Protocol 2: blood processing into plasma and serum aliquots

protocol
blood processing
plasma
serum
Why two blood fractions feed two different assays and which pre-analytical fields must travel with them
Author

Methylation & Colitis team

Published

August 25, 2026

Purpose

One blood collection produces two distinct analytical materials. Plasma supplies cell-free DNA for EM-seq and fragmentomics; serum supplies sIgA for ELISA. Tube type, clotting, centrifugation, transfer, delay, temperature, freeze–thaw history, aliquot volume, and visible hemolysis belong in the data record.

flowchart LR
  B[Blood collection] --> P[Plasma aliquots]
  B --> S[Serum aliquots]
  P --> C[cfDNA extraction]
  S --> E[sIgA ELISA]

Fraction Immediate output Later data
plasma labeled, frozen aliquots with processing metadata cfDNA yield, methylation counts, plasma fragment features
serum labeled, frozen aliquots with processing metadata replicate OD and calibrated sIgA concentration

QC gate

Processing must prevent cellular carryover into plasma: leukocyte lysis can swamp rare colon-derived cfDNA and distort fragment sizes. Serum conditions must be consistent enough that plate differences are not proxies for clinical group.

ImportantPlasma is not serum

The fractions are not interchangeable. Plasma cfDNA is sequenced; serum sIgA is measured optically. They meet only after independent QC.

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