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Capillary Tubes for Micro-Hematocrit and Blood Collection

Capillary tubes are 75 mm thin-walled tubes (I.D. 1.15 mm, fill volume ~75 µL) that collect microvolume blood samples by capillary action for micro-hematocrit determination and microvolume sample transfer. Globe Scientific supplies soda lime glass tubes (plain blue tip; ammonium heparin green tip; sodium heparin red tip), unbreakable plastic formats for sharps-safety, and pre-calibrated borosilicate tubes for blood gas analyzers. All 75 mm formats fit standard hematocrit centrifuges rated to 14,500 RPM.

MBP stocks Globe Scientific capillary tube lines for clinical and research labs across the USA, Canada, and worldwide. Request a quote by contacting customerservice@mbpinc.net

Capillary Tubes

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What are Capillary Tubes?

Capillary tubes for laboratory use are thin-walled, open-ended tubes—typically 75 mm long with an internal diameter of 1.1–1.2 mm—that collect microvolume blood samples (40–80 µL) by capillary action from finger-stick or heel-stick punctures, directly from anticoagulated blood collection tubes, or from blood gas analyzers. They are the primary consumables for the micro-hematocrit (packed cell volume, PCV) determination: tubes are filled, sealed, centrifuged at 10,000–14,500 RPM for 5 minutes, and the ratio of packed red cells to total blood column is read against a hematocrit chart. Globe Scientific manufactures both soda lime glass and plastic (unbreakable) micro-hematocrit capillary tubes, as well as pre-calibrated borosilicate glass tubes for blood gas applications. Choose heparinized capillary tubes for direct finger-stick collection from untreated blood; choose plain (untreated) tubes when filling from an anticoagulated blood collection tube.

What you will find:

Glass capillary tubes for micro-volume liquid transfer
Heparinized capillary tubes for blood sample collection
Plain capillary tubes for general laboratory applications
Micro-hematocrit capillary tubes for blood analysis
Sealed-end and open-end capillary tubes for flexible workflows
Disposable precision-bore tubes for single-use sampling
Calibrated microcapillary tubes for consistent volume uptake
Thin-walled tubes for rapid capillary action filling
Sterile capillary tubes for diagnostic applications
General-purpose laboratory micro-sampling tubes

How to Choose Capillary Tubes

Plain vs. Heparinized
Plain capillary tubes (blue tip, Globe Scientific) are used when filling from a pre-anticoagulated specimen (EDTA or citrate blood collection tube). Heparinized tubes prevent clotting in samples collected directly from a skin puncture: ammonium heparin–coated tubes (green tip) and sodium heparin–coated tubes (red tip) are both available. The tip color is the universal identifier — confirm the coding convention with your supplier before ordering, as some manufacturers reverse the color assignments.

Glass vs. Plastic
Soda lime glass capillary tubes (Globe Scientific catalog 51602–51607) provide excellent capillary action, low surface adsorption, and superior optical clarity for reading the hematocrit column. Plastic capillary tubes (catalog 51620) eliminate the sharps hazard from glass breakage during centrifugation—a significant occupational safety consideration for high-volume clinical labs processing hundreds of hematocrit determinations daily. Both formats fit standard 75 mm hematocrit centrifuges.

Pre-Calibrated (Blood Gas) Tubes
Pre-calibrated borosilicate glass capillary tubes (Globe Scientific catalog 51628, I.D. 0.55 mm ± 0.03 mm) are precision-ground for blood gas and co-oximetry analyzers requiring specific internal volume tolerance. These differ from standard hematocrit tubes in inner diameter; using the wrong tube in a blood gas analyzer causes instrument error codes and inaccurate analyte results.

Centrifuge Compatibility
All 75 mm micro-hematocrit capillary tubes are compatible with standard hematocrit centrifuges rated for 10,000–14,500 RPM. Confirm your centrifuge head accepts the tube O.D. (1.5 mm ± 0.05 mm for Globe Scientific glass tubes) before ordering in bulk.

