Chronic Bacterial Prostatitis Workup

EPS, postmassage urine culture, or semen culture must be obtained for a precise diagnosis of chronic bacterial prostatitis (CBP).^[10] The spectrum of organisms grown in culture in CBP is essentially the same as in acute bacterial prostatitis. Most infections are caused by a single pathogen, but a polymicrobial infection is not unusual. Obligate anaerobic bacteria rarely cause prostatic infection.

Localization cultures do not need to demonstrate more than 100,000 colony-forming units (CFU) per milliliter to establish the diagnosis (see the image below). Instead, the presence of a greater than 10-fold bacterial growth in the EPS or the third midstream bladder specimen (VB₃) compared with the first voided bladder specimen (VB₁) and the second midstream bladder specimen (VB₂) is important.

The various prostatitis syndromes have been classified based on EPS and culture findings. This classification system is important for therapy because the various categories are treated differently. The presence of 10 or more WBCs/HPF in the EPS is considered clinically significant inflammation.

Acute bacterial prostatitis is an uncommon, but potentially life-threatening, type of prostatitis. It is characterized by high fever, chills, malaise, and myalgias, in addition to voiding symptoms. EPS should not be obtained in acute bacterial prostatitis because of the risk of potentiating bacteremia.

If testing in a patient with chronic bacteriuria does not reveal CBP, referral to a urologist is advisable. Chronic bacteriuria should prompt an investigation for underlying causes, such as urinary stasis, infection, stones, abscess, and/or obstruction. In this situation, evaluation of the upper urinary tract with a radiologic imaging study such as an intravenous pyelography (IVP), renal ultrasonography, or computed tomography (CT) scanning is often performed. In addition, chronic bacteriuria in the absence of CBP may prompt evaluation of the bladder with cystoscopy.

Histologic findings

Chronic inflammation is common after biopsy specimens have been obtained to help evaluate for prostate cancer. Findings usually include large, focal lymphocytic infiltrates amid the normal prostatic stroma; however, biopsy rarely, if ever, is used to diagnose prostatitis. If an asymptomatic patient is found to have inflammation in the prostatic tissue, this is categorized as category IV prostatitis, ie, asymptomatic inflammatory prostatitis. (See the image below.)

Commonly, chronic prostatitis is diagnosed after microscopic examination of the EPS and a positive culture finding after a prostatic massage. If a patient presents with symptoms of an acute urinary tract infection and/or the patient is febrile, an EPS should not be obtained, because the patient likely has acute prostatitis. In this situation, a vigorous prostatic massage may result in urinary sepsis.

The generally accepted level of WBCs in an EPS for a diagnosis of chronic prostatitis (category II in the NIH classification) is more than 10 WBCs/HPF (40X objective) or an observation of clumping WBCs with the presence of oval fat bodies and a positive EPS culture finding.

Category III prostatitis is divided into IIIa and IIIb, based on whether greater or fewer than 10 WBCs are seen on microscopic examination of the EPS, respectively. However, the management approaches for these 2 categories do not differ.

Finding WBCs in an EPS is not diagnostic of chronic bacterial prostatitis (CBP), because this finding is commonly associated with nonbacterial prostatitis, urethritis, prostatic stones, or recent ejaculation.

EPS findings based on the type of prostatitis are as follows:

• Chronic bacterial prostatitis (CBP) - The EPS usually contains greater than 10 WBCs/HPF and should be obtained; unlike patients with acute bacterial prostatitis, these patients are not acutely ill
• Acute bacterial prostatitis - The EPS should not be obtained, because of the risk of potentiating bacteremia, but if the EPS has been inadvertently obtained, sheets of WBCs are present; the voided urine reveals significant bacterial growth due to accompanying cystitis
• Nonbacterial prostatitis - The prostate is significantly inflamed, as revealed by more than 10 WBCs/HPF, but routine bacterial culture does not demonstrate growth of organisms; Cultures for fungi, Chlamydia, Ureaplasma, and Mycoplasma rarely demonstrate growth
• Prostatodynia - No inflammation in the EPS or bacterial growth in culture is present; Pelvic-perineal pain appropriately describes the symptoms of this condition

Performing this procedure helps to confirm the diagnosis of CBP. The classic 4-glass Meares-Stamey test for localization of the infection to the prostate is cumbersome and impractical. A more sensitive, simpler, and more practical test to help confirm the diagnosis of CBP is preprostatic and postprostatic massage urine culture.^[11] The ejaculate can also be cultured; this may indicate a prostatic infectious source.

Carefully observe the culture for a colony count that is 10 times higher in the postprostatic massage culture than in the preprostatic massage culture, which confirms CBP. This is the widely accepted standard.

Perform the prostatic massage during the rectal examination by kneading the prostate from front to back and from lateral to medial until a milky fluid is obtained from the urethra. This may require as long as a minute of fairly vigorous massage; therefore, inform the patient of the intended plan and goal. Sometimes, milking the urethra hastens the appearance of the fluid. Then, touch the fluid to a microscopic slide for examination. The pH of prostatic fluid rises when infection is present, from 6.5 to higher than 8.0.

