Clinical chemistry and dried blood spots: increasing laboratory utilization by improved understanding of quantitative challenges

Quantitation of phenylalanine and tyrosine from dried Blood/Plasma spots with impregnated stable isotope internal standards (SIIS) by FIA-SRM

BACKGROUND

Dried Blood Spot (DBS) analysis has been used for identification and quantification of diseases and disorders in large populations. Simply collecting blood or plasma samples on cotton paper, followed with an organic solvent extraction, many small molecules can be detected and quantified. In a typical procedure of DBS analysis in newborn screening, stable isotope internal standards (SIIS) are added to extraction solvent as a reference. However, this way of employing SIIS does not reflect extraction efficiency, or protein binding issues, nor does it reflect potential degradation that could occur. In addition, punched-out discs from larger DBS are known to have imprecision typically ≥ 15%.

METHODS

We developed and tested an approach, internal quantitative DBS (iqDBS), which delivers an exact volume of whole blood or plasma to a paper disc that is impregnated with a dried concentration of SIIS for quantitation. Amino acids were derivatized to make butyl esters and measured using Flow Injection Analysis with Selected Reaction Monitoring (FIA-SRM).

RESULTS

We demonstrated with phenylalanine and tyrosine improved sensitivity and accuracy by applying iqDBS.

CONCLUSIONS

We established a new method for quantitative analysis of small molecules from dried blood spots that incorporates stable isotope internal standard at the time of blood collection.

Cell Analysis from Dried Blood Spots: New Opportunities in Immunology, Hematology, and Infectious Diseases

Blood cell analysis is a major pillar of biomedical research and healthcare. These analyses are performed in central laboratories. Rapid shipment from collection site to the central laboratories is currently needed because cells and biomarkers degrade rapidly. The dried blood spot from a fingerstick allows the preservation of cellular molecules for months but entire cells are never recovered. Here leucocyte elution is optimized from dried blood spots. Flow cytometry and mRNA expression profiling are used to analyze the recovered cells. 50-70% of the leucocytes that are dried on a polyester solid support via elution after shaking the support with buffer are recovered. While red blood cells lyse upon drying, it is found that the majority of leucocytes are preserved. Leucocytes have an altered structure that is improved by adding fixative in the elution buffer. Leucocytes are permeabilized, allowing an easy staining of all cellular compartments. Common immunophenotyping and mRNAs are preserved. The ability of a new biomarker (CD169) to discriminate between patients with and without Severe Acute Respiratory Syndrome induced by Coronavirus 2 (SARS-CoV-2) infections is also preserved. Leucocytes from blood can be dried, shipped, and/or stored for at least 1 month, then recovered for a wide variety of analyses, potentially facilitating biomedical applications worldwide.

Combining lipidomics and machine learning to measure clinical lipids in dried blood spots

INTRODUCTION

Blood-based sample collection is a challenge, and dried blood spots (DBS) represent an attractive alternative. However, for DBSs to be an alternative to venous blood it is important that these samples are able to deliver comparable associations with clinical outcomes. To explore this we looked to see if lipid profile data could be used to predict the concentration of triglyceride, HDL, LDL and total cholesterol in DBSs using markers identified in plasma.

OBJECTIVES

To determine if DBSs can be used as an alternative to venous blood in both research and clinical settings, and to determine if machine learning could predict 'clinical lipid' concentration from lipid profile data.

METHODS

Lipid profiles were generated from plasma (n = 777) and DBS (n = 835) samples. Random forest was applied to identify and validate panels of lipid markers in plasma, which were translated into the DBS cohort to provide robust measures of the four 'clinical lipids'.

RESULTS

In plasma samples panels of lipid markers were identified that could predict the concentration of the 'clinical lipids' with correlations between estimated and measured triglyceride, HDL, LDL and total cholesterol of 0.920, 0.743, 0.580 and 0.424 respectively. When translated into DBS samples, correlations of 0.836, 0.591, 0.561 and 0.569 were achieved for triglyceride, HDL, LDL and total cholesterol.

CONCLUSION

DBSs represent an alternative to venous blood, however further work is required to improve the combined lipidomics and machine learning approach to develop it for use in health monitoring.

