Robert Guthrie and the Birth of Newborn Screening

By Tabitha Pracale-Ocampo

Phenylketonuria (PKU) is an inherited metabolic disorder in which the body cannot properly process phenylalanine, an amino acid found in many foods. Without treatment, phenylalanine can build up in the blood and cause severe neurological damage, including intellectual disabilities and developmental delays. Although PKU can be managed with a phenylalanine-restricted diet, the treatment is most effective when the disorder is identified soon after birth. Before Robert Guthrie developed his newborn screening test, however, PKU was often not diagnosed until after developmental problems had already occurred. Guthrie’s personal experiences with his son, who had an undiagnosed intellectual disability, and his work with children affected by PKU ultimately inspired him to develop a simple, inexpensive method for detecting the disorder in newborns. His pioneering work helped establish newborn screening as an important tool for identifying treatable conditions before they could cause permanent harm.

On June 28, 1916 in the small town of Marionville, Missouri, Ina Florence Ledbetter Guthrie and Reginald Guthrie welcomed their son, Robert Guthrie, into the world. Little did they know he would become known as the “Father of Newborn Screening.” The Guthrie family was not well-off, as Reginald worked as a traveling salesman. The family moved to Minneapolis, Minnesota in 1922 where Robert spent his childhood and early adult life. He was not an exceptional student despite who he would become later in life. He did well in the subjects he enjoyed but did not study for his other classes, and therefore graduated high school towards the bottom of his class in 1935. Due to his poor grades and lack of financial resources, Guthrie did not qualify for admission to university, so he went back to high school as a post-graduate student. He took various classes including algebra and chemistry where he got good grades and then reapplied to university. By the spring of 1936 he began studying at the University of Minnesota under the National Youth Administration (NYA) program, which provided low-income students with federally subsidized jobs at state universities. Under the program he worked with Professor Charles Evans in the Department of Bacteriology and Immunology. The job and his work with Professor Evans inspired Guthrie to major in microbiology. After successfully completing his undergraduate coursework, Guthrie was encouraged by Professor Evans to pursue medical school, so he applied to the University of Minnesota and was accepted in 1939.

Guthrie realized less than a year into medical school that he didn’t like it and wanted to pursue something else. He had a part-time job working for a professor of microbiology, and knowing that Guthrie was unhappy, the professor suggested that he transfer to the University of Maine as a graduate student and even helped him secure a graduate assistant position in the Department of Bacteriology and Biochemistry. Guthrie immediately enjoyed his time there a lot more and felt that he had found his calling with bacteriology. In 1941, he met Margaret Flagstad in an organic chemistry class, and the two married in August of that year. After graduating from his graduate program, Guthrie decided to continue medical school following the advice of his peers and mentors, so he and Margaret returned to Minneapolis. While here, he made the decision to simultaneously work towards his PhD in bacteriology, so in 1946 Guthrie graduated with both an MD and a PhD. Interestingly enough, he never intended on actually practicing medicine, but took his licensing exams seriously in order to appease his father [1]. He always considered his PhD more important than his MD because bacteriology was his true passion. Nonetheless, Guthrie accomplished an amazing feat, earning 6 degrees in 6 years! Between 1941 and 1946 he earned a bachelor’s in bacteriology, a general bachelor’s of science degree he obtained during his second year of medical school, a bachelor of medicine degree, a master’s degree in biochemistry, an MD, and a PhD in bacteriology [1].

 After completing all of his schooling, Guthrie began his professional career as a research microbiologist at the National Institutes of Health (NIH) in Bethesda, Maryland studying protozoan Trichomonas fetus, which causes spontaneous abortions in cattle [2]. He didn’t work here for very long since his supervisor was not supportive of his research projects. In 1949, Guthrie joined the University of Kansas as chairman of the Department of Bacteriology, but didn’t stay here for very long either. Between 1950 and 1954, Guthrie hopped around to different jobs. He worked at the Public Health Service at Staten Island Public Health Hospital supervising the diagnostic bacteriology lab. Then he moved onto the Sloan Kettering Institute in Manhattan where he supervised the diagnostic bacteriology lab there. Not too long after this he began working at the Roswell Park Cancer Institute in Buffalo, New York to develop chemotherapeutic agents to treat cancer. His time and experience here laid the groundwork for his development of the newborn screening test for PKU.

The Guthries settled in Williamsville in upstate New York while Robert Guthrie continued his work of identifying drugs for the treatment of childhood leukemia at Roswell Park. Between 1945 and 1954, Margaret and Robert had six children, including one of their sons, John, who was mentally disabled but never formally diagnosed with a birth defect or disease even after undergoing various tests and seeing specialists [2]. Robert and Margaret became active in the Erie County chapter of NARC because of their son, and if it wasn’t for John, Guthrie may have never become interested in mental disabilities and PKU [1]. In 1957, while serving as vice president of the Erie County NARC chapter, Guthrie met Dr. Robert Warner, director of the Children’s Rehabilitation Center at the University of Buffalo Children’s Hospital. The rehabilitation center focused on diagnosing and evaluating people with intellectual disabilities, including those caused by PKU. Dr. Warner introduced Guthrie to PKU and explained that a phenylalanine-restricted diet could help manage the condition in children. However, monitoring his patients’ blood phenylalanine levels was difficult because each test required 15 to 20 cc of venous blood to be sent to a firm in California [1]. He wanted Guthrie to develop a different method that was inexpensive but still accurate and Guthrie was up for the challenge.

