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Who this is for: clinic and laboratory staff, buyers and students who need to tell what a heparinized syringe is, how dry and liquid heparin differ, and why fill volume matters for blood gas results. This page describes products and general use; it is not medical advice.
What a heparinized syringe is
A heparinized syringe is a syringe that contains heparin, an anticoagulant, so that a blood sample drawn into it does not clot before analysis. It is most often associated with arterial blood gas (ABG) sampling, where a clotted or diluted sample gives unreliable results.
Who uses it: clinicians and laboratory staff who collect samples for blood gas and electrolyte analysis, and the buyers and supply managers who stock those syringes.
How it is built: dry heparin versus liquid heparin
There are two ways the heparin gets into the syringe, and they behave differently.
- Dry (dried, balanced) heparin. A commercial, preweighed amount of heparin is dried onto the syringe. Chhapola and colleagues (2014) describe it as electrolyte-balanced; Lobo (2014) explains that the balancing uses lithium and zinc rather than sodium or calcium.
- Liquid heparin. The syringe is prepared in-house: liquid heparin is drawn in and expelled so that a thin film coats the wall (Chhapola et al., 2014). Whatever remains in the syringe and needle dead space mixes with the sample.
Kume and colleagues (2012) separate the liquid-heparin error into two mechanisms. The dilutional effect is the percentage by which the sample is diluted. The chemical effect is the final heparin concentration in the sample. Both depend on how much heparin is retained in the dead space. Lobo (2014) adds that liquid heparin dilutes the plasma and that low sodium, potassium and calcium results have previously been attributed to liquid heparin binding cations in the sample.
Types and variants
| Type | Typical use | Key difference | Source |
|---|---|---|---|
| Dry balanced heparin syringe | Blood gas and electrolyte sampling | Commercial, preweighed, electrolyte-balanced using lithium and zinc; no liquid to dilute the sample | Lobo 2014; Chhapola et al. 2014 |
| Liquid heparin-washed syringe | Blood gas sampling where syringes are prepared in-house | Heparin is aspirated and expelled to coat the wall; retained liquid dilutes the sample and has been linked to cation binding | Chhapola et al. 2014; Kume et al. 2012; Lobo 2014 |
Why syringe size and fill volume matter
Kume and colleagues (2012) measured liquid-heparin dilution in plastic syringes (1, 2, 5 and 10 mL; 20G to 26G needles; seven volunteers). The smaller the syringe, the larger the needle and the less blood drawn, the more the sample was diluted.
| Condition (liquid-heparin-washed syringe) | Dilution | Final heparin concentration |
|---|---|---|
| 10 mL syringe, filled | 2.0% | 100 IU/mL |
| 1 mL syringe | 7.0% | 351 IU/mL |
| 1 mL syringe with 26G needle | 4.9% | 245 IU/mL |
| 1 mL syringe with 20G needle | 7.6% | 380 IU/mL |
| 0.5 mL drawn into a 10 mL syringe (underfilled) | 34% | 1675 IU/mL |
In the underfilled case, changes in pCO2, sodium, potassium and ionized calcium exceeded the acceptable limits the authors applied; ionized calcium and magnesium fell and sodium rose. The pH difference was not significant (P = 0.128) and pO2 stayed acceptable. These figures come from one study of liquid-heparin syringes and do not describe dry-heparin products.
Dry and liquid heparin are not interchangeable
Paired-sample studies found that results from the two methods do not match closely enough to be treated as the same.
| Finding | Source |
|---|---|
| In a paired study discussed by Lobo, the mean pH values (7.42 and 7.41) differed significantly but no individual pH value exceeded the total allowable error. About 40% of pCO2 values fell outside allowable error, and sodium, potassium, chloride and bicarbonate varied widely. The editorial concludes the two methods are not comparable. | Lobo 2014 |
| In 35 paediatric ICU patients, liquid heparin showed a slight negative mean bias against dry balanced heparin for pH, pCO2, bicarbonate, pO2, potassium, sodium, chloride and lactate. pH and lactate agreed best; sodium agreed worst, with 27 of 35 pairs (77%) exceeding total allowable error. | Chhapola et al. 2014 |
How to choose
The published sources state two criteria.
