Amino acid profiles by HPLC after filter paper sampling: 'appropriate technology' for monitoring of nutritional status

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

Causes of delay in referral of patients with phenylketonuria to a specialized reference centre in Mexico

Objective

To expose causes leading to the delayed arrival of phenylketonuria (PKU) patients at a governmental reference centre (RC), and to describe their clinical characteristics.

Material and methods

PKU files registered during the past 18 years at the National Institute of Pediatrics in Mexico City were evaluated. Patients were classified into two groups according to their age at arrival: Group I (early reference), patients arriving during the first month of life; and Group II (late reference), those who arrived after thirty days of age. Time and causes of delay were documented.

Results

Of 57 recorded files, 10 were classified in Group I and 47 in Group II. Causes leading to the late arrival of Group II patients were absence of routine newborn screening (NBS), PKU not included in the routine NBS, sampling after the recommended age, false negative result, results without interpretation and/or instructions to follow, delayed notification of results, poor medical criteria of attending physician, difficulties in obtaining confirmatory tests, and administrative failures.

Conclusion

The main cause of late referral of PKU patients was the absence of PKU testing. As a developing country, Mexico still faces challenges in the proper functioning and expansion of the NBS programme. Most PKU patients arrived at the RC late, presenting with varying degrees of the clinical spectrum. Incorporating PKU testing into the already established Mexican NBS system and adding quality indicators to guarantee proper operation in all NBS phases is necessary to achieve the goal of identifying, referring, diagnosing, and treating patients promptly.

Effect of supplementation during pregnancy with L-arginine and antioxidant vitamins in medical food on pre-eclampsia in high risk population: randomised controlled trial

OBJECTIVE

To test the hypothesis that a relative deficiency in L-arginine, the substrate for synthesis of the vasodilatory gas nitric oxide, may be associated with the development of pre-eclampsia in a population at high risk.

DESIGN

Randomised, blinded, placebo controlled clinical trial.

SETTING

Tertiary public hospital in Mexico City.

PARTICIPANTS

Pregnant women with a history of a previous pregnancy complicated by pre-eclampsia, or pre-eclampsia in a first degree relative, and deemed to be at increased risk of recurrence of the disease were studied from week 14-32 of gestation and followed until delivery.

INTERVENTIONS

Supplementation with a medical food-bars containing L-arginine plus antioxidant vitamins, antioxidant vitamins alone, or placebo-during pregnancy.

MAIN OUTCOME MEASURE

Development of pre-eclampsia/eclampsia.

RESULTS

222 women were allocated to the placebo group, 228 received L-arginine plus antioxidant vitamins, and 222 received antioxidant vitamins alone. Women had 4-8 prenatal visits while receiving the bars. The incidence of pre-eclampsia was reduced significantly (χ(2) = 19.41; P < 0.001) in women randomised to L-arginine plus antioxidant vitamins compared with placebo (absolute risk reduction 0.17 (95% confidence interval 0.12 to 0.21). Antioxidant vitamins alone showed an observed benefit, but this effect was not statistically significant compared with placebo (χ(2) = 3.76; P = 0.052; absolute risk reduction 0.07, 0.005 to 0.15). L-arginine plus antioxidant vitamins compared with antioxidant vitamins alone resulted in a significant effect (P = 0.004; absolute risk reduction 0.09, 0.05 to 0.14).

CONCLUSIONS

Supplementation during pregnancy with a medical food containing L-arginine and antioxidant vitamins reduced the incidence of pre-eclampsia in a population at high risk of the condition. Antioxidant vitamins alone did not have a protective effect for prevention of pre-eclampsia. Supplementation with L-arginine plus antioxidant vitamins needs to be evaluated in a low risk population to determine the generalisability of the protective effect, and the relative contributions of L-arginine and antioxidant vitamins to the observed effects of the combined treatment need to be determined. Trial registration Clinical trials NCT00469846.

Determination of amino acids by ion-exchange chromatography on filter paper spotted blood samples stored at different temperatures and for different periods: comparison with capillary and venous blood

OBJECTIVE

To determine whether the well-established filter paper spotted blood method used for the determination of some amino acids could be reliably used to measure all amino acids and whether amino acid results thus obtained are reproducible and comparable to the results obtained by measuring plasma amino acids in either capillary or venous blood.

METHODS

This is a prospective study in which blood samples from a finger-prick were collected in capillary tubes and at the same time blotted on filter papers; another sample was taken from a vein, from 19 healthy volunteers aged between 18 and 24 yr after a strict 12-h overnight fast. Another 9 healthy adult volunteers provided blood samples on filter papers for the storage study; 9 samples were analyzed immediately; 9, 8 and 4 samples were stored at -20 degrees C, -4 degrees C and room temperature respectively and analyzed after 14 days; 8 samples stored at -20 degrees C were analyzed after 4 weeks.

RESULTS

Intra-sample reproducibility in the filter paper blood from the same individual was found to be mostly less than 20%, while for the capillary blood was less than 5%. The greatest variability was in cystine and methionine. There was no significant difference between results obtained from capillary blood and from venous blood, but there was a significant difference between amino acid concentrations in venous and capillary blood on the one hand and filter paper blood on the other. Storage at different temperatures and for a varied period of time showed little change except in serine, glutamate, ornithine, histidine, cystine and methionine. There was a 30% decrease in concentrations of most amino acids in filter paper blood when compared to capillary or venous blood probably because of loss in the extraction process.

CONCLUSION

A new set of values for amino acids in filter paper blood in normal individuals is presented. Blood spotted filter paper could be used to screen practically all inborn errors of amino acid metabolism.

Multivariate discrimination for phenylketonuria (PKU) and non-PKU hyperphenylalaninemia after analysis of newborns’ dried blood-spot specimens for six amino acids by ion-exchange chromatography

Ion-exchange HPLC was developed for testing dried blood-spot specimens from newborns. The method is suitable for quantitative confirmatory testing of abnormal specimens detected in the New York State Newborn Screening Program. Positive specimens were initially identified among all New York State newborns with semiquantitative bacterial inhibition assays (BIA) for aminoacidopathies, including phenylketonuria (PKU) and non-PKU hyperphenylalaninemia (HP), maple syrup urine disease, and homocystinuria. A selection of 1346 specimens from routine BIA screening, including 131 newborns with PKU or persistent HP, were tested by HPLC. Of 179 BIA results that were falsely positive, 98 (55%) were also falsely positive by HPLC in which the Phe/Tyr ratio was the discriminator and the threshold was set to attain 100% sensitivity. Investigation of three multivariate discriminatory methods revealed that linear discriminant analysis excluded all but 35 (20%) of the BIA false-positives.