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Análisis capilar

El análisis capilar puede referirse al análisis químico de una muestra de cabello , pero también puede aludir al análisis o comparación microscópica. El análisis químico del cab...

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El análisis capilar puede referirse al análisis químico de una muestra de cabello , pero también puede aludir al análisis o comparación microscópica. El análisis químico del cabello puede considerarse con fines retrospectivos cuando ya no se espera que la sangre y la orina contengan un contaminante específico, generalmente tres meses o menos después.

Su uso más extendido se da en los campos de la toxicología forense y la toxicología ambiental . Se puede utilizar para detectar la presencia de ciertas drogas en el organismo de una persona, por ejemplo, durante un examen médico previo a la contratación. [ 1 ] [ 2 ] Diversas disciplinas de la medicina alternativa también emplean análisis capilares para la toxicología ambiental, pero estos usos son controvertidos, están en constante evolución y no están estandarizados.

El análisis microscópico del cabello se ha utilizado tradicionalmente en la ciencia forense, y va más allá de la simple comparación del color. Los analistas examinan diversas características del cabello bajo el microscopio, comparando generalmente cabellos de la escena del crimen con cabellos de un sospechoso. Sin embargo, las pruebas de ADN han desacreditado el análisis microscópico del cabello. El análisis de ADN ha demostrado que muchas supuestas coincidencias de cabello eran, de hecho, erróneas, incluso aquellas realizadas por quienes se consideraban expertos en la materia. Esto llevó a la anulación de muchas condenas basadas en el análisis del cabello. Desde 2012, el Departamento de Justicia de los Estados Unidos ha llevado a cabo un estudio de casos en los que sus agentes prestaron testimonio basado en el análisis del cabello, y descubrió que una alta proporción de dicho testimonio no se ajustaba al estado actual de la ciencia del análisis del cabello.

Biología del cabello

Hair consists of various characteristics that can be of use in a forensic examination and analysis. To the core, hair is composed of keratin, water, minerals, and lipids.[3] Hair consist of two distinctions parts, the hair shaft and the hair root.[4] The shaft is composed of 3 layers, first being the medulla which is the inner core (if present), the second being the cortex which is the middle layer composed of multiple cells, and then lastly the cuticle which is the outer layer.[4] The hair root is the bulbous portion of the hair shaft that resides in the hair follicle with the surrounding cells in the hair follicle that allow for production of hair and its growth.[4] There are three phases of hair growth; anagen, catagen and telogen. In the anagen phase, the hair root actively creates the hair shaft.[4] In the catagen and telogen phases, it regresses and gets ready for the following cycle.[3][4] As hair shedding is a natural process, hairs tend to be found in the anagen phase when collected for analysis rather than the regression phase .[3] This can cause issues in analysis as the follicular tag which is located on the hair follicle must be present to be able to analyze it with DNA analysis.[4] If no follicular tag is present, the hair is sent for mitochondrial DNA (mt-DNA), as this is the only way to truly identify there source of hair. In theory, all human hairs are suitable sources for mitochondrial DNA.

In forensic toxicology

Chemical hair analysis is used for the detection of many therapeutic drugs and recreational drugs, including cocaine, heroin, benzodiazepines and amphetamines.[5][6] Hair analysis is less invasive than a blood test, if not quite as universally applicable. In this context, it has been reliably used to determine compliance with therapeutic drug regimes or to check the accuracy of a witness statement that an illicit drug has not been taken. Hair testing is an increasingly common method of assessment in substance misuse, particularly in legal proceedings, or in any situation where a subject may have decided not to tell the entire truth about his or her substance-using history. Post-mortem hair sample analysis can also be performed, to allow for determination of long-term drug use or poisoning.[7] It is also used by employers, who test their employees.

Hair analysis has the virtue of showing a 'history' of drug use due to hair's slow growth. Urine analysis might detect drugs taken in the past 2–3 days; hair analysis can sometimes detect use as far as 90 days, although certain cosmetic treatments (e.g. dyeing hair) can interfere with this.[8][9] Notably, basic drugs get incorporated into hair to a greater extent than neutral or acidic drugs, e.g. amphetamines and cocaine are present in higher concentrations in hair compared with benzodiazepines and cannabinoids.[10]

Large-scale drug screening (or urine, hair and other samples) is usually done using enzyme-linked immunosorbent assays (ELISA).[10] Positive ELISA findings are followed by confirmatory testing with liquid chromatography–mass spectrometry (LC-MS) or gas chromatography–mass spectrometry (GC-MS).[9] Chromato-mass-spectrometry is less likely to result in false positive findings than ELISA, but the former requires expensive equipment and highly trained personnel.

