the test. This communication shows the results obtained in the first phase of our research. We prepared mixtures of recently extracted blood (vein puncture) and lemon juice (both diluted in distilled water) in different proportions. Then, the Benzidine Test was carried out by using high quality reagents, both fresh and in a test tube, and on supports on which the stain had been dried up. Table 1 shows a summary of the results. The preliminary results show that the use of the Benzidine Test is not sufficiently reliable. The fact that this may affect a criminal investigation (a stain which evidently is blood turns out to be ‘negative’ in the test) has prompted us to write this preliminary communication before carrying on with our research. References [l] [2]
J.A. Gisbert Calabuig, Medicina Lugal y Toxicologia, Salvat, Barcelona, 1991,p. 978. B. Knight, Simpson’s Forensic Medicine, 10th edn., Edward Arnold, London, 1991,p. 59.
ELSEVIER
Preliminary
Forensic Science International
communication
Investigation of bloodstains: false negative results of the benzidine test F.A. Verdli Pascual*, M.S. Gisbert Grifo Department of Legal Medicine, College of Medicine and Odontology, University of Valencia E.G., 46010 Valencia, Spain
Received 22 February 1994;revision received 8 September 1994;accepted 16 September 1994
Keyworris:
Benzidine Test; Bloodstains; False negatives
Since the discovery of the Benzidine Test, this method has been considered absolutely reliable for the generic diagnosis of bloodstains. The authors reviewed support the existenceof false positive results, as the subtract in the coloration reaction - the peroxidases - may be found in numerous natural products [ 11.There is also general agreementwith the false negative results: a negative result provided by the Benzidine Test indicates that the stain is not blood [2]. Given the strong certainty offered by most works of forensic medicine and criminology, most countries - Spain included - use this technique as a screening method in the investigation of bloodstains: when the result is negative the investigation finishes with the conclusion that ‘the stain was not a bloodstain’. In our Criminology Laboratory, we have observed that there are substances which mixed with blood - provide false negative results in the Benzidine Test. It is well-known that the Benzidine test or oxidase reaction is based on the existence of a blood oxidizing potential which becomesapparent through a change in the colour of the Adler Reactive (benzidine in saturation in acetic acid). Taking this into account, our working hypothesis considers that this potential could be counteracted by the existenceof somesubstanceswith a high reduction power, which may be mixed with the sample investigated. Thus, despite the existence of blood in
l
Corresponding author.
0379-0738/95/$09.50 0 1995 Elsevier Science Ireland Ltd. All rights reserved SSDI 0379-0738(94)01649-P
86
F.A. Verdti Pam&,
M.S. Gisbert Gr+o / Forensic Sci. ht. 71 (1995) 85-86
Table 1 Blood solution
Samples
l/103
l/IO4
l/l05
0
Lemon juice solution (lemon juice %) 100
90
80
70
60
50
25
0
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
+ +
+ -
+ +
+ +
+ +
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
-
-
+
-
+ -
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s tingerprint)
-
-
-
-
-
+ +
+ + +
+ + +
Fresh solution Dried stain Paper filter (Taylor’s fingerprint)
-
-
-
-
-
-
-
-
-
the sample, it would not becomeapparent, as the reducing substancewould alter the results of the Benzidine Test. We used lemon juice in order to apply our hypothesis. Lemon juice is composed of: water, proteins, fat, sugar, minerals, carotene, vitamin Bl, vitamin B2, nicotinamide, folic acid, vitamin C, malic acid and citric acid. Given its very high reduction potential, we believe ascorbic acid may interfere in the results of the test. This communication shows the results obtained in the first phase of our research. We prepared mixtures of recently extracted blood (vein puncture) and lemon juice (both diluted in distilled water) in different proportions. Then, the Benzidine Test was carried out by using high quality reagents, both fresh and in a test tube, and on supports on which the stain had been dried up. Table 1 shows a summary of the results. The preliminary results show that the use of the Benzidine Test is not sufficiently reliable. The fact that this may affect a criminal investigation (a stain which evidently is blood turns out to be ‘negative’ in the test) has prompted us to write this preliminary communication before carrying on with our research. References [l] [2]
J.A. Gisbert Calabuig, Medicina Lugal y Toxicologia, Salvat, Barcelona, 1991,p. 978. B. Knight, Simpson’s Forensic Medicine, 10th edn., Edward Arnold, London, 1991,p. 59.