Effects of preanalytical factors on the intraindividual variation of analytes in the blood of healthy subjects: consideration of preparation of the subject and time of venipuncture

The preanalytical phase – from an instrument-centred to a patient-centred laboratory medicine

In order to guarantee patient safety, medical laboratories around the world strive to provide highest quality in the shortest amount of time. A major leap in quality improvement was achieved by aiming to avoid preanalytical errors within the total testing process. Although these errors were first described in the 1970s, it took additional years/decades for large-scale efforts, aiming to improve preanalytical quality by standardisation and/or harmonisation. Initially these initiatives were mostly on the local or national level. Aiming to fill this void, in 2011 the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) working group “Preanalytical Phase” (WG-PRE) was founded. In the 11 years of its existence this group was able to provide several recommendations on various preanalytical topics. One major achievement of the WG-PRE was the development of an European consensus guideline on venous blood collection. In recent years the definition of the preanalytical phase has been extended, including laboratory test selection, thereby opening a huge field for improvement, by implementing strategies to overcome misuse of laboratory testing, ideally with the support of artificial intelligence models. In this narrative review, we discuss important aspects and milestones in the endeavour of preanalytical process improvement, which would not have been possible without the support of the Clinical Chemistry and Laboratory Medicine (CCLM) journal, which was one of the first scientific journals recognising the importance of the preanalytical phase and its impact on laboratory testing quality and ultimately patient safety.

Haematological and Biochemical Reference Values for Healthy Population of Maferinyah Rural Community in Guinea

Guinea's reference ranges for biological parameters rely on those of Caucasian values. Variability in reference ranges according to the context is well-documented. We conducted this study for the purpose of future malaria clinical trials that assess the efficacy and safety of malaria drugs. A repeated cross-sectional study was carried out, in an apparently healthy cohort population. Surveys took place in Maferinyah rural community, which is located at 75 km from the capital. The 2.5^th and 97.5^th percentiles were determined nonparametrically and stood for reference intervals. Reference values were determined separately for males and females according to ranges of age (6-10 years of age; 11-15 years of age; 16-45 years of age). Differences between genders were tested using the Mann-Whitney test, while the Friedman test was performed to test differences within each gender group according to the seasons. A total of 450 volunteers were enrolled. The median age was 13. Males 16-45 years of age had significantly higher hematologic and biochemical values compared to a female of the same age (for hematological parameters: Mean Cell Hemoglobin Concentration MCHC p ≤ 0.001, Platelets p ≤ 0.001, monocytes p = 0.0305, eosinophils p = 0.0225; for biochemical parameters: Aspartate aminotransferase AST p ≤ 0.001, Alanine Aminotransferase ALT p ≤ 0.001, creatinine p ≤ 0.001). We noticed significant seasonal variations for all the biochemical parameters and some hematologic parameters (Mean Corpuscular Hemoglobin MCH, MCHC, Mean Cell volume). This is the first study establishing hematologic and biochemical parameters in Guinea. These findings provide a useful guide for the clinical researchers and care providers. Studies on large scale and in different settings would be also desirable.

Preanalytical Phase Errors: Experience of a Central Laboratory

Introduction: The study intends to observe the frequency of preanalytical phase errors both inside and outside the clinical laboratory according to certain quality indicators (QIs).

Methods: The one-week observation focused on 73 nurses drawing blood from 337 patients. It was performed in two stages: the observation of blood collection up to the receipt of the samples, and the receipt of the samples up to the analytical phase. The data pertaining to the number of patients, tests, and rejection rates were obtained from the laboratory information system (LIS) for the one-week and the one-year period and compared with the observational data.

Results: The process of blood sample collection from 337 patients taken into 1347 tubes was observed. Although the majority of the nurses (78%) used safety needles, the safety mechanism was properly activated only in 38% of the interventions. Evaluation of biochemistry tubes (n=971) revealed the following: the incorrect fill volume error was 40%; the hemolysis was seen by 17%, and the clotted sample and fibrin were observed by 6%. The incorrect fill volume error was 12% and 20% in ethylenediaminetetraacetic acid (EDTA) and citrated tubes, respectively. Clotted samples and platelet clumps were seen in 1% of EDTA tubes.

Conclusion: The study confirms the relative frequency of preanalytical phase error occurring inside and outside of the laboratory.

