Factors affecting serum creatine phosphokinase levels in normal adult females

Distribution of serum creatine kinase activity in young healthy persons

The normal distribution of serum creatine kinase (CK) was determined in 428 men (mean age = 21.5) and 540 women (mean age = 20.2). The bootstrap method was employed to obtain statistical parameters of CK reference range and correlations with physical activity habits, BMI, cigarette smoking and alcohol consumption. CK distribution was non-Gaussian and skewed toward the higher values; 18.9% of the men and 4.6% of the women had values above the upper reference limits defined for the commercial assay kit. The median 97.5 percentile value was 532 u/l for men and 248 u/l for women (95% confidence interval of 384-738 u/l and 184-340 u/l, respectively). A significant correlation was found only between CK and alcohol consumption in men. Myoglobin level in a representative group of subjects correlated well with CK activity for both genders. Our findings define the range of CK values in a healthy, young, heterogeneous population. We suggest that only CK levels above the determined 97.5 percentile should warrant further clinical investigation.

Race-gender differences in serum creatine kinase activity: a study among South Africans

Higher levels of total serum creatine kinase activity have been reported in black compared with white North Americans of the same sex. In a study among South Africans, we found such an interracial difference was notable only for males. The difference was heightened by physical activity. This study affirms the importance of sampling the indigenous population when developing a reference range for total creatine kinase activity.

The creatine kinase reference interval. An assessment of intra- and inter-individual variation

Serum creatine kinase (CK) values in reference populations generally vary by greater than one order of magnitude. This large range of variation overlaps the range of values found in female carriers of Duchenne muscular dystrophy and limits the clinical usefulness of serum CK testing. In order to examine whether the source of this variation is intrinsic variability of individual CK values, or whether the variation is due to day-to-day variation in each individual's CK activities, we tested 15 female medical students at weekly and 22 female medical students on at least 3 occasions. Each venesection followed a 3-day exercise free interval, according to a standard protocol, designed to minimise the effects of exercise. Each individual tended to have consistent CK activities. The range of variation in the same individuals on different occasions was small (the mean coefficient of variation, CV was 19%). There was a much greater range of serum CK activities between individuals (CV 47%). Even when sporting activities were excluded slightly higher values were found after minor exercise was recorded in the three days prior to venesection. The conclusion that individuals have consistent serum CK activities was supported by the results from a larger population tested under standardised resting conditions on three different occasions which yielded similar frequency distributions on each occasion.

Variation of serum myoglobin levels in normal individuals. With reference to the use of myoglobin measurements for the detection of women carrying genes for the X-linked muscular dystrophies

The extent of variation in the serum myoglobin (Mb) levels of normal healthy females were investigated so that the value of Mb measurements for carrier detection could be properly assessed. Factors considered were sex, age, menstrual status, pregnancy, diurnal variation and daily activity. In each instance, Mb levels were compared with those for serum creatine kinase (CK). A significant difference (P less than 0.001) was found between the Mb levels of men and women but no relationship could be found between several measurements of body build and the Mb or CK levels of either sex. An apparent correlation of Mb concentrations with age was found in control groups of both sexes up to 85 years of age, but this was not significant below 60 years of age. No differences in Mb levels were found among premenarchal, menstruating, postmenopausal or hysterectomised women and neither smoking nor the use of oral contraceptives seemed to affect Mb levels. Serum CK levels were very much higher in premenarchal (P less than 0.001) and postmenarchal (P less than 0.05) teenagers than in adult controls. No difference was found between the mean Mb levels of non-pregnant and pregnant (6-40 weeks) women. The mean value for CK activity was significantly lower than normal in the pregnant women (P less than 0.001). A marked circadian rhythm of serum MB levels was found with samples taken at 5 p.m. being approximately 20% lower than those taken at 9 a.m. This unexpected decrease during the day persisted with 48 hours of bedrest suggesting that this rhythm is inherent and unrelated to muscular activity.

Creatine kinase

Creatine kinase is present in significant concentrations in skeletal muscle and cardiac muscle and to a lesser extent in gastrointestinal tract and brain tissue. The enzyme has been purified from a variety of tissues and an examination of its kinetic and physical properties reveal that the enzyme consists of two subunits and can exist as three isoenzymes containing essential cysteine residues. These properties are important in understanding its stability, the assay conditions, and the techniques used to identify the different isoenzymes. The relationship between the properties and the determination of the enzyme in biological fluids will be a main thrust of the review. Creatine kinase activity in serum rises rapidly in conditions such as acute myocardial infarction and trauma to skeletal muscle. However, the interpretation of such increases is dependent upon a sound knowledge of the factors which influence both the total and isoenzyme activities. The nature of these factors will be discussed in detail.

Serum myoglobin in muscular dystrophy and carrier detection

Serum myoglobin was measured by radioimmunoassay in 143 patients with various muscle diseases including 55 boys with Duchenne dystrophy, 56 carriers of the Duchenne dystrophy gene, 8 carriers of the Becker dystrophy gene, 60 first-degree relatives of patients with sporadic (non-genetically transmitted) muscle diseases and 85 normal controls. A significant difference (P less than 0.001) was found between the serum myoglobin levels in normal control men (x = 31.7 range 10-70 microgram/l) and those in women (x = 17.2 range 4-27 microgram/l) but no difference was found between the controls and relatives of patients with muscle disease. Up to the age of 60 years, no correlation was found between age and serum myoglobin levels in controls. However, levels in boys with Duchenne dystrophy were found to increase slightly up to the age of 10 years and to decrease thereafter. No correlation was found between serum myoglobin and creatine kinase activity in these boys but in Duchenne carriers correlation was close (P less than 0.001). Eighteen of 23 definite and 13 of 33 possible carriers of Duchenne dystrophy had myoglobin concentrations above the equivalent normal range. Of those carriers with elevated myoglobin levels, 7 definite and 4 possible carriers had normal serum creatine kinase activity. This was equivalent to an improvement in "detection" of 31% and 12% in these groups of carriers. Of the 8 Becker dystrophy carriers, 6 had elevated myoglobin but all had normal creatine kinase levels. It appears that measurement of serum myoglobin as well as creatine kinase activity may be of great benefit to carrier detection programmers, but the need to establish accurately the extent of normal variation in women is emphasized.

Interpretation of serum creatine kinase in suspected myocardial infarction

Serum creatine kinase (CK) was measured in blood donors, patients admitted to hospital with suspected myocardial infarction, and healthy hospital personnel to investigate the normal range, the daily variation in healthy people, and the effect of intramuscular injections of pentazocine or diamorphine.There was considerable daily variation in the healthy controls, apparently related to exercise. In defining both the normal range and the significance of day-to-day increases in the serum CK account should be taken of this factor. An upper limit of normal of 210 IU/1. Should apply to previously ambulant patients and of 165 IU/1. to patients previously at rest. An increase greater than 85% in successive daily values is uncommon in health.Intramuscular injections of both pentazocine and diamorphine caused a significant rise in the serum CK in six out of 25 patients. The highest rise observed was from 64 IU/1. to 395 IU/1. Caution is therefore urged in the diagnosis of myocardial infarction from the serum CK values when these intramuscular injections have been given.