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How should you work up a patient who presents with a complaint of urinary frequency? What questions are useful to ask when taking the patient's history? Are there specific signs that you should look for in the initial physical examination? Are there tests or other assessments that you should order? What is the differential diagnosis for this symptom? Also, once you've made a diagnosis, what can you do to help this patient?

The purpose of this article -- the first in a series on urologic presenting symptoms -- is to provide clinicians with a basic step-by-step guide for assessing and treating patients who present with urinary frequency. Although the list of possible etiologies given below and management algorithm in Figure 1 may seem daunting, we hope to show that the primary care provider may successfully identify the underlying cause of this symptom and provide effective treatment in many cases; in addition, we describe the indications for referral:

Polyuria (increased fluid intake):
Primary polydipsia:
Diabetes mellitus

Diabetes insipidus (DI)

Medications: diuretics, belladonna, atropine, and caffeine

Psychological.
Diminished functional bladder capacity (FBC):
Nonneurogenic:

Bladder infection/inflammation/interstitial cystitis

Bladder outlet obstruction

Men -- prostatic and bladder neck, strictures

Women -- pelvic organ prolapse, post surgical

Incomplete bladder emptying

Pregnancy

Bladder cancer

Bladder stones.
Neurogenic bladder:

Stroke

Multiple sclerosis

Diabetes mellitus

Parkinson's disease

Hydrocephalus

Brain tumor

Traumatic brain injury

Spinal cord injury/tumor

Myelodysplasia

Transverse myelitis.
Psychosocial:

Habit/social

Defensive voiding (incontinence, pelvic pain syndromes)

Medical advice (kidney stones, diet, and medication).

Definition of Urinary Frequency

First of all, just what do we mean by the term "urinary frequency"? Simply put, it is defined as urinating more often than normal, but how often is normal? Most people void about 6-8 times in a 24-hour period. Large surveys and bladder diary studies in the United States and Europe found that the upper limit of normal is 8 voids per 24 hours.[1,2] Does this mean that a patient who urinates more than 8 times a day is in need of treatment? Not necessarily. Decisions concerning management depend on the cause of the frequency and the degree of bother that it causes the patient. Nevertheless, because we have postulated urinary frequency as the presenting symptom, we can assume that it causes at least some degree of bother to the patient. However, before we can think about treatment, we'll need to determine the cause of the frequency.
Diagnostic Evaluation

As the first step in the process of unraveling the cause of a patient's frequency, the clinician will need to get a more exact picture of the patient's voiding habits. It is a good idea to administer a focused questionnaire before taking a medical history because responses to the questions can be a useful guide in your history taking. There are a number of validated questionnaires designed to assess lower urinary tract symptoms. The questionnaire provided is the one that we use; we believe that it contains almost all of the questions that need to be asked about urinary symptoms. Of course, in a busy primary care practice, such a focused questionnaire may be impractical. At a minimum, the patient should be asked to estimate how often he/she voids and the approximate volume voided (eg, half a cup) per void. The patient should also be asked to specify the reason for voiding: normal urge, pain, fear of incontinence, fear of pain, or social convenience (eg, before a movie). How long has the patient been experiencing frequency -- days, weeks, months, or years? Are there any other storage or voiding symptoms that suggest urinary tract infection, overactive bladder, or difficulty voiding?

The need for physical examination is dictated by the nature of the symptoms. For patients with mild symptoms, no exam is necessary unless there is a suspicion of urinary retention (voiding frequently in small amounts in the absence of symptoms of infection, difficulty voiding, or symptoms of overflow incontinence). Urinalysis should be done, and if there is pyuria or hematuria, culture should be obtained and the patient treated with culture-specific antibiotics. Gross hematuria and microhematuria, of course, require referral for cystoscopy and upper tract imaging (computed tomographic scan [CT] with intravenous contrast or magnetic resonance imaging [MRI]). Before the end of the first visit, instruct the patient to keep a bladder diary

The bladder diary helps quantify the patient's qualitative symptoms. It provides information on the maximum functional capacity, patterns of urination (eg, what times of day the patient typically voids), the actual number of episodes of urination (patients often overestimate the frequency of urination), and provides clues as to the cause of nocturia (eg, whether it is caused by nocturnal polyuria or decreased nighttime bladder capacity). The diary can also help clarify the patient's history (polyuria or normal amounts of urine production) and direct further questions (eg, concerning the amount of liquids consumed during particular periods in the day). In patients with polyuria, a full physical examination is mandatory and can elucidate causes, such as heart failure, endocrine abnormalities, lower extremity edema, or a genitourinary cancer.