The judicial admissibility of the test in the United States is guided by the Daubert standard. A notable court case was United States v. Medina, 749 F.Supp. 59 (E.D.N.Y.1990).[11][12]

Microscopic hair analysis in forensics

El análisis microscópico del cabello consiste en la comparación de varios mechones de cabello bajo un microscopio y la determinación de si las características físicas de cada cabello individual son consistentes entre sí o no. Fue aceptado como ciencia forense en la década de 1950. [ 13 ] Los investigadores a menudo monitoreaban más de una docena de atributos, incluyendo la distribución del pigmento y los patrones de escamas. Esta técnica se ha utilizado en investigaciones criminales para intentar vincular el cabello encontrado en la escena de un crimen u otro lugar de interés, y confirmar si el cabello coincide con el de un sospechoso. Si bien una simple coincidencia de color de cabello podría ser consistente con que un sospechoso determinado haya estado en la escena (cabello negro en la escena cuando el sospechoso tiene cabello negro), el análisis microscópico del cabello comenzó a exigir un estándar más riguroso en la década de 1970. En lugar de simplemente "reducir el campo" de posibilidades, los analistas de cabello afirmaban poder identificar a una persona específica, de modo que el cabello podría ser "prueba" de la presencia de un sospechoso específico. Si bien los informes mecanografiados a menudo matizaban la certeza del análisis microscópico del cabello, los testigos en los tribunales no siempre eran tan modestos. El director del laboratorio forense del estado de Montana testificó que había una "probabilidad de 1 entre 10 000" de que los cabellos encontrados en la escena de un crimen no pertenecieran al sospechoso en un caso, por ejemplo. [ 14 ]

El análisis microscópico del cabello también tiene una larga tradición en la ficción policíaca; se popularizó originalmente en la serie de Sherlock Holmes antes de ser ampliamente utilizado por la policía. [ 13 ] Los programas de televisión de ficción que involucran procedimientos policiales y detectives han continuado utilizándolo desde entonces, incluyendo Columbo , Quincy, ME , Dexter y CSI . [ 14 ]

In hair analysis, it is a basic requirement and a needed skill to be able to distinguish between what is human hair and what is animal or non human hair. To firstly determine the nature of these hairs it is necessary to do a visual examination of the hairs following with a low-power microscopic examination.[4][15] When comparing the medulla if its present, central core of the hair shaft there is a measurement between the relative diameter of the medulla when compared to the overall hair diameter which is the medullary index.[15] This is also a key difference between both hairs as human medullary indexed are around 1/3 index and animal hairs are usually over 1/2 index.[15] This may not be the most reliable analysis up to date as the medulla can or cannot be present and varies between individuals. Another method would be to examine and look at the scale patterns found within the cuticle of the hair.

The cuticle is the outermost layer of the hair shaft,[4] within the cuticle there are scale patterns which can help identify the origin of the hair, whether it is human hair or not. These are the different types of scale patterns observed on hair and how theses can help in the identification of its origin with the use of microscopic analysis;

  • Coronal patterns: Often never found on human hairs, they can be found on small rodents and bats. They're usually found on hairs of very fine diameter. This scale pattern resembles a stack of cups or crowns.[15]
  • Imbricate patterns: Mostly found on human hairs and have scales that overlap laterally and longitudinally to encircle and enclose the cortex.[15]
  • Spinous patterns: Never found on human hairs and are more seen in animal hairs. This pattern exhibits triangular shaped scaled which often protrude from the hair shaft.[15]

All of these differentiation factors and examinations points will help determine whether the hair is human or non human thanks to microscopic analysis.