Compare Capillary Tube Types

Plain (Untreated): Soda lime glass material, blue tip color, 1.15 mm ± 0.05 mm I.D., used with anticoagulated blood collection tubes.
Ammonium Heparinized: Soda lime glass material, green tip color, 1.15 mm ± 0.05 mm I.D., used for direct finger-stick and general hematocrit applications.
Sodium Heparinized: Soda lime glass material, red tip color, 1.15 mm ± 0.05 mm I.D., used for direct finger-stick and pediatric applications.
Plain Plastic: Polypropylene material, blue tip color, 1.15 mm ± 0.05 mm I.D., used for sharps-safe hematocrit determination.
Pre-Calibrated (Blood Gas): Borosilicate glass material, tip color varies, 0.55 mm ± 0.03 mm I.D., used for blood gas analyzers and co-oximetry.

Specifications Context

Globe Scientific soda lime glass micro-hematocrit capillary tubes have an I.D. of 1.15 mm ± 0.05 mm, O.D. of 1.5 mm ± 0.05 mm, and a length of 75 mm ± 1 mm, with a fill volume of approximately 75 µL. The standard centrifugation protocol is 10,000–14,500 RPM for 5 minutes in a dedicated hematocrit centrifuge. Normal hematocrit ranges: 38–50% for adult males, 35–47% for adult females; values outside this range, combined with elevated ESR and other CBC parameters, are used to evaluate anemia, polycythemia, and inflammatory conditions. As of 2026, Globe Scientific is an ISO 9001:2015–certified manufacturer and MBP-stocked supplier of both glass and plastic capillary tube formats.

For specifications, size options, or bulk ordering support, connect with the MBP team to choose the right capillary solution for your laboratory application.

FAQ

Capillary tubes are 75 mm thin-walled tubes that collect 40–80 µL of blood by capillary action for micro-hematocrit (packed cell volume) determination: tubes are filled, sealed, centrifuged at 10,000–14,500 RPM for 5 minutes, and the packed red cell column is measured against a hematocrit chart. They are also used in blood gas collection, newborn screening, and microvolume sample transfer workflows.

Plain capillary tubes (blue tip) contain no anticoagulant and are used when filling from a pre-anticoagulated blood collection tube (EDTA or citrate). Heparinized capillary tubes—ammonium heparin (green tip) or sodium heparin (red tip)—prevent clotting when collecting blood directly from a finger-stick or heel-stick. Using a plain tube for direct capillary collection causes clot formation and inaccurate hematocrit results.

Plastic capillary tubes (polypropylene) eliminate the sharps hazard from glass breakage during centrifugation and handling, making them the preferred choice for high-volume clinical settings where occupational safety is a priority. Glass capillary tubes provide superior optical clarity for reading the packed cell column and better capillary action; they remain common in research settings where throughput is lower and the centrifuge is enclosed.

Standard micro-hematocrit capillary tubes are centrifuged at 10,000–14,500 RPM for 5 minutes in a dedicated hematocrit centrifuge. Centrifuge speed below 10,000 RPM results in incomplete packing of red blood cells and falsely elevated hematocrit readings. The centrifuge head must accommodate 75 mm tubes with an O.D. of 1.5 mm ± 0.05 mm; confirm tube dimensional compatibility with your centrifuge model before ordering.

Standard micro-hematocrit tubes have an I.D. of 1.15 mm ± 0.05 mm and a fill volume of approximately 75 µL, designed for hematocrit centrifugation. Pre-calibrated borosilicate glass blood gas tubes (Globe Scientific catalog 51628) have a tighter I.D. of 0.55 mm ± 0.03 mm to meet the specific fill-volume tolerance required by blood gas and co-oximetry analyzers. Using a standard hematocrit tube in a blood gas instrument causes volume errors and instrument alarms.

Globe Scientific color-coding: blue tip = plain (untreated); green tip = ammonium heparin–coated; red tip = sodium heparin–coated. This convention is widely adopted but not universal — some manufacturers use different color assignments. Always confirm the color-coding scheme with the specific manufacturer's datasheet before using color alone to identify tube anticoagulant status in a clinical workflow.

Globe Scientific micro-hematocrit capillary tubes are typically supplied in packs of 200 tubes with sealing clay, or in bulk packs of 500 or 1,000. MBP offers direct case-quantity ordering by purchase order for clinical labs managing high-volume hematocrit testing programs across multiple draw stations.

Globe Scientific glass capillary tubes (75 mm × 1.5 mm O.D.) and plastic capillary tubes (same external dimensions) are compatible with standard 75 mm hematocrit centrifuges including those from Haematospin, Drucker Diagnostics, and Hawksley. Confirm your centrifuge head accepts the specific O.D. and tube count per rotor before placing a bulk order.

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