# Blood Collection Tubes Comparison Guide – EDTA, Clot Activator, Fluoride, Citrate, ESR & Lithium Heparin Tubes

**By Microsidd India** · 2026-08-05

# Blood Collection Tubes Comparison – Complete Guide to EDTA, Clot Activator, Fluoride, Citrate, ESR & Lithium Heparin Tubes

## Introduction

Selecting the correct blood collection tube is essential for obtaining reliable laboratory test results. Each tube contains a specific additive or anticoagulant designed for particular diagnostic applications. Using the wrong tube can affect specimen quality, interfere with laboratory analysis, or require repeat sample collection.

This comprehensive comparison explains the differences between the most commonly used blood collection tubes:

-   Purple Cap (EDTA)
-   Red Cap (Clot Activator)
-   Grey Cap (Fluoride)
-   Sky Blue Cap (Sodium Citrate)
-   Black Cap (ESR)
-   Green Cap (Lithium Heparin)

Whether you are a laboratory professional, hospital, diagnostic centre, nursing student, or healthcare provider, this guide will help you choose the appropriate tube for each investigation.

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# Quick Comparison Table

Tube Type

Cap Colour

Additive

Sample Type

Common Tests

EDTA Tube

🟣 Purple

K2/K3 EDTA

Whole Blood

CBC, HbA1c, Blood Grouping

Clot Activator Tube

🔴 Red

Clot Activator

Serum

LFT, KFT, Thyroid, Lipid Profile

Fluoride Tube

⚪ Grey

Sodium Fluoride + Potassium Oxalate

Plasma

Blood Glucose, GTT

Citrate Tube

🔵 Sky Blue

3.2% Sodium Citrate

Plasma

PT, INR, APTT, Coagulation Studies

ESR Tube

⚫ Black

Sodium Citrate

Whole Blood

ESR

Lithium Heparin Tube

🟢 Green

Lithium Heparin

Plasma

Electrolytes, Cardiac Markers, Emergency Chemistry

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# Detailed Tube Comparison

## 1\. EDTA Blood Collection Tube (Purple Cap)

### Purpose

EDTA prevents blood clotting by binding calcium, preserving blood cells for hematology testing.

### Common Tests

-   Complete Blood Count (CBC)
-   Hemoglobin (Hb)
-   HbA1c
-   Blood Grouping
-   Peripheral Smear
-   Malaria Parasite Examination
-   Reticulocyte Count

### Advantages

-   Excellent preservation of blood cell morphology
-   Suitable for automated hematology analyzers
-   Prevents clot formation
-   Stable blood cells

### Specifications

-   Cap Colour: Purple/Lavender
-   Additive: K2 EDTA or K3 EDTA
-   Sample: Whole Blood
-   Mixing: 8–10 gentle inversions

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## 2\. Clot Activator Tube (Red Cap)

### Purpose

Contains clot activator particles that accelerate clot formation for serum separation.

### Common Tests

-   Liver Function Test (LFT)
-   Kidney Function Test (KFT)
-   Thyroid Profile
-   Lipid Profile
-   Vitamin D
-   Hormone Assays
-   Tumor Markers
-   Serology

### Advantages

-   Faster clotting
-   Clear serum separation
-   Suitable for routine biochemistry
-   High-quality serum samples

### Specifications

-   Cap Colour: Red
-   Additive: Silica Clot Activator
-   Sample: Serum
-   Clotting Time: Approximately 20–30 minutes

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## 3\. Fluoride Blood Collection Tube (Grey Cap)

### Purpose

Fluoride inhibits glycolysis, preserving blood glucose levels after collection.

### Common Tests

-   Blood Sugar
-   Fasting Blood Glucose
-   Postprandial Blood Sugar
-   Glucose Tolerance Test (GTT)
-   Lactate (where validated)

### Advantages

-   Prevents glucose degradation
-   Improves accuracy of glucose measurements
-   Suitable for diabetes investigations

### Specifications

-   Cap Colour: Grey
-   Additive: Sodium Fluoride + Potassium Oxalate
-   Sample: Plasma
-   Mix immediately after collection

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## 4\. Sodium Citrate Tube (Sky Blue Cap)

### Purpose

Specially designed for coagulation studies by preserving clotting factors.

