Better Blood Sample Quality Control with Metabolomics
A new protocol could bring the benefits of Metabolomic screening to routine, high-volume blood sample quality control
May 26, 2022
High-quality biospecimens are crucial to obtaining reproducible test results in fields such as blood banking, clinical diagnostic testing, and research. Sample quality can present a real problem for labs working with human blood and tissue samples as the test center often has no control over the collection process or the handling and transportation that occurs between a sample being taken and receipt of that sample at the testing lab. Even though blood plasma is the most common biospecimen used in research and health care the processing of blood to plasma remains exposed to multiple sources of pre-analytical errors and variations that can materially affect the result of an analytical test. It has been reported that pre-analytical errors occur in up to 5.5% of in-patient diagnostic tests, and account for 46 – 68% of diagnostic errors. One of the most common pre-analytical quality issues in clinical diagnostic testing is the delay in the processing of blood samples into the plasma used in testing.
Current methods of quality control are less than perfect
The current standard for quality control of incoming biospecimens is the use of specific test methods to test for individual issues which requires an a priori knowledge of the issue being tested for. The specificity of these tests means that while they can provide insight into a specific condition that may affect sample quality, they provide no other information in regards to the quality of the sample, allowing low-quality samples to continue into analytical testing unchallenged, with a knock-on negative effect on the test result, and potentially deleterious effect on the health of a patient.
A simple rapid technique for metabolomic screening of blood serum samples
Metabolomics would be an ideal solution to this problem, capable of detecting the state of thousands of small molecules within a sample at the same time, and would enable a broad-based assessment of the vitality of a serum sample without the need for an a priori understanding of what the problem might be. Up until now the cost and complexity of the techniques used for metabolomics have created a barrier to its use in this type of high volume, cost-sensitive environment.
In a recent paper, Bordaget al. described a rapid, affordable, and simple technique for the testing of serum samples in high throughput applications such as clinical diagnostic testing, research, and biobanking utilizing Probe Electrospray Ionization Mass Spectrometry (PESI-MS) to generate the metabolomic data from the blood serum samples.
Simple robust metabolomics with PESI-MS
PESI-MS is a rapid, robust and simple technique in Mass Spectrometry, that can produce large amounts of data using simplified sample handling and processing to deliver results in just minutes using an automated platform suitable for high volume sample processing.
In contrast to Liquid Chromatography Mass Spec, PESI-MS eliminates the chromatography step, using instead a collection needle dipped vertically into the sample to remove a very small test volume, as small as just 1 or 2 μL. The electrospray is then created by applying a high voltage to the needle and the dispersal pattern created by thousands of small molecules is recorded. It is the simplicity of the technique that allows its applications in areas that would typically be outside the scope of traditional Mass Spectrometry.
Making PESI-MS work for routine sample testing
The authors used a deliberately simple setup, coupling PESI to a single-quad mass spectrometer, and deliberately avoiding more sophisticated detectors in order to demonstrate the capability of the technique using inexpensive detection equipment available to most labs, and critically, technology that does not require extensive user expertise to produce results. To make the protocol practical for routine use in a high throughput setting the authors needed to keep the protocol simple and automation-friendly. Purposely omitting steps that required long incubations or evaporation to dryness and opting instead to prepare samples using filtration. The authors selected a single-step, direct precipitation using AcroPrepTM Advance 96-well, 0.2 μm filter plates to concentrate samples prior to PESI-MS. The compatibility of the filter plates with either vacuum or positive pressure being crucial for automation in a high throughput environment. Maintaining the same 96-well format throughout the protocol also serves to simplify the processing for busy labs.
The study focused on one of the most common pre-analytical problems for blood plasma, the time delay between blood collection and plasma processing. The intent of the study was to determine whether the PESI-MS technique could robustly identify samples that had suffered time delays of 3 hours between collection and processing. In the experiment, the authors processed human blood samples (n=50) into serum for testing. Splitting each sample and processing half immediately, and the other half after a 3-hour delay. The PESI-MS method only requires 2 μL of plasma for each test and can be run in both ionization modes in just 2 minutes. This high-speed, low-volume testing enables three replicate measurements to be made in six minutes using only a tiny fraction of the total sample.
Finding a fingerprint for good and bad samples
The mass spectra produced contained 1200 stable features covering a broad spectra of metabolic classes. The team identified 18 of these features that were altered in samples that had suffered a delay between blood draw and serum processing. Using automated analysis software the authors were able to distinguish the delayed samples with an AUC of > 0.95%. (Area Under the Curve or Concordance Value). Significantly, detection was proof against the loss or failure of one out of the three replicate tests for each sample, indicating a level of robustness that is important in front-line testing in a high-throughput environment where some tests will inevitably fail.
The results of this experiment prove the potential of PESI-MS as a fully automated, low-cost technique for the assessment of human blood samples. Enabling replacement of the existing specific tests with a metabolomic approach that is simple, robust, inexpensive, and requires just a few microliters of serum sample to provide definitive results with a high degree of statistical confidence.
You can find out more about the AcroPrep Advance filter plates used in this study, as well as other specialist filtration products on the Pall Website.