It can even influence human behavior, such as aggression and competitiveness. As you grow older, the level of testosterone in your body gradually decreases. This can lead to a variety of changes such as reduced sex drive. Testosterone levels reach their peak around age 18 or 19 before declining throughout the remainder of adulthood. Testosterone is necessary for normal fetal development during pregnancy.
It controls the development of the male reproductive system. Testosterone levels in the womb may also affect how your right and left brain function, according to one study that looked at 60 children. Testosterone levels have to fall within a very narrow margin in order for the fetal brain to be healthy. High levels of fetal testosterone may be linked to autism. In boys, the first physical signs of testosterone, or androgens, in the body are apparent during puberty. In premenopausal women, testosterone is made mainly in the ovaries.
Levels will decline after menopause , which usually begins between ages 45 and A testosterone test measures the level of the hormone in your blood. Some people are born with conditions that cause low testosterone levels. You may have a low testosterone level if you have an illness that causes damage to your testicles or ovaries, which make the hormone.
Levels may drop as you grow older. However, the U. If you feel that you may have low testosterone levels, you should see your doctor and get a test. Testosterone is the main male hormone, but women also need it for healthy body functioning. Testosterone is found in women at much lower levels than in men. This may make her levels of male hormones, also known as androgens, somewhat higher. Diseases such as polycystic ovarian syndrome PCOS can also raise testosterone levels.
In some cases a second test will come back slightly higher and the patient will be turned away or denied treatment. We also know that the NHS will drag out the process and it can take up to a year of blood testing and if one test comes back slightly higher than 7 then your only option will be private treatment.
The NHS will only look at total testosterone and not free testosterone or Shbg. The NICE guidelines are adhered to as strict rules rather then general guidance all in the name of cost cutting austerity.
When it comes to safely being treated for testosterone deficiency the NHS may be the provider of last resort. Free testosterone is the amount or portion of testosterone not bound by blood proteins which include both albumin and ShBG or sex hormone binding globulin.
Both these proteins can bind your testosterone with varying affinities. Albumin is more weakly bound to testosterone and this testosterone albumin affinity is called bioavailable testosterone because the albumin can more easily disassociate than Shbg can from testosterone. The SHBG binds tightly to testosterone and traditionally has been considered unusable with no biological function other than to leave you deficient. Some will argue that to lower Shbg is not ideal because of this although the traditional view and the view of many practitioners is to take the free testosterone level seriously as men with normal total testosterone but high Shbg and therefore low calculated levels of free testosterone report symptoms of low testosterone similar to men with low total levels.
A study published in addresses the importance of using the free or calculated free testosterone as a tool to diagnose low testosterone. In fact it demonstrated that men with low free testosterone suffered some of the worst symptoms compared to men with low total testosterone. Most assays or blood tests that directly measure free testosterone may be flawed or vary from lab to lab so the accuracy and precision can be called into question.
A more reliable tool and one used in most peer review studies is the calculated free testosterone level. Calculated free uses the results from albumin, total testosterone and SHGB to calculate free testosterone. You can calculate your free testosterone using our free testosterone calculator here. Balance my Hormones offers complete testosterone tests and always includes total, Shbg, albumin, and calculated free for the same price or less than some blood testing companies charge for a total only test.
If you would like your testosterone tests professionally checked by industry experts please use our contact form at the bottom of the page. In the UK calculated free testosterone levels are given in nanomoles per litre.
A normal range is anything above 0. Different countries and labs use different ranges and units of measure. To convert your testosterone results click here. Book Free Consultation. Looking only at narrowly defined reference ranges without considering symptoms, calculated free testosterone, and Shbg is folly.
Other tools may include comparing your blood levels from the past to the present may reveal that you are deficient when stacked up against by our past self. But if you had higher levels when you were younger and drop from 35 to 20 you may have all the symptoms of low T as you had been previously accustomed not more generous levels despite being in the standard or normal range.
Chances are you will have normal total levels but with age your SHGB will choke off your free testosterone leaving you low and symptomatic. Balance My Hormones can help get your testosterone levels tested. Testosterone can be measured in the blood, urine or saliva. The problem with salivary tests is that any cut in the mouth may taint the saliva sample with blood leading to inflated levels or inaccurate readings. The community standard of care in the UK and thought most of the world is a serum blood test for determination of testosterone deficiency syndrome.
The blood test can be produced through a venus sample normally taken from the vein in arm, and occasionally from a capillary sample taken from a fingerprick test. The accuracy of the fingerprick test varies and the extraction method can be difficult for some to collect enough blood for proper analysis. Nonetheless a fingerprick or capillary test can be used reliably at home with little risk or discomfort and posted back to the lab.
