 13 hospitals from 4 regions of China (2 hospitals from the northeast region, 3 hospitals from the central region, 4 hospitals from the east region, and 4 hospitals from the west region), and 3077 valid questionnaires were returned, with an effective return rate of 90.5%. The demographic profile of the investigated nurses was shown in Table 1.
Almost all the investigated nurses were aware that patient identification should be confirmed prior to venous blood sampling. However, only 69.7% of the nurses knew what identifiers should be used for identifying a patient and 58.8% of the nurses knew the right procedures to identify a patient who is conscious. In addition, the correct rate of hand sanitization and patient assessment were no less than 95%. The detailed results on phlebotomy knowledge of the pre-sampling phase were shown in Table 2.
As Table 3 showed, the correct rates on the preferred vein for venipuncture, diameter of disinfec-tion, proper time and approach for mixing tubes were relatively high (more than 85%). Although 78.1% of the nurses knew proper tourniquet application time, the correct rates on the tourniquet releasing time (18.5%) and tourniquet applying location (29.6%) were relatively low. The correct rate of tourniquet releasing time was associated with the regions of hospitals (P < 0.001), compared to the east region, the central region had the highest correct rate (odds ratio, OR = 0.68, 95% CI 0.51 -0.92), followed by northeast region (OR = 0.69, 95% CI 0.53 -0.91), while the west region had the lowest correct rate (OR = 1.32, 95% CI 1.02 -1.71) ( Table 4). In addition, around two thirds of the investigated nurses knew that gloves should be worn during phlebotomy, yet only about one third knew the proper time to put on gloves. Furthermore, only 15.5% of the nurses knew the right order of draw during multi-tube sampling (      * The right answer is 3 -red / yellow closure, 1 -blood culture tube, 5 -lavender closure, 4 -green closure, 2 -blue closure, 6 -gray closure.  Table 4). Regarding to the proper time to change tube during multi-tube sampling, the correct rate was 28.5%. Its correct rate was associated with the regions of hospitals (P < 0.001) and age of the nurses (P < 0.001), compared to the east region, the northeast region had a higher correct rate (OR = 0.24, 95% CI 0.19 -0.31); and the older the nurses, the higher the correct rate (OR = 0.96, 95% CI 0.94 -0.99) ( Table 4). As to the definition of an inversion, only 22.5% of the nurses knew the correct answer (Table 3). Its correct rate was associ-ated with regions of hospitals (P < 0.001) and departments of the nurses (P = 0.001), compared to the east region, the central region had the highest correct rate (OR = 0.49, 95% CI 0.37-0.65), followed by the northeast region (OR = 0.52, 95% CI 0.40 -0.68) and the west region (OR = 0.67, 95% CI 0.54 -0.85), while outpatient and emergency department (OR = 0.61, 95% CI 0.46 -0.82) had a higher correct rate compared to inpatient department ( Table 4). The knowledge of mix by inverting times for blood collection tubes was shown in Table 6. Among all the investigated nurses, 1012 failed to respond to this question, with a missing rate of 32.9%. As Table 6 showed, in four out of six tubes, the medians of responded times of tube inversions were lower than those of recommended times.   The correct rates on where to dispose needle, post-venipuncture education and tube labelling were relatively high (more than 85%). However, half of the investigated nurses considered the disposal of the needle after detaching the device with both hands acceptable practice. Around one quarter of the nurses stated that there was no need of documenting the time and person of blood collection. The detailed results on the phlebotomy knowledge in the post-sampling phase were shown in Table 7.

Discussion
To the best of our knowledge, few surveys were conducted on assessing the knowledge level of phlebotomy in Chinese nurses up to now. In addition, the surveys were conducted more than 5 years ago, and included only one or two hospitals, unable to provide a reliable reference for the overall situation of nurses' knowledge on phlebotomy at present (14,15). The level of knowledge on phlebotomy among Chinese nurses was found to be not quite satisfactory. Compared with previous survey in China, some progress had been made in the steps of patient preparation, tourniquet application time and test tube labeling, while the survey also showed that the mastery of some knowledge on venous blood sampling needed to be improved (14,15).