Quality Assurance in Clinical Chemistry: A Touch of Statistics and A Lot of Common Sense

Working in laboratories of clinical chemistry, we risk feeling that our personal contribution to quality is small and that statistical models and manufacturers play the major roles. It is seldom sufficiently acknowledged that personal knowledge, skills and common sense are crucial for quality assurance in the interest of patients. The employees, environment and procedures inherent to the laboratory including its interactions with the clients are crucial for the overall result of the total testing chain. As the measurement systems, reagents and procedures are gradually improved, work on the preanalytical, postanalytical and clinical phases is likely to pay the most substantial dividends in accomplishing further quality improvements. This means changing attitudes and behaviour, especially of the users of the laboratory. It requires understanding people and how to engage them in joint improvement processes. We need to use our knowledge and common sense expanded with new skills e.g. from the humanities, management, business and change sciences in order to bring this about together with the users of the laboratory.

The role of European Federation of Clinical Chemistry and Laboratory Medicine Working Group for Preanalytical Phase in standardization and harmonization of the preanalytical phase in Europe

Patient safety is a leading challenge in healthcare and from the laboratory perspective it is now well established that preanalytical errors are the major contributor to the overall rate of diagnostic and therapeutic errors. To address this, the European Federation of Clinical Chemistry and Laboratory Medicine Working Group for Preanalytical Phase (EFLM WG-PRE) was established to lead in standardization and harmonization of preanalytical policies and practices at a European level. One of the key activities of the WG-PRE is the organization of the biennial EFLM-BD conference on the preanalytical phase to provide a forum for National Societies (NS) to discuss their issues. Since 2012, a year after the first Preanalytical phase conference, there has been a rapid growth in the number of NS with a working group engaged in preanalytical phase activities and there are now at least 19 countries that have one. As a result of discussions with NS at the third conference held in March 2015 five key areas were identified as requiring harmonisation. These were test ordering, sample transport and storage, patient preparation, sampling procedures and management of unsuitable specimens. The article below summarises the work that has and will be done in these areas. The goal of this initiative is to ensure the EFLM WG-PRE produces work that meets the needs of the European laboratory medicine community. Progress made in the identified areas will be updated at the next preanalytical phase conference and show that we have produced guidance that has enhanced standardisation in the preanalytical phase and improved patient safety throughout Europe.

Complete blood count at the ED: preanalytic variables for hemoglobin and leukocytes

OBJECTIVE

The objective of this study is to determine the ways in which preanalytic factors related to physiologic status can affect the complete blood cell count (CBC) in patients referring to an emergency department (ED).

METHODS

Over a 1-year period, the results of hemoglobin (Hb) level and white blood cell (WBC) counts of the first CBC tests undertaken in consecutive patients (n = 11487) referring to the ED were compared with those obtained in the same patients at a second test undertaken within 24 hours of admission. A prospective evaluation of the same differences was made in another group (group 2) of 1025 consecutive ED patients, several clinical characteristics being taken into consideration.

RESULTS

Mean Hb concentrations were higher in the first (range, 8.0-15.9 g/dL) than in the second test results (median overestimation, 0.4-0.8 g/dL; P < .0001). At multivariate analysis of results in group 2 patients, fluid administration (>0.5 L) and the presence of edema played a significant role in the initial overestimation of Hb level (P = .001 and P = .045, respectively). The comparison between leukocyte counts (WBC) showed that values from the first were higher than those in the second test (median overestimation ranging from 0.42 to 3.63 × 10(9)/L cells, in the range counts from 4.0 to 30.0 × 10(9)/L). None of the clinical factors studied appeared to have affected this overestimation.

CONCLUSIONS

On interpreting CBC results in patients admitted to the ED, physicians must consider the effect of physiologic variables on Hb level (mainly hydration status) and WBC count (mental and physical stress).