This makes it more convenient for collecting early morning samples. If you are concerned you might have low or high levels of testosterone, fill out our form below and we will get you tested as soon as possible and put you on the path to optimal hormone balance. Contact one of our medical doctors today to get your blood analysed for low testosterone or speak to one of our consultants about your health concerns.
The below links are scientific references, resources to perform further analysis and reading along with studies that have been conducted:. This article has been researched and written based on scientific evidence and fact sheets that have then been crossed checked by our team of doctors and subject matter experts.
References, sources and studies used alongside our own in-house research have been cited below, most of which contain external clickable links to reviewed scientific paper that contain date stamped evidence. We strive to provide you with the latest evidence based, researched articles that are unbiased, honest and provide you with accurate insights, statistics and helpful information on the discussed topic to ensure you gain a better understanding of the subject. We value your feedback on our articles, if you have a well-researched paper you would like to share with us please contact us.
If you know your total testosterone reading from a previous blood test input the results to the left above to see if your testosterone levels are normal. You may have low testosterone depending on the symptoms you have, please contact us to find out how we can help. You must be over 38, have had your ovaries removed or have suffered with premature menopause to warrant further hormone tests. Please contact us to discuss your hormones, we need your total testosterone levels to validate your hormone deficiency.
You can order a blood test here. You appear to have higher than normal testosterone levels, please contact us for further investigation. The diagnosis is based on clinical and biochemical findings and has been shown to be associated with impaired sexual function, impaired cognitive function [7] , [8] , depression [9] , abdominal obesity, low bone and muscle mass [10] , diabetes, and prediabetic states including insulin resistance, impaired glucose tolerance and the metabolic syndrome that may lead to an increase in risk of cardiovascular disease [11] — [13].
Overall, cardiovascular mortality is increased in late-onset hypogonadism [14] , [15]. Testosterone replacement in young hypogonadal men results in significant improvement of libido and sexual function and is of clear benefit [16] , but it remains to be established in older men that general health and other manifestations of the metabolic syndrome are improved [17] — [19].
As the diagnosis of hypogonadism includes identification of serum testosterone levels below the normal range for healthy males, there is an underlying assumption that normal ranges of testosterone for the healthy population are known for all ages.
However, to our knowledge, no such reference model exists in the literature, and hence the identification of individuals as hypogonadal does not have a widely applicable biochemical basis. In this study we derive and validate a normative model of TT across the lifespan. Using an established methodology [22] — [24] , studies containing TT measurements of healthy human males at a known age were identified by performing Medline and Embase searches, using the search terms Humans, Testosterone, Males and Reference values.
The reference lists of selected studies were checked, and cited references were retrieved to identify further relevant studies. Manuscripts were included for analysis if they reported TT levels for healthy normal males with no known testicular or endocrinological disorders.
Data from subjects with an identified chronic illness or on testosterone replacement therapy were excluded from the dataset, as were data from fetal blood and cord blood. These studies provided the basis for a dataset for TT that approximates the healthy human population from childhood to old age. Twenty-seven studies were identified that met the inclusion criteria; eleven studies were excluded because only descriptive statistics for study data were reported [25] — [35].
For the remaining sixteen studies, data were extracted from scatterplots using Web Plot Digitizer v2. Longitudinal data were recorded as cross-sectional values. Data were also censored at age 3 years: extracted values below this age failed to match the descriptive statistics published with the chart, and therefore could not be used to model accurately the height or age of the expected peak in TT in early infancy.
All data in this study were extracted from existing publications in the scientific and medical literature. Data relating to individual human subjects was not included and therefore specific ethical approval was not required. Zero TT values at conception were added to the combined dataset, in order to force models through the only known level at any age; these values were not taken into account when calculating model errors and fit.
Since variability increases with testosterone level, the data were log-adjusted after adding one to each value so that zero testosterone on a chart represents zero testosterone level. Each model defines a generic type of curve and has parameters which, when instantiated gives a specific curve of that type. For each model we calculated values for the parameters that maximise the r 2 coefficient. The Levenberg-Marquardt non-linear curve-fitting algorithm was used throughout, with convergence to 9 significant figures after a maximum of 4, iterations, for models having up to 21 parameters.
For each candidate model, the mean square error and r 2 were calculated after removing the artificial zero values at conception. In addition LOESS regression [45] was used to investigate the possibility that the best predictive model may be an ensemble of locally linear or quadratic models, rather than a single model covering all age ranges.
The best performing family of models were rational polynomials. For each subset S, the other four subsets were used to train rational polynomials having 3—11 parameters, with subset S being held back as test data.
The mean square error of the test data was calculated and compared to the mean square error of training data for the same model. In other words, the estimated prediction error of a model when generalized to unseen data was compared to the training error of the model. A model was considered validated if. Model coefficients a — f are given in Table 2 , and relationship to the data given in Figure 1.