After repeated trial and error, Guthrie developed a simple method of monitoring blood phenylalanine that involved only a few drops of blood. He reported that he could do the test using 3 to 5 drops of capillary blood from a finger prick, which stood in contrast to the method that Warner described. Guthrie’s technique utilized bacterial metabolism by putting a spot of blood on a filter paper disc that he then put on the surface of an agar culture gel. The agar culture gel contained a specific substance to inhibit the growth of bacteria, but which would be reversed by phenylalanine. If excess phenylalanine was present in the blood, it removed the growth inhibition and bacteria grew. Overnight incubation would allow him to examine the sample and compare the diameter of the growth zone around it with a control disc of blood where he added known quantities of phenylalanine. The agar would remain clear except for circles of growth surrounding the discs that contained phenylalanine. He called this technique the “bacterial inhibition assay.” 

In 1958, Guthrie was asked to join the pediatrics department at the Children’s Hospital in Buffalo where he continued to research and develop similar tests for other metabolic disorders that caused intellectual disability using his PKU research as a model. His interest in PKU was reignited when his sister-in-law’s baby was diagnosed with PKU at 15 months old. She was initially diagnosed with an unreliable urine test that was most commonly used at the time, so Guthrie retested her using his bacterial inhibition assay and it confirmed she did indeed have PKU. Because she had already sustained brain damage by the time she was diagnosed, Guthrie became a strong advocate for testing all infants for PKU at birth [1]. The sooner a diagnosis was made and treatment started, the better the prognosis would be for intellectual growth. Guthrie also decided to revise his test and found that he could blot a piece of filter paper directly on a small heel puncture wound, dry the blood sample and then punch out a small disc from the blood spot and proceed as usual with the rest of the test. This method proved to be successful after it underwent clinical trials to prove its safety and efficacy. He tested it on 3,000 residents of a state school for mentally disabled youth near Rochester, New York [2]. His test detected 23 cases of PKU when the traditional test only detected 19 cases, showing that his method was more accurate than the traditional urine test. In 1961, NARC held a press conference at its annual meeting in San Francisco to publicize the Guthrie test and Guthrie went around the world to campaign for universal screening.

Guthrie’s PKU test was not widely accepted by the medical community without some initial pushback. Several medical professionals claimed the test was inaccurate and in a 1962 article in the Atlantic Monthly, some went as far to argue that Guthrie and Warner should be prosecuted for wrongly diagnosing infants with PKU [2]. Others considered routine screening to be “socialized medicine” and an infringement on the private practice of medicine [3]. In 1963 the test began to receive some acceptance among scientists after Guthrie and his colleague, Ada Susi, published an article in Pediatrics about the Guthrie test [2]. However, the article was not enough to completely change the sentiment surrounding testing, since in 1964, the House of Delegates of the American Medical Association voted to oppose “legislation requiring compulsory testing” for PKU and state medical societies, besides in Massachusetts, also continued to oppose mandated screening. The biggest opposition for PKU screening was Dr. Samuel Besman, a medical researcher who argued that compulsory newborn screening for PKU was not only unjustified, but that even dietary treatment for PKU was unjustified [3]. However, with continued advocacy and long term proof of the effectiveness of the Guthrie PKU test and newborn screening, by 1966 newborn screening was mandatory in most states. As stated by Harvey Levy, an American biochemical geneticist, pediatrician, and physician scientist, “No matter the opposition or, at times, even vitriol leveled against him, he never lost his composure or his unwavering focus on newborn screening. In fact, to call his dedication to newborn screening a ‘focus’ does not adequately describe the intensity of his focus” [3]. 

Guthrie’s contributions to newborn screening extended far beyond his work on PKU. He and his laboratory personnel eventually developed tests for more than 30 treatable conditions that could cause intellectual disabilities or death, including galactosemia and maple syrup urine disease, using bacterial inhibition assays. In 1975, Guthrie became a consultant for the California Department of Health in Sacramento, where he also advocated for the investigation of lead poisoning in children. Guthrie continued his work in newborn screening and public health until his death on June 24, 1995, in Seattle, Washington. Although new technologies have since made the Guthrie test largely obsolete in most developed countries, the development of these more advanced screening methods would not have been possible without the foundation Guthrie established. His dedication to early diagnosis and treatment transformed newborn screening and ultimately helped prevent countless cases of intellectual disability and death.

Bibliography:

[1] Koch, Jean Holt. “The PKU Story: Bob Guthrie and Phenylketonuria.” Robert Guthrie Legacy Project. Accessed July 22, 2026. https://www.robertguthriepku.org/professional.

[2] Zhu, Melilin. “Robert Guthrie (1916-1995).” Arizona State University. Last modified February 23, 2017. https://embryo.asu.edu/pages/robert-guthrie-1916-1995.

[3] Levy, Harvey L. “Robert Guthrie and the Trials and Tribulations of Newborn Screening.” International journal of neonatal screening vol. 7,1 5. 19 Jan. 2021, doi:10.3390/ijns7010005.