The theory of reference values: an unfinished symphony

The history of the theory of reference values can be written as an unfinished symphony. The first movement, allegro con fuoco, played from 1960 to 1980: a mix of themes devoted to the study of biological variability (intra-, inter-individual, short- and long-term), preanalytical conditions, standardization of analytical methods, quality control, statistical tools for deriving reference limits, all of them complex variations developed on a central melody: the new concept of reference values that would replace the notion of normality whose definition was unclear. Additional contributions (multivariate reference values, use of reference limits from broad sets of patient data, drug interferences) conclude the movement on the variability of laboratory tests. The second movement, adagio, from 1980 to 2000, slowly develops and implements initial works. International and national recommendations were published by the IFCC-LM (International Federation of Clinical Chemistry and Laboratory Medicine) and scientific societies [French (SFBC), Spanish (SEQC), Scandinavian societies…]. Reference values are now topics of many textbooks and of several congresses, workshops, and round tables that are organized all over the world. Nowadays, reference values are part of current practice in all clinical laboratories, but not without difficulties, particularly for some laboratories to produce their own reference values and the unsuitability of the concept with respect to new technologies such as HPLC, GCMS, and PCR assays. Clinicians through consensus groups and practice guidelines have introduced their own tools, the decision limits, likelihood ratios and Reference Change Value (RCV), creating confusion among laboratorians and clinicians in substituting reference values and decision limits in laboratory reports. The rapid development of personalized medicine will eventually call for the use of individual reference values. The beginning of the second millennium is played allegro ma non-troppo from 2000 to 2012: the theory of reference values is back into fashion. The need to revise the concept is emerging. The manufacturers make a friendly pressure to facilitate the integration of Reference Intervals (RIs) in their technical documentation. Laboratorians are anxiously awaiting the solutions for what to do. The IFCC-LM creates Reference Intervals and Decision Limits Committee (C-RIDL) in 2005. Simultaneously, a joint working group IFCC-CLSI is created on the same topic. In 2008 the initial recommendations of IFCC-LM are revised and new guidelines are published by the Clinical and Laboratory Standards Institute (CLSI C28-A3). Fundamentals of the theory of reference values are not changed, but new avenues are explored: RIs transference, multicenter reference intervals, and a robust method for deriving RIs from small number of subjects. Concomitantly, other statistical methods are published such as bootstraps calculation and partitioning procedures. An alternative to recruiting healthy subjects proposes the use of biobanks conditional to the availability of controlled preanalytical conditions and of bioclinical data. The scope is also widening to include veterinary biology! During the early 2000s, several groups proposed the concept of 'Universal RIs' or 'Global RIs'. Still controversial, their applications await further investigations. The fourth movement, finale: beyond the methodological issues (statistical and analytical essentially), important questions remain unanswered. Do RIs intervene appropriately in medical decision-making? Are RIs really useful to the clinicians? Are evidence-based decision limits more appropriate? It should be appreciated that many laboratory tests represent a continuum that weakens the relevance of RIs. In addition, the boundaries between healthy and pathological states are shady areas influenced by many biological factors. In such a case the use of a single threshold is questionable. Wherever it will apply, individual reference values and reference change values have their place. A variation on an old theme! It is strange that in the period of personalized medicine (that is more stratified medicine), the concept of reference values which is based on stratification of homogeneous subgroups of healthy people could not be discussed and developed in conjunction with the stratification of sick patients. That is our message for the celebration of the 50th anniversary of Clinical Chemistry and Laboratory Medicine. Prospects are broad, enthusiasm is not lacking: much remains to be done, good luck for the new generations!

History of the preanalytical phase: a personal view

In the 70ies of the last century, ther term “preanalytical phase” was introduced in the literature. This term describes all actions and aspects of the “brain to brain circle” of the medical laboratory diagnostic procedure happening before the analytical phase. The author describes his personal experiences in the early seventies and the following history of increasing awareness of this phase as the main cause of “laboratory errors”. This includes the definitions of influence and interference factors as well as the first publications in book, internet, CD-Rom and recent App form over the past 40 years. In addition, a short summary of previous developments as prerequesits of laboratory diagnostic actions is described from the middle age matula for urine collection to the blood collection tubes, anticoagulants and centrifuges. The short review gives a personal view on the possible causes of missing awareness of preanalytical causes of error and future aspects of new techniques in regulation of requests to introduction of quality assurance programs for preanalytical factors.

Diurnal variation of hematology parameters in healthy young males: the Bispebjerg study of diurnal variations

PURPOSE

To evaluate the influence of time of day on the circulating concentrations of 21 hematology parameters.

MATERIALS AND METHODS

Venous blood samples were obtained under standardized circumstances from 24 healthy young men every third hour through 24 hours, nine time points in total. At each time point, the level of melatonin, iron, transferrin, transferrin saturation, ferritin, cobalamin, folate, red blood cells and white blood cells was measured. The data were analysed by rhythmometric statistical methods. The biological variations were calculated.

