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Pre-Analytical Errors in POCTPre-Analytical Errors in POCT

Felicity DempseyFelicity Dempsey

Biochemistry St James’s HospitalBiochemistry St James’s Hospital

Importance of Blood Gas AnalysisImportance of Blood Gas Analysis

““Blood Gas and pH analysis has more immediacy Blood Gas and pH analysis has more immediacy and potential impact on patient care than any other and potential impact on patient care than any other laboratory determination. In blood gas analysis, an laboratory determination. In blood gas analysis, an incorrect result can often be worse than no result at incorrect result can often be worse than no result at all.” all.”

NCCLS Document C27-A Approved guideline, April 1993NCCLS Document C27-A Approved guideline, April 1993

Pre-Analytical ErrorsPre-Analytical Errors

““Collection of a blood specimen, as well as its Collection of a blood specimen, as well as its handling and transport, are key factors in the handling and transport, are key factors in the accuracy of clinical laboratory analysis and accuracy of clinical laboratory analysis and ultimately in delivering quality patient care.”ultimately in delivering quality patient care.”

NCCLS Document H11-A Percutaneous collection of Arterial Blood for laboratory NCCLS Document H11-A Percutaneous collection of Arterial Blood for laboratory analysis: Approved Standard.analysis: Approved Standard.

Portability and SimplicityPortability and Simplicity Poor phlebotomy or collection techniquesPoor phlebotomy or collection techniques Lack of patient preparationLack of patient preparation Use of anti-coagulantsUse of anti-coagulants Transportation delaysTransportation delays Incorrect collection from I.V. linesIncorrect collection from I.V. lines Lack of training of usersLack of training of users

Pre analytical factors can introduce errors which are Pre analytical factors can introduce errors which are many times greater than the analytical imprecisions many times greater than the analytical imprecisions of the BGA. This can lead to incorrect decisions on of the BGA. This can lead to incorrect decisions on patient management being made.patient management being made.

Poor Phlebotomy and Collection techniquesPoor Phlebotomy and Collection techniques Arterial sample required.Arterial sample required. 5mls of blood discarded before ABG sample taken.5mls of blood discarded before ABG sample taken. Bubbles must be expelled.Bubbles must be expelled. Good quality heparin syringes required.Good quality heparin syringes required. Neddles removed and syringe capped immediatelyNeddles removed and syringe capped immediately Sample mixed by rolling horizontally for 15 seconds.Sample mixed by rolling horizontally for 15 seconds. Erroneous Hb, pH, pCoErroneous Hb, pH, pCo2 2 , Po, Po2 2 results occur when sample is not results occur when sample is not

appropriately mixed.appropriately mixed. Red cells settle out of the plasma rapidly, which effects the Hb, Red cells settle out of the plasma rapidly, which effects the Hb,

pH, pCopH, pCo2 2 and Po and Po2.2.

Lack of Patient PreparationLack of Patient Preparation

Two patient identifiers such as name and MRN must Two patient identifiers such as name and MRN must be used.be used.

Bar code identification should be used for both Bar code identification should be used for both patient and operator.patient and operator.

Better techniques for taking verbal or telephone Better techniques for taking verbal or telephone orders must be implemented.orders must be implemented.

Air Bubble in sampleAir Bubble in sample

A single air bubble in the A single air bubble in the sample will bias the Posample will bias the Po22 measurementsmeasurements

Comparisons of HaemoglobinsLab no Haem analyser Theatre Omni 9 KSICU Omni 9

Specimen 1Specimen 1 11.311.3 11.711.7 12.012.0






Use of Anti- CoagulantsUse of Anti- Coagulants Heparin is the preferred anti coagulant.Heparin is the preferred anti coagulant. Liquid heparin mixes easier with blood than dry heparin, but Liquid heparin mixes easier with blood than dry heparin, but

produces a dilution error.produces a dilution error. A dilution error of 5% in a 1ml blood sample will occur with a A dilution error of 5% in a 1ml blood sample will occur with a

heparin solution of 500-1000 IU/ml.heparin solution of 500-1000 IU/ml. Different heparin preparations contain various amounts of Different heparin preparations contain various amounts of

CaCa++, K, K++ and Na and Na++ which may increase measured values. which may increase measured values. Where possible use purpose made syringes containing the Where possible use purpose made syringes containing the

correct amount of heparincorrect amount of heparin..

Transportation DelaysTransportation Delays Ideally ABG measurements should be carried out Ideally ABG measurements should be carried out

immediately, as cell metabolism continues in the syringe immediately, as cell metabolism continues in the syringe after collection.after collection.

This causes an increase in plasma KThis causes an increase in plasma K++ and a decrease in and a decrease in pCopCo22, pH and pO, pH and pO22

If specimen is kept at R.T it should be analysed in 10 mins.If specimen is kept at R.T it should be analysed in 10 mins. ABG sample may be stored at 0-4ABG sample may be stored at 0-4ooC in iced water for 30-40 C in iced water for 30-40

mins before analysis.mins before analysis. Longer storage is not recommended.Longer storage is not recommended. Plasma KPlasma K++ rises during cold storage. rises during cold storage.

Training of UsersTraining of Users Getting accurate results for critical parameters when and Getting accurate results for critical parameters when and

where needed depends on the skill of the operator.where needed depends on the skill of the operator. Training in the collection, transportation and storage of ABG Training in the collection, transportation and storage of ABG

is vital.is vital. Training in the technical and operational factors are also of Training in the technical and operational factors are also of

great importance.great importance. Convenience of POCT can produce poor quality of results Convenience of POCT can produce poor quality of results

and lead to over utilization of the analyser.and lead to over utilization of the analyser.

All users should be trained by a designated trainer.All users should be trained by a designated trainer. Users should sign off on various stages of carrying out Users should sign off on various stages of carrying out

the procedure, records should be left for reference.the procedure, records should be left for reference. Training must be standardised so that all users receive Training must be standardised so that all users receive

the same information.the same information. Standardised training and frequent checks of operator Standardised training and frequent checks of operator

competency demonstrates the most significant level of competency demonstrates the most significant level of performance improvement.performance improvement.

Blood Gas analysis is not a “black box”Blood Gas analysis is not a “black box”

It is a well It is a well described process described process with a set of distinct with a set of distinct phases that must phases that must be performed with be performed with care and attentioncare and attention..In

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