Summary
Uroflowmetry is one of the simplest and most frequently used non-invasive examinations of the lower urinary tract. The report shows the rate of urine flow during voiding, allowing for the assessment of maximum and average flow rates, voided volume, duration of voiding, various other parameters, and the shape of the flow curve itself.
Determining whether a measured urine flow rate is “normal” is not as straightforward as it might seem. A given flow rate can carry different clinical implications for a 25-year-old man compared to an 80-year-old man – especially if the former voids 100ml while the latter voids 400ml.
For this reason, nomograms have been developed for uroflowmetry to compare measured flowrates against reference values derived from a healthy population. Well-known examples include the Siroky, Liverpool, and Bristol nomograms, while the Miskolc nomogram and other more recent pediatric nomograms are particularly relevant for children.
A common limitation is that no single nomogram can, on its own, confirm or rule out a disorder or establish a diagnosis. For instance, a reduced flowrate could result from increased urethral resistance, weakened detrusor contractility, or a combination of both. This is also emphasized in the guidelines of the European Association of Urology (EAU).
1. Why do we need nomograms?
In uroflowmetry the most important parameter (second only to gender and age) is typically Qmax – the maximum urinary flowrate.
However, Qmax is influenced by numerous factors, primarily the voided volume, age, gender, detrusor function, and urethral resistance.
A nomogram is a graphical or mathematical model that compares a measured value against a reference population. Rather than relying on a single threshold (e.g., Qmax=15ml/s), it allows for an assessment of how expected a given flowrate is for a specific voided volume.
There are two primary methods of representation:
- Standard deviations (SD): the result indicates how many standard deviations the flowrate lies from the reference mean.
- Percentiles (or centiles): the result indicates the proportion of the reference population that exhibits an equal or lower flowrate.
For example, the 10th percentile means that approximately 10% of a comparable reference population had an equal or lower flowrate, while approximately 90% had a higher one. This does not, however, imply that the individual has a 90% probability of having an obstruction.
Clinically, it is therefore important to distinguish between a statistically low flowrate and a confirmed pathological disorder of bladder emptying.
2. Siroky nomogram (1979)
(American nomogram. Adult males. Standard deviations.)
In 1979, Siroky, Olsson, and Krane introduced one of the first widely used uroflowmetric nomograms. It was developed based on measurements from 80 asymptomatic men, and its primary purpose was to distinguish between expected and reduced flowrates.
How does it work?
Siroky nomogram shows flowrate as a function of bladder volume. The result is expressed in relation to the average for a healthy population and standard deviations.
Traditional interpretation:
- Around 0 SD: flow close to the expected average.
- Below -1 SD: flow is below average, but this does not necessarily indicate a disorder.
- Below -2 SD: significantly reduced flow relative to the reference population.
In a subsequent study from 1980, 98% of Qmax measurements in 53 patients with clinically evident obstruction fell below -2SD (standard deviation). Following successful surgery, the measurements shifted into the reference range. This result pertains to a specific clinical population and cannot be directly applied to general screening.
Advantages
- A long tradition of use and good recognition among urologists.
- Allows for the assessment of flow in relation to volume, rather than relying solely on a single Qmax threshold.
- Suitable for monitoring changes in flow before and after treatment.
- In addition to Qmax, a nomogram for average flow has also been developed.
Weaknesses
- It was developed based on a relatively small sample of men.
- Age is not directly included in the basic nomogram.
- It uses bladder volume as the volume parameter, rather than the volume of voided urine.
- It is not suitable as an originally validated reference model for women and children.
- It does not distinguish between obstruction and impaired detrusor contractility.
If the post-void residual (PVR) urine volume is large, using only the voided volume is not entirely consistent with the original model. Gammie in Abrams specifically drew attention to this.
Clinical assessment: The Siroky nomogram remains useful primarily in adult men, especially when monitoring the same patient; however, a result below -2SD should not be interpreted as definitive evidence of obstruction.
3. Liverpool nomogram (1989)
(British nomogram. Men and women. Percentiles.)
The Liverpool nomograms were developed by Haylen et al. in 1989. The study included 331 men and 249 women, representing a significant expansion compared to Siroky’s original study.