RESULTS

Significant oscillation of melatonin (p < 0.0001) with an amplitude (amp) of 19.84 pg/ml and a peak level at 03:34 h confirmed the normal 24-hour rhythms of the participants. Erythrocytes (p < 0.0001, amp = 0.15 × 10(12)/L), hemoglobin (p < 0.0001, amp = 0.29 mmol/L), hematocrit (p < 0.0001, amp = 0.01), iron (p < 0.0001, amp = 4.00μmol/L), transferrin (p = 0.03, amp = 1.41μmol/L), transferrin saturation (p < 0.0001, amp = 6.37%) and folate (p < 0.0001, amp = 1.55nmol/L) oscillated significantly, with gradually falling mean levels through the day to nadir around midnight. Leukocyte count (p < 0.0001, amp = 0.78 × 10(9)/L), neutrophils (p = 0.001, 0.31 × 10(9)/L), eosinophils (p < 0.0001, amp = 0.04 × 10(9)/L), monocytes (p = 0.0009, amp = 0.06 × 10(9)/L), lymphocytes (p < 0.0001, amp = 0.49 × 10(9)/L) oscillated significantly with gradually increasing mean levels through the day peaking at midnight. Iron, leukocytes and hemoglobin had the highest 24 hour oscillations in proportion to the reference intervals of the parameters for healthy young men.

CONCLUSIONS

Biochemical screenings are biased by diurnal variations, which must be considered when blood concentrations of these parameters are interpreted in the clinical setting.

The influence of diet upon liver function tests and serum lipids in healthy male volunteers resident in a Phase I unit

AIM

To investigate the effect of diet upon liver function tests and serum lipids within the restricted environment of a Phase I unit.

METHODS

An open randomized three-way crossover study was designed with subjects consuming three types of diet. The diets comprised, a balanced normal calorie diet, a high-carbohydrate high-calorie diet and a high-fat high-calorie diet. Each diet was consumed in a randomized sequence over 8 days with a recovery period of 14 days between periods. The blood concentrations of various laboratory parameters were measured at intervals throughout each dietary period and during the recovery periods.

RESULTS

Blood transaminase activity and triglyceride concentrations increased significantly whilst subjects consumed a high-carbohydrate high-calorie diet but not when fed either a high-fat high-calorie diet or a balanced normal calorie diet.

CONCLUSIONS

The rises in transaminases and triglycerides were caused by the carbohydrate content of the diet rather than its calorific value. Sucrose rather than starch was the carbohydrate which caused the rise in transaminases and triglycerides. The importance of controlling diet in Phase I studies is stressed.

Haematocrit: within-subject and seasonal variation

This review was undertaken, concerning within-subject biological variation and seasonal variation of haematocrit in normal healthy adults and athletes, to find the limits for natural, intra-individual variation in haematocrit values. The terminology and calculations followed well defined theories, from the field of laboratory medicine, about biological variation. Based on results from 12 studies of 638 normal healthy adults, and which used a sampling interval of 1 day to 1-2 months, the coefficient of within-subject biological variation of haematocrit is 3%. The normal within-subject biological variation (3%) and analytical variation (3%) may explain a relative change of approximately 12% (95% level) [e.g. a change from 0.42-0.47] between two successive haematocrit values, measured with a time interval between 1 day and 1-2 months, in a normal healthy adult. Partly due to haemodilution in warm weather, haematocrit often has a seasonal variation in normal healthy adults; based on results from 18 studies of 24 793 participants, the population mean is approximately 3% lower in summer than winter. Population mean values that are 7% lower in summer than winter have been found in some studies, although no seasonal effect may also be seen, especially in temperate climates. If haematocrit values are sampled at yearly peak and trough time points, with intervals of up to 6 months, a 15% relative change (95% level) can be seen in a normal healthy adult; e.g. a change from 0.42-0.48. Published values for haematocrit in athletes are scarce. It is known that the haematocrit value is influenced by training, especially in the first weeks before a new steady-state is reached. Theoretically, the biological variation in athletes could therefore be greater than in normal individuals. Based on two references addressing the biological variation of haematocrit in athletes, however, the above results are also valid for athletes. Further studies, both in the short term and throughout the seasons, are recommended about the natural variation of haematocrit in athletes.

