Use of the Guthrie bacterial inhibition assay to monitor blood phenylalanine for dietary treatment of phenylketonuria

Rohr, Frances J.; Allred, Elizabeth N.; Turner, Melissa; Simmons, Jane; Levy, Harvey L.

doi:10.1016/0925-6164(96)00130-2

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Volume 4, Issue 4 , Pages 205-211, May 1996

Use of the Guthrie bacterial inhibition assay to monitor blood phenylalanine for dietary treatment of phenylketonuria

Frances J. Rohr
- Genetic Service, I.C. Smith 106, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
Elizabeth N. Allred
- Neuroepidemiology Service, Children's Hospital, 300 Longwood Avenue Boston, MA 02115, USA
Melissa Turner
- Genetic Service, I.C. Smith 106, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
Jane Simmons
- NE Regional Newborn Screening Program, State Laboratory Institute, Boston, MA, USA
Harvey L. Levy
- Genetic Service, I.C. Smith 106, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA, USA
- NE Regional Newborn Screening Program, State Laboratory Institute, Boston, MA, USA
- Corresponding author. Tel: + 1-617-3556346: Tel: + 1-617-7300461.

Received 29 August 1995; received in revised form 19 December 1995; accepted 23 December 1995.

Abstract

Introduction: The need to maintain blood phenylalanine levels in the range of 2–6 mg/dl (120–360 μM) for metabolic control in dietary treated phenylketonuria (PKU) requires weekly or biweekly monitoring of the blood phenylalanine level. This is greatly facilitated by filter paper blood collection in the home and testing in a newborn screening program. For over 25 years, we have used the Guthrie bacterial inhibition assay (GBIA) for this purpose and report our results in comparison with amino acid analyzer (AAA) results. Methods: Plasma phenylalanine was measured by the amino acid analyzer and blood phenylalanine in dried blood spots was measured by GBIA in paired specimens. Recording of values was performed blinded. Results: 969 paired blood specimens were tested from individuals with PKU both on and off diet. In 85% of the specimens, the GBIA phenylalanine values were in the same category of < 2, 2–6. or > 6 mg/dl (< 120, 120–360, > 360 μM) as the AAA value. In 85% of the specimens in which the GBIA value was out of metabolic control range (< 2 or > 6 mg/dl; < 120 or > 360 μM), the AAA value was also out of range and in 84% of the paired specimens when the GBIA value was in range (2–6 mg/dl; 120–360 μM), the AAA value was also in range. When the GBIA and AAA values differed, the difference was less than 2 mg/dl (< 120 μM) most of the time. Discussion: These results indicate that the GBIA for phenylalanine can be used to monitor the diet in PKU. The advantages this test provide include simple collection in the home, thus facilitating frequent monitoring, use and transport of the relatively safe filter paper blood specimen as opposed to the biohazards of a liquid blood specimen, and efficient and inexpensive testing in a newborn screening program.

Keywords: Phenylketonuria, Phenylketonuria (PKU), Guthrie test, Bacterial inhibition assay, Diet, Phenylalanine

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