Hematocrit, blood volume, and surface area of dried blood spots - a quantitative model

The use of the dried blood spot (DBS) sampling technique has extended the scope of clinical research, particularly in children. The effects of different hematocrit levels (25-55%) and different blood volumes (7.5-30 μL) on the surface area of the blood spots were investigated using ImageJ® software. Variation in hematocrit levels between patients and inaccuracies in blood volumes applied to Guthrie cards can have a marked effect on analyte concentrations measured in DBS samples. The current study presents a validated model that links blood volume and hematocrit to the surface area of the blood spot. The final model showed that both factors affect the blood spot surface area, however, the positive effect of blood volume is higher than the negative effect of hematocrit. The measurement of surface area could be added as an additional quality control step in clinical studies that have adopted fixed volume DBS sampling for the quantification of the analytes. This approach can be used in estimating the hematocrit if this is not known for a patient or estimating the volume in spots that are visually different in size from the norm, i.e. technical error.

Cortical Pain Response of Newborn Infants to Venepuncture: A Randomized Controlled Trial Comparing Analgesic Effects of Sucrose Versus Breastfeeding

OBJECTIVE

Sucrose administration and breastfeeding decrease behavioral expressions of pain in neonates. However, recent studies indicated that there is a persistent cortical response with sucrose. This study compared the efficacy of sucrose administration versus breastfeeding to decrease cortical responses to pain during venepuncture.

PATIENTS AND METHODS

A randomized, prospective, controlled trial was conducted in a tertiary level maternity ward. Healthy, 3-day-old term neonates, undergoing venepuncture for neonatal screening, were randomly assigned to receive sucrose solution or be breastfed before venepuncture. Variations in the total hemoglobin concentration [HbT] in the contralateral somatosensory cortex were assessed with near infrared spectroscopy. The Neonatal Facial Coding System (NFCS) was used to assess reactions.

RESULTS

There were 114 term neonates included, with 102 included for the primary outcome (breastfed group: 48; sucrose group: 54). Similar maximum increases in [HbT] were observed in both groups (mean±SD: sucrose group: 31.2±58.1 μmol/L; breastfed group: 38.9±61.4 μmol/L; P=0.70). Breastfed neonates presented more behavioral expressions that indicated pain compared with sucrose-administered neonates (46.8% vs. 26.8% of NFCS ≥1, P=0.04). The maximum increase in [HbT] was persistent, although newborn infants who did not express behavioral signs of pain had lower concentrations than neonates who did (mean±SD: 21.2±29.1 vs. 60.0±89.8 μmol/L, P<0.01).

DISCUSSION

There was no difference in the cortical responses to pain during venepuncture in newborn infants who were administered sucrose versus those who were breastfed.

Should phosphatidylethanol be currently analysed using whole blood, dried blood spots or both?

Phosphatidylethanol (PEth) are phospholipids produced through non-oxidative ethanol metabolism. They accumulate in red blood cells and have been traditionally analysed in whole blood as potential biomarkers for moderate to long-term alcohol consumption. More recently, their analysis in dried blood spots has been gaining favour, namely, due to the ease in sampling, transport and storage conditions required. This paper aims at providing a short comparative review between analysing PEth in whole blood and dried blood spots and the potential pitfalls that researchers may face when setting up PEth testing for clinical use.

A DBS method for quantitation of the new oral trypanocidal drug fexinidazole and its active metabolites

AIM

Fexinidazole (FEX) is a nitroimidazole being developed as a new trypanocide treatment for human African trypanosomiasis/sleeping sickness. Its main metabolites, fexinidazole sulfoxide (M1) and fexinidazole sulfone (M2), show the same in vitro pharmacological activity as FEX.

METHODS & RESULTS

An LC-MS/MS assay was developed for quantitation of FEX in DBS, collected via finger-prick from healthy subjects. The DBS assay was specific, accurate and reproducible for FEX, M1 and M2 when validated against the current plasma assay. DBS samples were stable for 24 h at 37°C with 95% relative humidity, and 58 weeks desiccated at room temperature.

CONCLUSION

DBS finger-prick sampling offers a simple, practical method for determining FEX, M1 and M2 concentrations in clinical studies in Africa.