Microscopic analysis is not widely accepted in the court of law anymore. It is not individualizing enough, therefore it is used to eliminated individuals of interest. Hair microscopy analysis cannot uniquely identify an individual.[16] DNA analysis and Chemical analysis are more accepted in the court of law as they are more accurate in results and can determine a conclusive answer. U.S. Department of Justice guidelines cite that "hair comparison has been demonstrated to be a valid and reliable scientific methodology, although microscopic hair comparison cannot lead to person identification and it is crucial that this limitation be conveyed."

The image depicts different properties that make up a strand of hair.

Skepticism about the stronger claims used by witnesses in the 1970s and 1980s existed at the time. Researchers said in 1974 that the whole process was inherently subjective, and the FBI wrote in 1984 that hair analysis cannot positively match one single person.[13] In the 1990s, DNA profiling was introduced as a key new technique into forensics investigations; it introduced a new level of certainty about matching suspects to evidence. DNA analysis of old cases from the 1970s and 80s, however, contradicted conclusions about a number of earlier matches on the basis of hair analysis.[17]

In 1994, the Justice Department created a task force which would eventually review 6,000 cases by 2004, focusing on the work of one particularly zealous examiner, Michael Malone.[13] These reviews came after reports that sloppy work by examiners at the FBI lab was producing unreliable forensic evidence in court trials. At first, these investigations were largely kept quiet; The Washington Post reported that "Instead of releasing those findings, they made them available only to the prosecutors in the affected cases."[13] A study of FBI Laboratory hair analysis cases between 1996 and 2000 was released in 2002 by Max M. Houck and Bruce Budowle.[18] The study showed that 11% of hair analysis "matches" were contradicted by DNA analysis. As the set of cases analyzed was one which would be expected to favor matches strongly in any case – only hair of individuals the police already believed to be potential suspects was sent in – this error rate was considered to be extremely high.[13]

Kirk L. Odom was convicted of rape in Washington, DC in 1982 by no physical evidence except microscopic hair analysis performed by the FBI Crime Laboratory.[13] Combined with a witness's identification in a line-up (another technique which modern research has shown to be much less reliable than previously thought), Odom was sentenced to twenty or more years in jail. DNA analysis, however, proved that Odom was entirely innocent.[14] While Odom had been released from prison in 2003, he was officially exonerated in 2012 and was paid a large settlement by the city.[19]

In a similar case, Santae Tribble was convicted in 1979 at the age of 17 in Washington, DC of murder due to FBI testimony in a hair analysis match of hair found at the scene. But he had three witnesses who gave him an alibi for the time when the crime was committed. The prosecutor overstated the reliability of hair analysis in identifying a single person, saying in his closing statement that "There is one chance, perhaps for all we know, in 10 million that it could [be] someone else's hair."[13] DNA testing in January 2012, however, showed that the prosecution's key piece of evidence, the hair, did not in fact match the defendant. Tribble was fully exonerated in December 2012, having served 28 years in prison that resulted in severe health problems.[20]

The outcry from defense attorneys about the unreliability of hair analysis and overstatement by FBI experts has resulted in the FBI conducting a review of disputed hair analysis matches since 2012. Due to what it found, in July 2013 the Justice department began an "unprecedented" review of older cases involving hair analysis, examining more than 21,000 cases referred to the FBI Lab's hair unit from 1982 through 1999.

By 2015, these cases included as many as 32 death penalty convictions, in which FBI experts may have exaggerated the reliability of hair analysis in their testimony and affected the verdict. Of these, 14 persons have been executed or died in prison.[21][22] In 2015, DOJ released findings on 268 trials examined so far in which hair analysis was used (the review was still in progress). The review concluded that in 257 of these 268 trials (95 percent), the analysts gave flawed testimony in court that overstated the accuracy of the findings in favor of the prosecution. About 1200 cases remained to be examined. The department emphasized its commitment to following up on these cases to correct any wrongs, saying that they "are committed to ensuring that affected defendants are notified of past errors and that justice is done in every instance. The department and the FBI are also committed to ensuring the accuracy of future hair analysis, as well as the application of all disciplines of forensic science."[21]

In 2017, new Attorney General Jeff Sessions, appointed by President Donald Trump, announced that this investigation would be suspended, at the same time that he announced the end of a forensic science commission that had been working to establish standards on several tests and to improve accuracy; it was a "partnership with independent scientists to raise forensic science standards".[23] Independent scientists, prosecutors, defense counsel and judges criticized ending the commission, saying that the criminal justice system needed to rely on the best science.