- Dry, electrolyte-balanced heparin. Kume and colleagues conclude that, to prevent serious errors from nonstandardized blood gas sampling, electrolyte-balanced dry heparin may be recommended. They note that liquid heparin remains in use for economic and traditional reasons; Lobo (2014) says cost should not compromise accuracy.
Kume and colleagues also note that the CLSI guidelines did not describe a collection procedure for liquid-heparin-washed syringes, although it warned of the combined dilutional and chemical effects. The current edition, CLSI C46, second edition (2009), consolidates six earlier CLSI documents and covers terminology, performance characteristics, preanalytical variables, analytical considerations and quality control for in vitro blood gas and pH analysis.
Safe use and handling basics
Sample handling before analysis is a major source of error. Lobo (2014) cites an estimate that preanalytical handling accounts for 75% of the errors in blood gas analysis. The main lesson concerns preparation and volume: the heparin form and the amount of blood collected both change the result. Collection technique is set by facility protocol and the product instructions for use, which this page does not replace.
Common mistakes
- Underfilling a liquid-heparin syringe. A 0.5 mL sample in a 10 mL syringe was diluted by 34% in the Kume study (table above).
- Comparing dry and liquid heparin results as if they were one method. The paired studies above found they are not comparable for several analytes.
- Non-standardized in-house preparation. In Kume and colleagues’ non-standardized clinical sampling, results exceeded limits for pCO2 in 47%, sodium in 80%, potassium in 99% and ionized calcium in 100% of cases.
- Treating a heparin tube as a syringe. Tube anticoagulants are a different product class; see blood draw tube colors and the green top tube.
Related reading
Blood gas samples feed analysers such as co-oximeters (co-oximetry), may come from an indwelling line (arterial line tubing), and differ from capillary blood collection.
FAQ
What is a heparinized syringe?
A syringe that contains heparin, an anticoagulant, so a blood sample drawn into it does not clot before analysis, most often for arterial blood gas sampling.
What is the difference between dry and liquid heparin?
Dry heparin is a commercial, preweighed, electrolyte-balanced amount dried onto the syringe. Liquid heparin is prepared in-house and coats the wall as a thin film; heparin retained in the dead space can dilute the sample (Chhapola et al., 2014; Kume et al., 2012).
Can dry and liquid heparin results be compared directly?
Lobo (2014) concluded that values from the two techniques are not comparable, and a paediatric ICU study found sodium differences beyond total allowable error in 27 of 35 pairs.
Why does syringe size matter?
In liquid-heparin-washed syringes, smaller syringes and larger needles gave more dilution (Kume et al., 2012; see the table above).
Sources
- Lobo V. To heparinize or not to heparinize: effect on arterial blood gas measurements. Indian J Crit Care Med 2014;18(1):1-2. https://pmc.ncbi.nlm.nih.gov/articles/PMC3912661 (checked 2026-11-01).
- Kume T, Sisman AR, Solak A, Tuglu B, Cinkooglu B, Coker C. The effects of different syringe volume, needle size and sample volume on blood gas analysis in syringes washed with heparin. Biochem Med 2012;22(2):189-201. https://www.biochemia-medica.com/en/journal/22/2/10.11613/BM.2012.022/fullArticle (checked 2026-11-01).
- Chhapola V, Kumar S, Goyal P. Indian J Crit Care Med 2014;18(1):14-19, as summarised at https://acutecaretesting.org/en/journal-scans/heparin-anticoagulation-of-samples-for-blood-gas-analysis (checked 2026-11-01).
- CLSI C46, Blood Gas and pH Analysis and Related Measurements, 2nd ed., 24 Feb 2009. https://clsi.org/shop/standards/c46/ (product page checked 2026-11-01).
