The next critical stage of the transfusion process is blood sampling for pre-transfusion testing. Two general types of errors are usually reported in most HV system: mislabeled samples, where the label has errors, and miscollected samples, where the blood in the tube is not that of the patient whose name is on the label. Miscollected samples are also called wrong blood in tube (WBIT). A miscollected sample represents a greater risk. The rate of detected WBITs underestimates the true rate of miscollected samples because a miscollected sample may, by chance, match the blood group results on record for the patient named on the tube. A WBIT sample in an otherwise properly labeled tube represents a serious error, because the sample will be used by the laboratory for pretransfusion testing. WBIT samples where no previous blood group result for the patient is on record are a particular concern if the blood in the sample is not compatible with the true blood group of the individual named on the tube because blood products correctly crossmatched and correctly tagged using this sample will be incompatible with the recipient’s blood. Evidence supports the concept that mislabeling of blood samples is associated with actual WBIT events. Indeed, Lumadue and colleagues(87) have shown that a WBIT sample is 40-fold more likely to be found in a specimen that is also mislabelled.
The frequency of samples in which the blood group differed from that obtained previously (wrong blood in tube) was assessed in an international study of nearly 700 000 samples in 10 countries done by ISBT working party (afterwards by Biomedical Excellence for Safer Transfusion group). The median rate of wrong blood in tube, similar across nearly all of the participating countries, was approximately 1:2000. Comparable rates were found in a national study in England (89). Practices resulting in ‘wrong blood in tube’ include labelling of sample tubes away from the bedside, failure to check patient identity and the use of preprinted labels, which are proscribed by the British Committee for Standards in Haematology Guidelines on Administration of Blood and Blood Components. Banning of preprinted labels results in a higher rate of samples rejected due to minor discrepancies, but a reduction in the incidence of ‘wrong blood in tube(88).
Poor techniques in blood sampling for diagnostic investigations may also give rise to inappropriate transfusion, sometimes with clinically significant consequences.
The UK Serious Hazards of Transfusion (SHOT) reported cases wherein blood was taken from a ‘‘drip arm,’’ resulting in an erroneous haemoglobin values and an inappropriate decision to transfuse contributed to the deaths of two patients (66).
To reduce the risk of sampling errors, all staff undertaking phlebotomy must receive training and competence assessment. Hospital policies should state that blood samples must be taken from a free flowing venipuncture site, the tube filled to capacity and adequately mixed. The phlebotomist must complete the tube label before leaving the patient, checking that the identification details are correct verbally with the patient and against the identification wristband or equivalent.