As of late 2019, 75 people who were convicted of a crime based on microscopic hair comparison were subsequently exonerated.[24] Another notable case that received media attention since was Anthony Broadwater, who had been convicted of raping Alice Sebold in 1982, and was formally exonerated in 2021 after finishing his time in 1998. The only physical evidence the prosecution offered in 1982 was a hair analysis that was "consistent" with Broadwater. More alarmingly, the only reason the case was re-examined was the unusual fact that Sebold had written an extensive memoir of her experiences (Lucky), which allowed later investigators to uncover major problems with the case.[25]

In environmental toxicology

Analysis of hair samples has many advantages as a preliminary screening method for the presence of toxic substances deleterious to health after exposures in air, dust, sediment, soil and water, food and toxins in the environment. The advantages of hair analysis include the non-invasiveness, low cost, and the ability to measure a large number of, potentially interacting, toxic and biologically essential elements. Hence, head hair analysis is increasingly being used as a preliminary test to see whether individuals have absorbed poisons linked to behavioral or health problems.[1]

Detection of long-term elemental effects

The use of hair analysis appears to be valid for the measurement of lifelong, or long-term heavy metal burden, if not the measurement of general elemental analysis. Several studies, including the analysis of Ludwig van Beethoven's hair, have been conducted in conjunction with the National Institutes of Health and Centers for Disease Control and Prevention.

In a 1999 study on hair concentrations of calcium, iron, and zinc in pregnant women and effects of supplementation, it was concluded that "From the analyses, it was clear that hair concentrations of Ca, Fe, and Zn could reflect the effects of supplementation... Finally, it could be concluded that mineral element deficiencies might be convalesced by adequate compensations of mineral element nutrients."[26]

Occupational, environmental and alternative medicine

El análisis capilar se ha utilizado en medicina ocupacional, [ 27 ] ambiental y en algunas ramas de la medicina alternativa como método de investigación para ayudar en la detección y/o el diagnóstico . Se toma una muestra de cabello, se procesa y se analiza, estudiando los niveles de minerales y metales en la muestra. Utilizando los resultados, como parte de un protocolo de examen o prueba adecuado, [ 28 ] los profesionales detectan la exposición a toxinas y la intoxicación por metales pesados . Algunos defensores afirman que también pueden diagnosticar deficiencias minerales y que las personas con autismo tienen contenidos minerales inusuales en el cabello. [ 29 ] Estos usos suelen ser controvertidos, y la Asociación Médica Estadounidense declara: «La AMA se opone al análisis químico del cabello como determinante de la necesidad de terapia médica y apoya la información al público estadounidense y a las agencias gubernamentales pertinentes sobre esta práctica no probada y su potencial para el fraude en la atención médica». [ 30 ] Una revisión reciente de la literatura científica realizada por el Dr. Kempson destacó que el análisis de metales/minerales en el cabello puede aplicarse en estudios de grandes poblaciones para investigar la epidemiología y grupos de poblaciones crónicamente expuestas; sin embargo, no es posible realizar un diagnóstico individual basado en el cabello. [ 31 ] Una excepción a esto puede ser en análisis avanzados para intoxicaciones agudas. [ 32 ]

Literatura

  • Pragst F., Balikova MA: Estado del arte en el análisis del cabello para la detección del abuso de drogas y alcohol; Clinica Chimic Acta 370 2006 17–49.
  • Auwärter V.: Fettsäuremethylester als Marker exzessiven Alkoholkonsums – Analytische Bestimmung im Haar und in Hautoberflächenlipiden mittels Headspace-Festphasenmikroextraktion und Gascromatografía-Massenspektrometrie. Disertación Humboldt-Universität Berlín 2006.
  • Pragst F.; Auwärter V.; Kiessling B.; Dyes C. (2004). "Prueba de frotis y prueba de parche para el abuso de alcohol basada en la relación de concentración de ésteres etílicos de ácidos grasos y escualeno CFAEE/CSQ en los lípidos de la superficie de la piel". Forensic Sci Int . 143 ( 2–3 ): 77–86 . doi : 10.1016/j.forsciint.2004.02.041 . PMID 15240027 . 