The preanalytic phase. An important component of laboratory medicine

The preanalytic phase is an important component of total laboratory quality. A wide range of variables that affect the result for a patient from whom a specimen of blood or body fluid has been collected, including the procedure for collection, handling, and processing before analysis, constitute the preanalytic phase. Physiologic variables, such as lifestyle, age, and sex, and conditions such as pregnancy and menstruation, are some of the preanalytic phase factors. Endogenous variables such as drugs or circulating antibodies might interact with a specific method to yield spurious analytic results. The preanalytic phase variables affect a wide range of laboratory disciplines.

Preanalytical and analytical factors affecting laboratory results

The results of laboratory tests have a substantial role in the diagnostics of diseases. However, laboratory results do not always correspond with the patient's clinical status. They may be unexpected and surprising. On the other hand, an abnormal laboratory result may be accepted as such and interpreted as a sign of a disease. However, an abnormal result may result from several factors other than disease. Conventionally, these interfering factors have been divided into preanalytical and analytical factors and furthermore into factors acting in vivo and in vitro. The list of these factors is long and laborious to bear in mind. In this review we focus on the factors which, in practice, most often affect laboratory results in healthy individuals and which explain an unexpected result.

Preanalytical factors and standardized specimen collection: influence of psychological stress

In order to devise and evaluate standardized specimen collection procedures, we studied the influence of psychological stress on the results of commonly analysed blood components: creatine kinase, lactate dehydrogenase, total protein and albumin in serum and blood picture. In addition, serum cortisol was assayed. Two kinds of stress were used: the Stroop test, a colour conflict task, and the thrill caused by the first jump of new parachutists. More changes were observed after the parachutist test than after the Stroop test. There was a difference in the responses of males and females. Females were more sensitive, especially to the parachutist test. Most of the changes observed were interpreted as being caused by haemoconcentration, possibly related to muscular tension. Cortisol, commonly used to indicate the level of stress, did not react much and is therefore not a good index of psychological stress.

Experimental basis of standardized specimen collection: the effect of the site of venipuncture on the blood picture, the white blood cell differential count, and the serum albumin concentration

The effect of the specimen collection site on blood picture and WBC differential count was investigated in 13 and 25 volunteers, respectively. Lower values were found for the mature neutrophils and higher monocyte values in ear and finger blood compared to venous blood. There were no statistically significant differences in the WBC differential count values found in the ear and finger specimens. A higher S-Alb concentration was found in ear and finger specimens compared to venous blood. The average WBC concentration was higher in the ear and finger specimens than in the venous blood (7.66 x 10(9)/l, 7.11 x 10(9)/l and 6.88 x 10(9)/l, respectively). Also the platelet concentration exhibited a statistically significant difference, the mean concentrations being 273 x 10(9)/l, 260 x 10(9)/l and 231 x 10(9)/l in the vein, finger and ear specimens, respectively. The differences found are partly explained by peripheral ultrafiltration of intravascular fluid, leading to haemoconcentration, and partly by the different properties of different white blood cells. In conclusion, the specimens for blood picture and WBC differential count should always be obtained from the same site, especially in follow-up cases.

Experimental basis of standardized specimen collection: effect of posture on blood picture

22 subjectively healthy females were supine, sat in an armchair and stood while specimens of peripheral venous blood were collected after at least 15 min in each position without using a tourniquet. The albumin, haemoglobin, erythrocyte concentration and the haematocrit increased significantly when the subjects assumed a more erect position, probably as a result of increased hydrostatic pressure. The leucocyte count did not rise, and there was a statistically significant drop in the lymphocyte concentration when changing from supine to sitting. However, the leucocyte concentration rose significantly from supine to sitting or standing. When interpreting laboratory data, the difference in the behaviour of different cell species should be kept in mind. However, on the whole this study supports the stipulation contained in international recommendations that the posture of the subject should be standardized before collection of peripheral blood for haematological tests.