They established separate reference curves for Qmax and Qavg for both genders, covering voided volumes ranging from 15 to 600ml.
How does it work?
The Liverpool nomogram uses percentiles instead of standard deviations.
The nomograms for men and women are not the same. For men, the influence of age is also significant, as research has confirmed that flow rates decrease with age. In women, no statistically significant effect of age or the number of childbirths on the measured flow rates was found.
In a clinical comparative study from 1990, the authors proposed the following lower limits of normality for identifying patients at higher risk of voiding disorders:
| Population | Proposed lower limit |
|---|---|
| Men | 25. percentile |
| Women | 10. percentile |
The cut-off values were selected as part of a specific studyinvolving 504 men and 168 women who underwent urodynamic diagnostics. However, these are not universal diagnostic criteria.
Advantages
- Separate nomograms for men and women.
- Larger reference sample than in the Siroky study.
- Account for age in men.
- Display of Qmax and Qavg.
- Wide range of voided volumes.
- Percentiles are relatively easy to understand.
Weaknesses
- The reference male population was approximately 16-64 years old; therefore, application to older men constitutes an extrapolation. In practice, age adjustment for men is not always applied correctly.
- The percentile value alone does not indicate whether an obstruction is present.
- Results depend on the reference population and the chosen lower limit.
- The formulas involve logarithms and the calculation of roots.
Clinical assessment: Among the three nomograms considered, the Liverpool nomogram is particularly useful as a general reference model for adult men and women. For men, appropriate age adjustment must be applied. A major limitation is that it ends right around the age at which measurements typically begin.
4. Bristol nomogram (Kadow, 1985)
(British nomogram. Older men. Age-specific reference.)
The Bristol nomogram, also known as the Kadow nomogram, was developed in 1985 based on data from 123 asymptomatic men aged 50 to 80.
This is its key advantage: the reference population was specifically selected from among older men, in whom bladder-emptying difficulties are common.
Unlike the Siroky nomogram, it incorporates the voided volume. The mathematical model is logarithmic. Its equations were subsequently presented in a comparative analysis by Gammie and Abrams at the 2013 ICS meeting.
Advantages
- Developed specifically for men between the ages of 50 and 80.
- Takes into account that flowrate physiologically decreases with age.
- Suitable for interpreting measurements in older men, where using reference values from a younger population could lead to an increased number of seemingly pathological results.
- Its reference model focuses on a population in which uroflowmetry is frequently used due to lower urinary tract symptoms (LUTS).
Weaknesses
- Small reference sample.
- Not intended for women, children, or younger men.
- Less widely used and less commonly available in uroflowmetry software. The formula employs logarithms.
- Not a standalone diagnostic tool for obstruction.
- Lower expected flow values in older men may reduce sensitivity for certain clinically significant disorders, depending on the chosen threshold.
Clinical assessment: The Bristol nomogram is of interest primarily for the evaluation of uroflowmetry in older men. Its limited prevalence does not imply that it is unsuitable; however, the restricted reference population necessitates caution.
5. Direct comparison of three nomograms
| Property | Siroky | Liverpool | Bristol |
|---|---|---|---|
| Year | 1979 | 1989 | 1985 |
| Reference sample | 80 men | 331 men, 249 women | 123 men |
| Gender | male | both | male |
| Age | No direct correction | Correction in men (16-64 years) | 50-80 years |
| Volume | Bladder volume | Excretion volume | Excretion volume |
| Display | SD | Percentiles | Reference curves |
| Qavg nomogram | yes | yes | no |
| Main advantage | Classic comparability, simplicity | Broader applicability | Older men |
| Main limitation | Age and gender | Users are older than the reference sample | Narrow population |
The underlying data are derived from original research and a comparative analysis by Gammie and Abrams (ICS 2013).
The differences are not merely theoretical. Gammie and Abrams demonstrated that the same uroflowmetric result can fall into different reference ranges depending on the nomogram used and the chosen lower limit – particularly in older men.
Therefore, it is clinically inappropriate to treat different nomograms as entirely interchangeable.
6. Pediatric uroflowmetry nomograms
Nomograms designed for adults should not be applied uncritically to children.