The Basics of Urinary Frequency

How frequently a person urinates depends on 3 basic factors: the volume of the 24-hour urinary output, the capacity of the bladder, and -- for lack of a better word -- psychosocial considerations.

Volume of Urinary Output

The volume of urinary output, of course, depends almost entirely on intake of fluid and food. (Remember that most foods are 60% to 90% water.) Under ordinary circumstances urine excretion is about 70% of oral fluid intake,[3] but urine output can be greatly diminished by abnormal fluid losses due to excessive sweating (from exercise, exposure to high temperature, tachypnea, etc). Oral fluid and food intake is extremely variable and dependent on not only metabolic and pathologic conditions, but social and psychological factors as well. Of course, diuretic use and liquids that contain diuretics, such as coffee and other caffeinated beverages, may greatly increase urine output.

Bladder Capacity

Bladder capacity is the maximum volume of urine that a patient can comfortably hold. Determining a patient's bladder capacity, however, is not a simple matter of measuring the volume of urine that he or she voids. Various factors besides quantity of urine can trigger the sensations that we perceive as an urge to void. For example, in some people spicy foods or caffeine (independent of the diuretic effect) cause a strong urge to void at low bladder volumes. Psychosocial and environmental factors, such as being distracted by some specific activities (exercise, intense concentration) can increase bladder capacity. Of course, urinary tract infection, involuntary bladder contractions, and urethral obstruction have just the opposite effect. Most people involuntarily retain a certain amount of urine in the bladder after voiding. The amount of the leftover or postvoid residual (PVR) urine varies greatly from person to person and generally increases with age. Because measurement of the volume of a patient's PVR is not usually carried out by nonspecialists, determination of the actual capacity of a patient's bladder is not often done in a primary care setting. However, another measurement is useful. The maximum voided volume (MVV) or FBC is the volume of the patient's single most copious void during a given time period. Although median MVV has been calculated (from a series of 300 diaries in "normal" patients) to be 330 mL (mean, 204 mL), the range of recorded volumes was large (90-1020 mL), with the 95th percentile of MVV at 679 mL.[1]

Assessment of Bladder Capacity

A patient's bladder capacity can be assessed by 2 very different techniques: the frequency/volume chart (bladder diary) and cystometry.

The frequency/volume chart is a diary in which the patient records the time and volume of each urination over a specified period of time, usually 1, 3, or 7 days. For most clinical purposes, a 1-day diary suffices.[4] The patient is given a preprinted diary form to fill out and is asked to void each time into a measuring cup. The measuring cup may be something as ubiquitous as a disposable coffee cup (of course, the volume that the cup holds must be known), or it may be a graduated cylinder. The FBC is equivalent to the largest voided volume reported in the diary.

If a patient has an FBC of 200 mL and voids 1800 mL in 24 hours, he/she is obligated to void at least 9 times. Of course, most patients do not wait until the bladder is completely full, and therefore void more often than would be predicted solely on the basis of the FBC.

Cystometric bladder capacity (CBC) is defined as the volume at which the patient can no longer delay micturition during cystometry. CBC depends on a number of technical factors, including the rate of bladder infusion, temperature of the infusant, and type of infusant. Further, CBC may be at great variance from the FBC.[5,6] For routine clinical purposes, the FBC and CBC are sufficient; CBC is mostly of interest to urologists.

Psychosocial Factors

Psychosocial factors also play a major role in the frequency of urination, especially in New York City, where we have our practice. Someone apparently told the inhabitants of this city that it is very healthy to drink a lot of water. New York City water, which comes from the Adirondack Mountains, is said to be the best in the country, but for some reason New Yorkers seem to prefer bottled water from other places. Many of our patients often carry plastic water bottles with them and imbibe a lot of water, sometimes voiding in excess of 4 L a day. These patients also void very frequently! Other patients drink a lot because they are on diets and were told that it's good to drink a lot when you are on a diet. Some drink to prevent kidney stones and others are said to have psychogenic polydipsia. We usually advise patients with urinary frequency who drink excessive amounts to cut back and drink when prompted by thirst unless there is a specific medical reason to do otherwise.