Routine prostate-specific antigen (PSA) testing during a prostatitis episode is not recommended. Most patients with clinically proven bacterial prostatitis have an elevated PSA value independent of any cancer-related elevation. No prostatitis-adjusted tables are available to indicate which PSA values are inappropriate in this patient population.

In patients with bacterial prostatitis who have an elevated PSA value, a reevaluation of the PSA value 6-8 weeks after appropriate treatment is recommended to ensure the value is decreasing to normal levels. It is also appropriate to review the patient’s recent PSA values as a point of comparison. If values remain elevated after appropriate therapy, prostate biopsy is recommended to rule out concomitant pathology.

Historically, the criterion standard for diagnosis has been the 3-cup bacterial localization study. This test represents the classic method for the diagnosis of bacterial prostatitis. The technique was described initially by Meares and Stamey in 1968.^[12] Clinically, the 3-cup test has proven time-consuming and cumbersome; thus, its use as a diagnostic tool is declining. Obtaining urine cultures prior to and following prostatic massage have arisen as clinically useful alternatives to the 3-cup test.

Magri et al conducted a retrospective study of semen cultures and found them to be a useful adjunctive diagnostic tool.^[13] However, further studies are needed to confirm these findings and to determine if semen culture alone may represent a reasonable diagnostic alternative.

The 3-cup test is performed best when the bladder urine is sterile. If the bladder urine is not sterile, an oral antibiotic such as nitrofurantoin may be prescribed to sterilize the bladder urine. Nitrofurantoin achieves excellent bladder concentrations but does not produce significant intraprostatic levels. The method for performing a 3-cup test is described below.

Technique

VB₁ represents any bacterial growth within the urethra. The patient is asked to retract the foreskin, if present, and cleanse the meatus. The VB₁ is the first 5-10 mL of voided urine and should be collected in a sterile cup.

After the VB₁ collection, the patient urinates another 100-150 mL of urine. The next 10-15 mL is collected in a sterile cup and represents VB₂, the bladder component of any bacterial growth.

The EPS represents the prostate contribution. The EPS is obtained by massaging and compressing the prostate gland until a drop of fluid is obtained. The EPS is examined under high power in a microscope. More than 10 WBCs/HPF is abnormal and consistent with prostatic inflammation. In addition to WBCs, the EPS may contain oval bodies, which are fat-containing macrophages; these also indicate inflammation.

The VB₃ represents a mixture of prostatic fluid and bladder urine. The VB₃ is the first 5-10 mL of urine obtained after the prostate massage for the EPS. Similarly, this VB₃ is sent for culture.

This study is not helpful unless an abscess exists. Abscesses are extremely rare, but if they are present, patients may also have a high fever and appear quite ill. CT scanning may also be helpful in this situation if transrectal ultrasonography is not available. Magnetic resonance imaging (MRI) may also be used but is not as readily available in most acute situations.

Transrectal ultrasonography findings may also help to identify prostatic stones. In certain patients with frequent recurrences, these stones may be a contributing factor in chronic bacterial prostatitis (CBP).

However, transrectal ultrasonography cannot be used to actually diagnose CBP. Although hypoechoic lesions calcifications within prostate may suggest the infection and inflammation associated with CBP, these findings are highly nonspecific.

This is the most definitive, but least practical, modality used to diagnose bacterial prostatitis. It is also potentially dangerous for the patient.

Viewing the specimen under microscopy can help to identify a focal infiltration of inflammatory cells into the prostatic stroma. The specimen also serves as a source from which to culture organisms. However, in the face of an active infection such as acute prostatitis, performing a biopsy could precipitate sepsis. Therefore, prostate biopsy is not recommended as a diagnostic modality.

On the other hand, category IV prostatitis is diagnosed using prostate biopsy. Category IV prostatitis is asymptomatic but may be responsible for elevations in PSA levels, resulting in the need for a diagnostic biopsy to help exclude prostate cancer.

Retrograde urethrography

Retrograde urethrography is performed to help confirm the presence of a urethral stricture. It is performed by injecting contrast into the urethral meatus and obtaining pelvic radiography. If a stricture is present, narrowing of urethral caliber is observed.

Uroflowmetry

Uroflowmetry is a simple, urodynamic test to help evaluate the rate of urine flow over time. It is used in patients with prostatitis to help evaluate for obstruction secondary to a urethral stricture or prostatic enlargement. Results are obtained in graphic form. Normal study results show a rapid rise to a peak and then a gradual drop-off back to baseline. A urethral stricture is indicated by a rapid rise to a low point, a plateau for the remainder of the study, and then a drop-off at the termination of the study.

In prostatic enlargement, a wide variety of patterns is present, but the peak flow is usually less than 15 mL/s, and a stop-start pattern may also be present. To help delineate abnormalities and to differentiate a stricture from prostatic enlargement, cystoscopy should be performed.

Postvoid residual testing

Postvoid residual testing measures the volume of urine left in the bladder immediately after voiding. This volume can be measured by catheterizing the bladder or by using a bladder scanner. Although the results are nonspecific, they can give clues to the presence of lower tract dysfunction, which may require surgical intervention to relieve prostatic obstruction or urethral stricture.