Flowrates change during the course of development due to the growth of the bladder and urethra, as well as other anatomical and physiological factors. Relevant variables include age, sex, and bladder volume; some studies also consider body surface area.
Miskolc (Szabó in Fegyverneki, 1995)
The Miskolc nomogram is one of the best-known pediatric uroflowmetric nomograms.
The authors studied 200 healthy children, aged 3-18 years, and analyzed 433 voiding events. They developed reference curves for maximum and average flowrates.
Its advantages include a broad age range, a focus specifically on the pediatric population, and the ability to compare Qmax and Qavg against the voided volume.
Clinical assessment: The main limitations are the relatively small sample size, the fact that the data originate from only one country, and that interpretation may depend on whether the measurement is repeated.
Tzu Chi (Taiwan, 2014)
A Taiwanese research group developed pediatric nomograms based on 1128 children (583 boys and 545 girls) aged 4-12 years.
A unique feature of their approach is the comparison of the first measurement with the higher value obtained from two consecutive measurements. They demonstrated that Qmax is significantly dependent on age, gender, and voided volume.
The authors proposed approximate lower limits for Qmax – roughly 11.5ml/s for children aged <=6 years and 15ml/s for children aged >=7 years – based on approximately the 10th percentile of their two-measurement model. They also noted that external validation is required.
Clinical assessment: The Tzu Chi nomograms provide significant evidence that reference curves can vary between different pediatric models. For boys aged 8-12 years, the 5th percentile curve from the Miskolc model was lower than the corresponding curves from the Tzu Chi model.
Other pediatric nomograms
| Nomogram or Study | Population | Specific Feature |
|---|---|---|
| Jensen and colleagues, 1983 | 205 children, aged 3-13 | Measurements taken in a typical school or kindergarten setting |
| Gaum and colleagues, 1989 | 511 children | Influence of age and volume |
| Wese and colleagues, 1989 | 511 children | Body surface area as an important reference factor |
| Miskolc, 1995 | 200 children, aged 3-18 | Qmax and Qavg |
| Tzu Chi, 2014 | 1128 children, aged 4-12 | Comparison of single versus two measurements |
| Indian Pediatric Nomogram, 2022 | 440 children, aged 5-15 | Comparison by gender and age groups |
A 2022 Indian pediatric study confirmed that, among the children analyzed, the average Qmax was higher in girls (20.69 ml/s) than in boys (16.68 ml/s). This further underscores the importance of having separate pediatric reference values based on gender.
What is more important for children than the percentile itself? A urologist’s opinion.
In addition to Qmax, we always evaluate the shape of the flow curve, voided volume, residual urine, Qavg, and – most importantly – the clinical context.
A bell-shaped curve is the standard physiological pattern, whereas a staccato, interrupted, plateau-shaped, or an exceptionally high and short curve requires interpretation within the clinical context as is the case with all uroflowmetric findings.
A normal Qmax does not rule out dysfunctional voiding, just as an abnormal curve shape alone does not prove the presence of a neurological disorder.
Therefore, for pediatric uroflowmetry, it is appropriate to use a combination of a pediatric nomogram, repeated measurements, curve analysis, and assessment of post-void residual urine, supplemented (depending on the clinical indication) by EMG and urodynamic studies (UDS).
7. Do we need different nomograms for different ethnic and geographical populations?
The published nomograms were developed primarily based on local populations. Their validity for other populations, therefore, cannot be taken for granted.
India: PGIMER nomogram
In 2010, researchers from Chandigarh directly evaluated whether the Siroky and Liverpool nomograms were optimally applicable to Indian men.
They developed their own PGIMER nomogram, which employs a different mathematical relationship between flowrate and voided volume (a cubic relationship).
The comparison for Qmax showed (within the study population and using selected cut-off values):
| Nomogram | Sensitivity | Specificity |
|---|---|---|
| Siroky | 100% | 69,3% |
| Liverpool | 96,2% | 75,3% |
| PGIMER | 89,3% | 86,0% |
These results apply to the comparison within the study population and using selected cut-off values.
PGIMER thus achieved higher specificity but lower sensitivity. The authors concluded that nomograms developed based on European reference populations might not be optimal for the Indian population.