Referencias

  1. 12Masters, Rogers D. "Validity of Head Hair Analysis and Methods of Assessing Multiple Chemical Sensitivity". Dartmouth College. Archived from the original on September 3, 2005. Retrieved December 9, 2006.
  2. ↑Dartmouth Toxic Metals Research Program. A Metals Primer. Archived November 26, 2006, at the Wayback Machine Center for Environmental Health Sciences at Dartmouth. Accessed December 9, 2006.
  3. 123Kintz, Pascal (2019). "Hair analysis in forensic toxicology". WIREs Forensic Science. 1. doi:10.1002/wfs2.1196.
  4. 12345678Tamilmani, K (2017), "Examination of Fetus", Practical Guide for Forensic Medicine and Toxicology, Jaypee Brothers Medical Publishers (P) Ltd., p. 55, doi:10.5005/jp/books/12980_8, ISBN 978-93-86261-52-6, retrieved March 31, 2025
  5. ↑Welch M.J.; Sniegoski L.T.; Allgood C.C.; Habram M. (1993). "Hair analysis for drugs of abuse: Evaluation of analytical methods, environmental issues, and development of reference materials". J Anal Toxicol. 17 (7): 389–398. doi:10.1093/jat/17.7.389. PMID 8309210.
  6. ↑Balikova Marie (2005). "Hair Analysis for Drugs of Abuse: Plausibility of Interpretation". Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub. 149 (2): 199–207. doi:10.5507/bp.2005.026. PMID 16601756.
  7. ↑Høiseth, Gudrun; Arnestad, Marianne; Karinen, Ritva; Morini, Luca; Rogde, Sidsel; Sempio, Cristina; Vindenes, Vigdis; Øiestad, Åse Marit Leere (September 14, 2017). "Is Hair Analysis Useful in Postmortem Cases?". Journal of Analytical Toxicology. 42 (1): 49–54. doi:10.1093/jat/bkx077. ISSN 0146-4760. PMID 28977558.
  8. ↑Gautam, Lata; Cole, Mike (September 13, 2013). "Hair Analysis in Forensic Toxicology". Forensic Magazine. Archived from the original on April 2, 2021. Retrieved August 13, 2014.
  9. 12Usman, Muhammad; Naseer, Abid; Baig, Yawar; Jamshaid, Tahir; Shahwar, Muhammad; Khurshuid, Shazia (April 27, 2019). "Forensic toxicological analysis of hair: a review". Egyptian Journal of Forensic Sciences. 9 (1). doi:10.1186/s41935-019-0119-5. ISSN 2090-5939. S2CID 150379671.
  10. 12Cooper, Gail Audrey Ann (2011). "Hair testing is taking root". Annals of Clinical Biochemistry: International Journal of Laboratory Medicine. 48 (6): 516–530. doi:10.1258/acb.2011.011112. PMID 21868416.
  11. ↑Atlantic Reporter: Second series, Volume 681. West Pub. Co. 1996. p. 44
  12. ↑"Nevada Employment Security Department v. Cynthia Holmes"Archived March 21, 2012, at the Wayback Machine, Kamer Zucker Abbott. 1996. Accessed March 21, 2011
  13. 12345678Hsu, Spencer (April 16, 2012). "Convicted defendants left uninformed of forensic flaws found by Justice Dept". The Washington Post. Retrieved August 31, 2014.
  14. 123Haberman, Clyde (May 18, 2014). "DNA Analysis Exposes Flaws in an Inexact Forensic Science". The New York Times. Retrieved August 31, 2014.
  15. 123456Zeng, Jinhua; Qiu, Xiulian (December 29, 2022). "Forensic authenticity examination of PDF documents". In Lu, Yingfa; Cheng, Changbo (eds.). Third International Conference on Computer Science and Communication Technology (ICCSCT 2022). SPIE. p. 166. doi:10.1117/12.2662214. ISBN 978-1-5106-6124-0.
  16. ↑Norton, Jim; Anderson, William E.; Divine, George (2016). "Flawed forensics: Statistical failings of microscopic hair analysis". Significance. 13 (2): 26–29. doi:10.1111/j.1740-9713.2016.00897.x. ISSN 1740-9713.