Experimental basis of standardized specimen collection: the effect of moderate ethanol consumption on some serum components (K, Na, ASAT, ALAT, CK, LD, total protein)

Venous blood was collected on two mornings from seven healthy volunteers using the standard Scandinavian procedure (fasting, sitting and no tourniquet) and serum Na, K, ASAT, ALAT, CK, LD and total protein were assayed. Then ethanol (0.75 g/kg body weight) was given on three consecutive evenings and the subsequent observed values 1, 3, 15, 38, 62 and 110 h post-ethanol were compared with the morning values. The mean component/total protein ratios dropped 14% for ASAT and 19% for ALAT 62 and 15 h post-ethanol, respectively. CK rose 17% at 3 h and dropped 17% at 62 h. However, the absolute values of ASAT, ALAT and CK did not change significantly. The only significant post-ethanol changes occurred in Na +2.14 mmol/l at 1 h (p less than 0.01), K -0.24 mmol/l at 3 h (p less than 0.05) and +0.26 mmol/l at 15 h (p less than 0.05), and LD +31 IU/l at 15 h (p less than 0.05) and +25 IU/l at 110 h (p less than 0.01). In one series, the total protein concentration dropped 4.57 g/l at 110 h post ethanol (p less than 0.001) but this drop was not reproducible in two additional series. It is concluded that moderate (social) ethanol consumption does not produce clinically significant effects on the components analysed. Also it may be misleading to express results as component/total protein ratios.

The effect of the order of filling tubes after venipuncture on serum potassium, total protein, and aspartate and alanine aminotransferases

The serum components mentioned were measured from the first and last tubes filled with blood following one venipuncture performed without use of a tourniquet on ordinary outpatients. The concentration of potassium was significantly higher in the first tube, whereas the concentration of the other components did not change. In a second series of experiments the first drops of blood (approximately 1 ml) emerging from the needle were collected separately. In the serum from this tube, the potassium concentration was significantly higher than in the serum from the second tube (approximately 10 ml), whereas the sodium concentration was the same. It is concluded that serum potassium should routinely be assayed from the second or a later tube of blood filled after one venipuncture. The S-ASAT, S-ALAT and S-total protein may be assayed from any tube.

Electrophysiologic study for ventricular arrhythmia: effect on total and myocardial-specific creatine kinase activity

To determine the potential for myocardial injury during electrophysiologic study for ventricular arrhythmia, total creatine kinase and creatine kinase B-subunit enzyme activity were serially measured after the procedure in 24 patients. During electrophysiologic study 14 of the 24 patients had sustained ventricular tachycardia or fibrillation, 4 patients had nonsustained ventricular tachycardia, and 6 patients had no ventricular arrhythmia induced. Cardioversion was necessary because of hemodynamic collapse in 9 of the 14 patients with sustained ventricular tachycardia or ventricular fibrillation. Coronary heart disease was present in 14 of the 24 patients, in 9 of the 14 with sustained ventricular tachycardia or ventricular fibrillation, and in 7 of the 9 patients requiring cardioversion. Total creatine kinase was modestly elevated (greater than twice baseline or greater than normal, or both) 24 hours after electrophysiologic study in 10 (42%) of the patients. Electrophysiologic study with or without the induction of ventricular tachycardia or ventricular fibrillation was not associated with increased creatine kinase B-subunit activity even in patients with coronary heart disease.

[Seasonal variation of blood components important for diagnosis (author's transl)]

In a comparative study, the differences between the values measured for 26 blood and serum components in both winter and summer were determined in 78 healthy subjects. Comparable conditions during the preparation of test persons, sampling, processing of specimens, and measurement were strictly observed. The term "season" is defined more precisely by meterological data. In the summer season, significantly higher values were found for leukocytes (9%), lactate dehydrogenase and MCHC (7% each), creatinine (7%, in women only), and MCH (1%) whereas significantly lower values were exhibited by aspartate aminotransferase (18%), alanine aminotransferase (14%), alkaline phosphatase (11%), glucose and packed cell volume (7% each), MCV (6%), total protein (2%), erythrocytes, albumin, sodium and chloride (1% each). These partly considerable alterations should be taken into account in the establishment of reference values and evaluation of laboratory findings (above all, when intraindividual comparison is involved). There were no significant alterations of the following parameters: hemoglobin, gamma-glutamyl transferase, urea, uric acid, creatinine (men only), bilirubin, cholesterol, total glycerol, potassium, calcium, and inorganic phosphate. In another series of experiments involving 32 test persons, the influence of different ambient temperatures during blood sampling on the above mentioned blood components was studied. Within the 18-30 degrees C range, no significant alterations were detected.