### Common Tests

-   PT
-   INR
-   APTT
-   D-Dimer
-   Fibrinogen
-   Coagulation Factor Assays

### Advantages

-   Maintains coagulation factors
-   Standard tube for coagulation laboratories
-   Highly accurate clotting studies

### Specifications

-   Cap Colour: Sky Blue
-   Additive: 3.2% Sodium Citrate
-   Sample: Plasma
-   Fill tube completely to maintain the required blood-to-additive ratio

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## 5\. ESR Tube (Black Cap)

### Purpose

Designed specifically for Erythrocyte Sedimentation Rate (ESR) testing.

### Common Tests

-   ESR

### Advantages

-   Accurate sedimentation testing
-   Standardized anticoagulant concentration
-   Reliable inflammatory marker assessment

### Specifications

-   Cap Colour: Black
-   Additive: Sodium Citrate
-   Sample: Whole Blood
-   Used for Westergren ESR method where applicable

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## 6\. Lithium Heparin Tube (Green Cap)

### Purpose

Lithium Heparin prevents clotting while allowing rapid plasma testing.

### Common Tests

-   Electrolytes
-   Cardiac Enzymes
-   Troponin
-   Renal Function
-   Liver Function
-   Emergency Chemistry
-   Plasma Biochemistry

### Advantages

-   Rapid plasma separation
-   Suitable for emergency laboratories
-   Minimal interference in many chemistry assays

### Specifications

-   Cap Colour: Green
-   Additive: Lithium Heparin
-   Sample: Plasma
-   Mix gently after collection

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# Comprehensive Comparison Table

Feature

EDTA (Purple)

Clot Activator (Red)

Fluoride (Grey)

Citrate (Sky Blue)

ESR (Black)

Lithium Heparin (Green)

Sample Type

Whole Blood

Serum

Plasma

Plasma

Whole Blood

Plasma

Prevents Clotting

✔

✖

✔

✔

✔

✔

Produces Serum

✖

✔

✖

✖

✖

✖

Produces Plasma

✖

✖

✔

✔

✖

✔

Hematology

⭐⭐⭐⭐⭐

✖

✖

✖

✔

✖

Biochemistry

✖

⭐⭐⭐⭐⭐

✔

✖

✖

⭐⭐⭐⭐

Coagulation

✖

✖

✖

⭐⭐⭐⭐⭐

✖

✖

Blood Glucose

✖

✖

⭐⭐⭐⭐⭐

✖

✖

✖

ESR

✖

✖

✖

✖

⭐⭐⭐⭐⭐

✖

Emergency Testing

✖

✔

✔

✔

✖

⭐⭐⭐⭐⭐

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# Order of Draw (Recommended)

To minimize additive carryover during venipuncture, a commonly recommended order of draw is:

1.  Blood Culture Bottles (if required)
2.  Sky Blue (Citrate)
3.  Red (Clot Activator)
4.  Green (Lithium Heparin)
5.  Purple (EDTA)
6.  Grey (Fluoride)

Always follow your laboratory's validated procedures and applicable guidelines.

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# Frequently Asked Questions

### Why are blood collection tubes colour coded?

The cap colour identifies the additive inside the tube, helping healthcare professionals select the correct tube for each laboratory investigation.

### Can I use an EDTA tube for blood glucose testing?

No. A grey fluoride tube is generally recommended for glucose testing because it helps preserve glucose levels after collection.

### Why must citrate tubes be filled completely?

The anticoagulant-to-blood ratio is critical for accurate coagulation testing. Underfilled tubes can produce unreliable PT, INR, or APTT results.

### Which tube is best for CBC?

A purple cap EDTA tube is the standard choice for Complete Blood Count (CBC).

### Which tube is used for liver function tests?

A red clot activator tube is commonly used to obtain serum for liver function testing.

### Which tube is used for ESR?

A black cap ESR tube is designed specifically for erythrocyte sedimentation rate testing.

### Why is a green tube used in emergency laboratories?

Lithium Heparin tubes provide plasma quickly without waiting for clot formation, making them useful for many urgent chemistry investigations.

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# Why Buy Blood Collection Tubes from Microsidd?

-   Genuine laboratory-quality blood collection tubes
-   Suitable for hospitals, diagnostic laboratories, research centres, and educational institutions
-   Reliable vacuum performance for consistent specimen collection
-   Secure packaging to reduce transit damage
-   Competitive pricing for bulk and institutional purchases
-   Fast dispatch across India
-   GST invoices available for business and institutional orders
-   Trusted supplier with extensive experience in IVD and laboratory consumables

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> Source: [Microsidd India](https://microsidd.com/blogs/knowledge-hub/blood-collection-tubes-comparison)