Interpreting the Bladder Diary

When the patient returns with a completed diary, the clinician can begin to narrow the diagnosis. First, count the number of voids in the 24-hour period to confirm that the patient is indeed experiencing urinary frequency (> 8 voids per 24 hours). If so, then observe the total quantity of urine voided over the 24-hour period. The clinician needs to determine whether the patient is urinating a lot because he or she has an abnormally large volume of urine to void or because his or her bladder is holding less than a normal amount. Those patients who void more than 2.8 L in a day are said to have polyuria. Those patients with an FBC of < 150 mL are said to have diminished FBC.[1,2] Many patients, though, do not, strictly speaking, fit into this classification because they have a normal FBC, yet void frequently in small amounts for reasons that defy easy explanation. See Figure 3A for a diary typical of a patient with polyuria, and Figure 3B for one indicative of diminished bladder capacity.

Polyuria

For patients with polyuria, empirical treatment is initiated by having the patient consciously reduce his/her oral fluid intake. To facilitate this, we ask the patient to simply drink according to thirst, but filling the glass only halfway. If the patient is still thirsty, he or she is instructed to drink another half glass and so on. While on this regimen, the patient is asked to complete another bladder diary. For the vast majority of patients, this "treatment" is effective and no further evaluation is necessary. Patients with functional causes of polyuria have no problem complying with this, but those with poorly controlled diabetes mellitus, DI, and disorders of thirst (dipsogenic polyuria) are unable to do so. For these patients a more thorough evaluation is necessary.

Uncontrolled diabetes mellitus, which leads to hyperglycemia and osmotic diuresis, is easily checked by fasting blood sugar. DI is further divided into central and nephrogenic DI. Central DI is caused by deficient synthesis of antidiuretic hormone (ADH) secondary to loss of neurosecretory neurons in the hypothalamus or posterior hypophysis. Nephrogenic DI is due to an inability of the kidneys to respond to ADH. DI and polydipsia can be distinguished from one another by the water deprivation test.[7] The patient fasts overnight and the first morning urine specimen is checked for osmolality. We believe that specific gravity on dipstick is inaccurate and urine osmolality is the preferred test. Osmolality greater than 800 mOsm/kg H2O indicates that there is normal ADH secretion and normal renal response to ADH. Thus, a normal water deprivation test means that polyuria is due to primary polydipsia. Primary polydipsia is either dipsogenic or psychogenic. Dipsogenic polydipsia is associated with a history of central neurologic abnormality, such as prior brain trauma, radiation, or surgery. There is no known medical treatment for dipsogenic polydipsia. Psychogenic polydipsia is a long-term behavioral or psychiatric disorder treated with behavioral modification to reduce fluid intake; unfortunately, many patients areresistant to such treatment.

Diminished Bladder Capacity

Diminished bladder capacity is not a straightforward diagnosis because many patients void at much lower volumes than their FBC. Of course, if all of the voids were at MVV, the diagnosis of reduced bladder capacity would be easy; in fact, most patients void at greatly varying voided volumes. Sometimes they void in small amounts for psychosocial reasons (for example, before a long car ride) and other times they void at their MVV. When evaluating the diary, it is pivotal to ask patients why they voided when the voided volumes were low. If it was because of urge, discomfort, or pain, one should look for infectious and inflammatory causes and be cognizant that it could be idiopathic overactive bladder, or there could be a subtle neurologic etiology or even bladder cancer.

Women urinate more often during pregnancy because their bladders don't hold as much, probably because of the weight of the uterus pushing on the bladder. Other conditions, such as radiation treatments to the lower abdomen, multiple operations on the bladder, and interstitial cystitis, also greatly reduce the capacity of the bladder.

Involuntary bladder contractions (detrusor overactivity [DO]) are a common cause of urinary frequency. There are many causes of DO that can be divided into 2 main groups -- neurogenic and nonneurogenic DO -- depending on whether there is an underlying neurologic disorder, such as multiple sclerosis. Nonneurogenic conditions associated with DO included benign prostatic hyperplasia and prostatic obstruction in men, and stress incontinence and genital prolapse in women. Much of the time, when these underlying conditions are successfully treated the DO subsides as well.


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