This is a significant finding; however, it does not prove that the cause of these differences is necessarily genetic or ethnic. The results may also be influenced by age distribution, physical characteristics, the measurement protocol, the position during urination, and the method used to select healthy subjects.
South Africa: differences among women
A 2020 study analyzed 336 women, 306 of whom were included in the reference-range development group.
A statistically significantly higher mean flow rate was observed in black women compared to white women (p=0.023). The researchers developed local reference curves but emphasized the need for further research into ethnic differences.
Statistical significance does not necessarily imply that the observed difference is sufficiently large or reliable to warrant the use of different clinical thresholds for an individual patient.
Chinese and other East Asian populations
The most directly verified example among the studies reviewed is the Tzu Chi pediatric nomogram from Taiwan.
Given the large Chinese population, one might expect the existence of Chinese nomograms; however, while preparing this article, author of this article did not find any that are widely accepted in academic databases. If you happen to come across any, please let me know via the contact page above.
In my view, rather than focusing on the country of origin, it is more important to verify the age, gender, volume, and measurement protocol for which a specific model has been validated.
Native American population and Inuit
In North American literature, there is further research on age- and volume-adjusted flow rates—for example, the work of Drach et al., as well as a 1994 population-based analysis of flow rates in relation to age and volume. The study by Oesterling et al. is another example.
However, I have not found a properly verified, specifically validated uroflowmetric nomogram for Inuit or North American Indigenous populations. If you happen to come across one, please let me know via the contact page above.
Do ethnic differences among men have any practical significance?
At present, there is no evidence to support the claim that a different nomogram should be selected for each man based solely on his ethnicity.
Studies from India suggest that a local nomogram may improve certain statistical classification properties. However, this does not, in itself, translate to better clinical decision-making or improved treatment outcomes…
Consequently, in routine urological practice, factors such as age, voided volume, measurement quality, curve shape, post-void residual (PVR) urine, and clinical symptoms are generally more directly useful than ethnicity. This represents a practical judgment based on existing evidence, rather than proof that population-based differences do not exist.
8. Which other nomograms are also worth mentioning?
In addition to the three most well-known models, there are also models specifically designed to account for age.
The Balslev-Jørgensen nomogram (1986) is based on a study of 93 older, asymptomatic men. The authors observed a decrease in the median Qmax from 18.5ml/s at age 50 to 6.5ml/s at age 80. This effectively illustrates the importance of age when interpreting flowrates, althoughsome older, seemingly asymptomatic men may already have an obstruction or impaired contractility.
Drach’s age-adjusted models further explored the relationship between Qmax, age, and voided volume.
9. What do modern guidelines tell us about nomograms?
The EAU guidelines for men with LUTS recommend uroflowmetry during the initial assessment and prior to pharmacological or invasive treatment. They note that the measurement is best performed with an adequate bladder volume, typically exceeding 150ml, and should be repeated if the result is unrepresentative.
Regarding Qmax, they also point out an important diagnostic limitation:
| Qmax in men | Clinical significance |
|---|---|
| <10ml/s | Higher probability of obstruction, though hypocontractility is also possible |
| 10-15ml/s | Intermediate range; clinical interpretation required |
| >15ml/s | Obstruction cannot be ruled out |
These are not universal limits of normality, but rather a guide for assessing the likelihood of obstruction!
The 2017 ICI-RS report on the diagnostic utility of uroflowmetry also notes that the sensitivity and specificity of nomograms are limited, and that better standardization and the combination of non-invasive indicators are required.
10. What would an ideal modern nomogram be like?
This reflects the personal opinion of the author of this article:
Classic nomograms originated at a time when digital data acquisition, automated processing, and repeated home-based measurements were significantly less accessible.
As early as 2013, Gammie and Abrams proposed a model that would integrate Qmax, voided volume, PVR, and age.
Modern systems facilitate the easier determination of correlations. Rather than evaluating Qmax alone, it would be sensible to consider multiple interrelated data points:
- Qmax and Qavg, and their ratio.
- Voided volume, age, and sex.
- Post-void residual urine (PVR), when measured.
- Curve shape and the presence of artifacts.