  17. ↑Toobin, Jeffery (April 30, 2007). "The CSI Effect". The New Yorker. Retrieved April 6, 2020.
  18. ↑Houck, Max; Budowle, Bruce (2002). "Correlation of microscopic and mitochondrial DNA hair comparisons". Journal of Forensic Sciences. 47 (5): 964–967. doi:10.1520/JFS15515J. PMID 12353582.
  19. ↑Hsu, Spencer (July 10, 2012). "Kirk Odom, who served 20 years for 1981 D.C. rape, is innocent, prosecutors say". The Washington Post. Retrieved August 31, 2014.
  20. ↑Hsu, Spencer (December 14, 2012). "Santae Tribble cleared in 1978 murder based on DNA hair test". The Washington Post. Retrieved August 31, 2014.
  21. 12Hsu, Spencer (April 18, 2015). "FBI admits flaws in hair analysis over decades". The Washington Post. Retrieved April 22, 2015.
  22. ↑Hsu, Spencer (July 17, 2013). "U.S. reviewing 27 death penalty convictions for FBI forensic testimony errors". The Washington Post. Retrieved August 31, 2014.
  23. ↑Hsu, Spencer (April 18, 2017). "Sessions orders Justice Dept. to end forensic science commission, suspend review policy". The Washington Post. Retrieved April 18, 2017.
  24. ↑Colloff, Pamela (December 20, 2018). "Bloodstain Analysis Convinced a Jury She Stabbed Her 10-Year-Old Son. Now, Even Freedom Can't Give Her Back Her Life". propublica.org. ProPublica. Archived from the original on January 16, 2020. Retrieved January 16, 2020.
  25. ↑ Knoll, Corina; Zraick, Karen; Alter, Alexandra (15 de diciembre de 2021). "Fue declarado culpable de violar a Alice Sebold. Luego el caso se desmoronó" . The New York Times . Consultado el 8 de enero de 2022 .
  26. ↑ Leung, PL; Huang, HM; Sun, DZ; Zhu, MG (septiembre de 1999). "Concentraciones de calcio, hierro y zinc en el cabello de mujeres embarazadas y efectos de la suplementación". Biol Trace Elem Res . 69 (3): 269–82 . Bibcode : 1999BTER...69..269L . doi : 10.1007/BF02783879 . PMID 10468164. S2CID 21247500 .  
  27. ^ Niculescu, T; Dumitru, R; Botha, V; Alexandrescu, R; Manolescu, N (febrero de 1983). "Relación entre la concentración de plomo en el cabello y la exposición ocupacional" . Hno. J Ind Med . 40 (1): 67– 70. doi : 10.1136/oem.40.1.67 . PMC 1009120 . PMID 6824602 .  
  28. ↑ Bass DA, Hickok D, Quig D, Urek K. Análisis de oligoelementos en el cabello: factores que determinan la exactitud, precisión y fiabilidad – Datos estadísticos incluidos. Archivado el 11 de noviembre de 2006 en Wayback Machine Altern Med Review 2001;6(5):472–481.
  29. ↑ Lathe, Richard y Michael Le Page. «Pista de metales tóxicos para el autismo: un estudio ha revelado sorprendentes diferencias en los niveles de mercurio en el cabello de niños autistas y niños normales. (This Week)». New Scientist 178.2400 (21 de junio de 2003): 4(2).
  30. ↑ Análisis capilar: Un posible abuso médico. Política número H-175.995, (Sub. Res. 67, I-84; Reafirmada por CLRPD Rep. 3 – I-94)
  31. ↑ Kempson IM, Lombi E. (2011). "Análisis del cabello como biomonitor para toxicología, enfermedad y estado de salud". Chemical Society Reviews . 40 (7): 3915– 3940. doi : 10.1039/C1CS15021A . PMID 21468435 . 
  32. ↑ Kempson IM, Henry DA (2010). "La radiación de sincrotrón revela el envenenamiento por arsénico y su metabolismo en el cabello: el caso de Phar Lap". Angewandte Chemie International Edition . 49 (25): 4237– 4240. doi : 10.1002/anie.200906594 . PMID 20432493 . 

Bibliografía

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