A high accuracy of patient identification is crucial to ensure patient safety, and a proper patient identification must rely on at least two independent identifiers. In our survey, the identifiers selected for identifying a patient include bed number (89.5%), and the approaches for identifying include nurses stating a patient's bed number. According to the CLSI H3-A6 guidelines and Joint Commission International requirements, bed number can't be used as an independent identifier for patient identification, due to the fact that it is not a unique index representing a patient (9,16). A misidentification could occur if judging only via the bed number and potentially causes serious consequences. Therefore, it is important to select the full name and patient identification number as the identifying variables.
The CLSI H3-A6 guidelines recommend that tourniquet application time should not exceed one minute and tourniquet should be released as soon as possible after the blood begins to flow to prevent spurious variation of several plasma analytes. The correct rate on tourniquet releasing time was low (18.5%) in our survey. A European survey showed that 43.0% of the nurses did not release the tourniquet when the first test tube had blood inflows (4). It is possible that nurses would not release tourniquet before the blood collection process is completed to avoid vein collapsing. Further studies are needed to explore whether this concern is evidence based or not.
Nonsterile gloves should be worn during sampling phase to prevent the spread of blood-borne pathogens among health-care professionals. As our investigation showed, nearly one third of the nurses were not aware of this requirement. A Kenyan survey showed that more than two-thirds of the nurses did not use a new pair of gloves in phlebotomy, while a European survey also found that more than half of the nurses did not wear gloves correctly during blood collection (4,5). Mbah considered this issue could be caused by a limited supply of gloves or a concern that a vein would not be able to feel with gloves on (17). We thought it was also possible that the nurses did not attach adequate importance on wearing gloves during sampling. Therefore, it is important to promote a routine use of gloves during blood sample collection.
A correct order of draw prevents the sample being contaminated by additives from previous tubes, which could cause an erroneous result. In fact, contamination of blood sample occurred frequently if the correct order of test tubes was not strictly followed (18). As our investigation showed, only a small proportion of the nurses (15.5%) were aware of the correct order of multi-tube blood sampling whereas most of the nurses (91.9%) in Europe knew the answer (4). One cause of the low correct rate among Chinese nurses on order of draw was related to the fact that no unified standard on order of draw existed in China, while the order taught in different textbooks varied widely (9,13). In addition, some studies have pointed out that an incorrect order of draw would not cause contamination when samples were taken under ideal phlebotomy conditions (19). However, other authors have argued that clinical blood collection was rarely carried out in an ideal condition and therefore it was recommended that phlebotomy should be executed in the order described in the CLSI H3-A6 guidelines (20). Furthermore, there are many types of vacuum tubes used in phlebotomy, thus it is not easy to keep the right combination order of the tubes in mind. To promote compli-ance with the right order of draw, we recommend the tube manufacturer to label the correct order of draw on the test tubes. Alternatively, the laboratory information system can be improved by adding the correct order of draw into the bar code of information printing system as a reminder.
Proper mixing is important for homogenizing the collected blood with the additives in the test tubes (12). An inversion means the test tube is inverted up and down for 180 degrees. As the survey showed, few nurses (22.5%) in China were aware of the correct definition of an inversion and the mix by inverting times for most tubes was below the standard. Giving that the Chinese nurses had a misunderstanding on the definition of an inversion, the actual mixing time might be even lower.
One study in Turkey showed that the correct rate of tube mixing after blood collection was 44.1%, while an observation study from Kenya also showed that nearly 90% of the sampling tubes were not properly mixed (5,7). Inadequate mixing of blood and anti-coagulations would increase the risk of blood coagulation. There was report showing that China had a high clot rate of rejected specimens for complete blood count testing (77.38%), which could possibly be caused by insufficient mixing (21). Therefore,