Figure 3 is an exemplar of the 5-fold validation process in which a model is chosen that neither overfits nor underfits the underlying dataset. The residuals are the variations in log-adjusted observed values from the log-adjusted age-related mean value predicted by the model. High test and training errors represent underfit i. The optimal number of model parameters is seven in this instance, and in the analysis of the four other cross validation sets.
Our log-unadjusted normative model Figure 4 provides average TT values for the entire age range, together with normative ranges in terms of standard deviations away from age-related mean levels. The same model is given in terms of centiles in Figure 5. Residual plots for each decade of age are supplied as supporting information Figure S1a—h , as are the remaining cross-validation plots Figure S2 , and the TableCurve inputs and output for the validated model Table S1.
Mean and normative ranges for serum TT in healthy males are given for ages from 3 to 88 years in Table 3. Normative ranges for the model of total testosterone from ages 3—88 years. However, the variance in normative ranges increases for these ages, with 1 st to 99 th centile ranges of 5.
We show that TT peaks [mean 2. However we do show that there is an increased variation in TT levels with advancing age after age 40 years. Using data-driven modelling and analysis, we have derived a normative model of total testosterone throughout the lifespan. We have shown that in the average healthy male testosterone is low in pre-puberty, rises from age 11 and peaks at age 19 at Thereafter TT falls slightly to age 40 years to Previous studies of TT have reported contradictory results.
Whilst some studies show a decline in serum TT with age throughout life, other studies report no change in testosterone levels after approximately age 35 years. In particular, from the studies used as a basis for our dataset, Travison et al.
Halmenschlager et al. Our analysis of the combined data from 13 studies shows that TT levels do not decline after age 40 years in the average case. We now compare our results with those reported in studies that were not used to form our dataset. For each study we supply the number of subjects involved, n, to aid comparison with the studies used as a basis for our dataset.
Rohmann et al. However they report geometric means as opposed to arithmetic means and do not report the sample size for each calculation, so a detailed comparison of their results to ours is not possible. Muller et al. Frost et al. Rhoden et al. Taken together, these studies provide partial qualitative external validation for our model, but do not completely resolve the issue of contradictory single-centre study outcomes.
Our model is derived from data from multiple sources of the measurement of TT in over 10, healthy males aged between 3 and years. This is both a strength and weakness of the study. The strength is that modelling power is increased by the provision of large numbers of datapoints for a wide range of ages: it has been previously shown that models that include both prepubertal, pubertal and adult ages can be used to derive important insights for a restricted age range [47].
The weakness is the approximate heterogeneity of the values obtained from diverse sources, especially as assay conversion factors were used that have known high correlation but are nevertheless inexact. This includes studies that involve convenience samples e. Further limitations of our approach are that insufficient data were found to model accurately neonatal ages, and that we had to exclude potentially useful studies that used in-house assays which lack standardisation and harmonisation, and for which no conversion formula has been published [48].
We can therefore not rule out the possibility that a small number of subjects were on medication that increased their TT levels. Our results suggest that the reported increase in the proportion of hypogonadal men with increasing age can be attributed to the increase in variance of testosterone levels with increasing age, as opposed to an age-related decline in testosterone levels for the population as a whole.
These assertions are incorrect since it is not possible to have more than 2. However, if the definition of hypogonadism is based on a TT level lower than a fixed value, then the prevalence of hypogonadism will indeed increase due to increased variance with advancing age. As shown above, the majority of cross-sectional studies either report no decline in the average case, or a moderate annual decline in testosterone levels. Again, the disparity between the common explanation given and the data in the literature is that a greater proportion of individuals have lower levels of testosterone with increasing age.
There is disagreement on the indications for the use of hormonal therapy in men with apparently age-related low testosterone concentrations [51] , [52]. Our analysis of the combined data from several studies agrees to a certain extent with both sides of the controversy. We find no evidence that TT declines in the average case after the age of 40 years for ageing males. We do find that the prevalence of higher and lower testosterone levels increases with age, and hence that there is a larger number of men potentially at risk of androgen-related disorders.
Our study shows that the increasing proportion of men commonly regarded as having abnormally low or high levels of TT can be accounted for by the increase in variance in testosterone levels with age.
Factors that have been identfied as determinants of lower testosterone include obesity in many studies, as well as the development of other co-morbidities [53] — [55]. Obesity was not an exclusion criteria for our data acquistion, and our age-related reference ranges can be used for quantitative evaluation of the relationship between high body-mass index and low testosterone. There is increasing concern over testosterone supplementation in men, both generally and more particulary in those with comorbidities [20] , [21].
Whether all or subgroups of older hypogonadal men might benefit from replacement requires critical assessment, for which a robustly-established normal range provides an important basis.
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