- Changes between consecutive measurements.
The use of an individual reference curve would also be of interest: rather than comparing a patient solely against the general population, one could monitor whether their flowrate (at comparable volumes) changes over time. This further underscores the value of obtaining early measurements while an individual is still in a ‘healthy’ state.
This approach would be particularly useful for home-based uroflowmetry. However, any such new algorithm would first require clinical validation to determine whether it actually enhances diagnostic utility.
Conclusion
Siroky, Liverpool, and Bristol are three established approaches to the interpretation of uroflowmetry. They all seek to answer a similar question: is the measured flowrate as expected when compared to a reference population?
There are significant differences among them regarding the size and composition of the reference groups, the voided volumes used, the consideration of age, and the method of statistical presentation.
The Liverpool nomogram is particularly useful because it provides separate reference values for both genders and includes age adjustments for men. The Siroky nomogram remains an important historical and clinical reference model, while the Bristol nomogram is of particular interest for older men.
In children, the use of pediatric nomograms is essential, as adult reference values cannot be directly applied. The Miskolc and Tzu Chi nomograms are notable examples that also illustrate the impact of population selection and measurement methodology.
Although some studies suggest differences between geographical and ethnic populations, there is currently insufficient evidence to justify the use of separate, ethnicity-based nomograms for the routine assessment of all adult patients.
The most important takeaway is that a nomogram assesses the relative magnitude of the flowrate, not the underlying cause of any reduction. Therefore, the final interpretation must always take into account the clinical presentation, the quality of the measurement, and where necessary the results of additional investigations.
All articles on https://www.ipeewell.com/ were written by urologist Rok Rodič. iPeeWell is the manufacturer of iPeeWell uroflowmeters for home and professional use.
Literature
Classic nomograms
1. Siroky MB, Olsson CA, Krane RJ. (1979). The flow rate nomogram: I. Development. Journal of Urology. PubMed
2. Siroky MB, Olsson CA, Krane RJ. (1980). The flow rate nomogram: II. Clinical correlation. Journal of Urology. PubMed
3. Haylen BT et al. (1989). Maximum and average urine flow rates in normal male and female populations: the Liverpool nomograms. British Journal of Urology. PubMed
4. Haylen BT et al. (1990). Urine flow rates in male and female urodynamic patients compared with the Liverpool nomograms. British Journal of Urology. PubMed
5. Gammie A, Abrams P. (2013). The characteristics and improvement of urine flow rate nomograms. ICS Abstract 631. Vključuje podatke in enačbe Kadowjevega oziroma Bristolskega nomograma. ICS, celotno besedilo
6. Balslev Jørgensen J et al. (1986). Uroflowmetry in asymptomatic elderly males. British Journal of Urology. Izvirni članek
Pediatric nomograms
7. Szabó L, Fegyverneki S. (1995). Maximum and average urine flow rates in normal children: the Miskolc nomograms. PubMed
8. Yang SS et al. (2014). The Tzu Chi nomograms for maximum urinary flow rate in children: comparison with Miskolc nomogram. PubMed
9. Gaum LD et al. (1989). Age related flow rate nomograms in a normal pediatric population. PubMed
10. Wese FX et al. (1989). Body surface related flow rate nomograms in a normal pediatric population. PubMed
11. Uroflowmetric analysis and derivation of nomograms for normal paediatric Indian population between 5 to 15 years of age. (2022). PubMed
Population comparisons and modern guidelines
12. Agarwal MM et al. (2010). Are urine flow-volume nomograms developed on Caucasian men optimally applicable for Indian men? Indian Journal of Urology. Celoten članek, odprt dostop
13. Age, gender, and voided volume dependency of peak urinary flow rate and uroflowmetry nomogram in the Indian population. Celoten članek
14. Abdool Z et al. (2020). A study to establish normal reference values of urine flow parameters in healthy South African females. Članek
15. Gammie A et al. (2018). The fundamentals of uroflowmetry practice, based on International Continence Society good urodynamic practices recommendations. Članek
16. EAU. (2026). Guidelines on the Management of Non-neurogenic Male LUTS, Diagnostic Evaluation. Aktualne smernice