THE EFFECT OF CLIMATE UPON THE VOLUMES OF BLOOD AND OF TISSUE FLUID IN MAN

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.

Nutritional status of middle-aged and elderly females in Kentucky in two seasons: Part 2. Hematological parameters

There is some indication that change of seasons, from summer to winter, alters certain hematological parameters that could be indicative of hemodilution and hemoconcentration. To investigate this further, we studied adult females (n = 130) aged between 51 and 86 years during summer and winter to evaluate any seasonal variations in selected hematological and related parameters. Data included a 7-day food intake, anthropometry, and hematological analysis of fasting blood. Erythrocyte and leukocyte counts, hematocrit (HCT), and hemoglobin (Hb) increased significantly in the winter compared to summer (p less than 0.01), but intakes of folacin, vitamin B12, and iron did not change. No effects of age or race were observed on these changes. Significantly elevated leukocyte counts (p less than 0.002), HCT (p less than 0.03), and Hb (p less than 0.007) were observed among smokers; however, smoking had no effect on the seasonal changes in hematological values. The increase in HCT was greater for persons using diuretics than those who were not on diuretics (p less than 0.05). The seasonal changes in erythrocyte counts (p less than 0.01), HCT (p less than 0.01), and Hb (p less than 0.05) were significantly correlated to the changes in plasma protein concentration among the subjects, suggesting hemoconcentration in winter and hemodilution in summer to some extent. The present study suggests that seasonal variation may occur in hematological parameters and that these factors should be taken into consideration when evaluating survey data.

Blood volume expansion among blacks: an hypothesis

Black persons are believed to have developed in a tropical environment and an expanded blood volume would have facilitated adaptation to such an environment. Throughout most of the first half of the life cycle blacks have slower heart rates than whites, and several lines of evidence suggest that heart rate is inversely related to blood volume. Review of blood volume studies in normotensive whites and normotensive blacks does not permit any conclusion concerning the blood volume hypothesis. Among patients with hypertension results of blood volume studies are inconsistent, but indirect evidence suggests that black patients with hypertension have greater plasma volume expansion than white patients with hypertension.

[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.