CPD Plasma vs. Citrate Plasma: Key Differences Explained
CPD and citrate plasma are both anticoagulated with citrate — but they are not the same matrix. The additional components in CPD solution introduce measurable differences in plasma composition that matter for IVD validation, immunoassay development, and DMPK protein binding studies. Here is a clear breakdown.
What Is CPD Plasma?
CPD plasma is collected using Anticoagulant Citrate Phosphate Dextrose (CPD) solution — a mixture of four components in fixed proportions: sodium citrate (anticoagulant), citric acid (pH buffer), monobasic sodium phosphate (buffer and stabiliser), and dextrose (glucose, for red cell preservation during whole blood storage). The CPD solution is present at a 1:7 ratio to whole blood volume in standard collection bags.
After centrifugation of the whole blood unit, the cellular fraction is removed and the remaining plasma — now containing CPD anticoagulant — is collected. This is CPD plasma.
What Is Citrate Plasma?
Citrate plasma is anticoagulated with sodium citrate only — typically at 3.2% (0.109 mol/L) or 3.8% (0.129 mol/L), added to whole blood or collected via apheresis at a 1:9 citrate:blood ratio. No phosphate, no dextrose. The citrate chelates calcium ions, preventing coagulation cascade activation, while leaving plasma composition otherwise unmodified.
Citrate plasma is the standard anticoagulant for coagulation testing (PT, APTT, fibrinogen, factor activity assays) and is widely used in DMPK protein binding assays and IVD validation as a cleaner alternative to CPD.
Side-by-Side Comparison
| Parameter | CPD Plasma | Sodium Citrate Plasma (3.2%/3.8%) |
|---|---|---|
| Antikoagulans | Sodium citrate + citric acid + NaH₂PO₄ + dextrose | Sodium citrate only |
| Anticoagulant:blood ratio | 1:7 (fixed by bag volume) | 1:9 (standard for 3.2%) |
| Glucose level in plasma | Elevated ~20–25 mM above physiological level (from dextrose) | Physiological — no added glucose |
| Phosphate content | Elevated — additional inorganic phosphate from NaH₂PO₄ | Physiological — no additional phosphate |
| Freies Kalzium | Chelated by citrate — not available for coagulation | Chelated by citrate — reversible by adding CaCl₂ |
| Protein composition | Physiological — all plasma proteins present | Physiological — all plasma proteins present |
| Coagulation factors | Preserved if frozen rapidly | Preserved; preferred format for coagulation assays |
| Collection route | Whole blood donation only | Whole blood or apheresis |
| Glucose-sensitive assays | Not suitable — elevated glucose artefact | Geeignet |
| Phosphate-sensitive assays | Potential interference — check assay dependency | No concern |
| DMPK protein binding assays | Usable but dextrose can affect drug partitioning in some systems | Preferred — cleaner matrix |
| IVD calibrator / control matrix | Historically used; supply is declining | Current best-practice alternative |
| Supply outlook (EU) | Tightening — structural decline | Stable and growing with apheresis |
The Dextrose Issue: Why It Matters More Than It Sounds
The dextrose in CPD solution adds approximately 20–25 mmol/L of glucose to the plasma matrix above the normal physiological range (approximately 4–6 mmol/L fasting). This elevated glucose level is invisible on a standard CoA — it is not reported as an anomaly because it is an expected feature of the CPD matrix, not a quality failure.
For most immunoassay and haematology applications, this glucose elevation is irrelevant. But for specific assay types, it is a significant matrix interference:
Glucose assays
Any assay measuring plasma glucose — clinical chemistry glucose methods, glucose oxidase-based ELISA — will return artificially high values in CPD plasma. CPD plasma cannot be used as a calibrator or control matrix for glucose measurement.
Enzyme activity assays
Some enzymes involved in glycolysis or phosphate metabolism show altered activity in the elevated glucose/phosphate environment of CPD plasma. If your assay measures enzyme activity directly, validate the matrix effect specifically.
DMPK plasma protein binding (PPB)
In plasma protein binding studies using equilibrium dialysis or rapid equilibrium dialysis (RED assay), the elevated glucose and phosphate in CPD plasma can subtly alter the osmotic environment and potentially affect drug-protein binding equilibria for compounds with narrow binding constants. Citrate plasma is the cleaner matrix for PPB work.
When CPD, When Citrate — Quick Reference
| Anwendung | Recommended Matrix | Grund |
|---|---|---|
| General immunoassay validation (troponin, CRP, ferritin, hormones) | Citrat-Plasma | Cleaner matrix; no glucose or phosphate artefact; better supply |
| Coagulation assays (PT, APTT, fibrinogen, factor activity) | Citrate plasma 3.2% | Industry and regulatory standard; calcium reversibility required |
| DMPK plasma protein binding | Citrat-Plasma | Physiological matrix; avoids glucose interference |
| Glucose or glycaemic assay validation | Not CPD — use citrate or EDTA | CPD dextrose invalidates glucose measurement |
| IVD calibrator manufacturing (large bulk lots) | Apheresis citrate plasma | Larger individual lot volumes, better consistency, stable supply |
| Haematology method validation (where plasma is the matrix) | Either — validate per method | Check anticoagulant interference with specific analyte |
Citrate Plasma (3.2% / 3.8%) — EU Origin, Available Now
Pooled and single-donor sodium citrate plasma, apheresis volumes and ACD-A format — from certified EU donor centres, shipped from Germany. Full CoA per lot. No minimum order quantity.
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