Urinary System Lecture PDF

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Summary

MLSC-3131U, Clinical Microbiology II Urine samples are the most common samples to receive in the lab. They are fairly easy to workup/report and one of the few samples that do quantitative analysis. Upper UTIs, pyelonephritis (kidney infection) and uteritis (uterus infection). Lower UTIs, cystitis (b...

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MLSC-3131U, Clinical Microbiology II -

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Urine samples are the most common samples to receive in the lab. They are fairly easy to workup/report and one of the few samples that do quantitative analysis. Upper UTIs, pyelonephritis (kidney infection) and uteritis (uterus infection). Lower UTIs, cystitis (bladder infection), urethritis (urethra infection) and prostatitis (prostate infection). UTIs are most commonly due to the proximity of the colon to the urethra, making transmission easier. Pyuria, WBCs in the urine. Urines will be centrifuged for sediment analysis for WBCs and bacteria. Nitrate testing will also be done on the urine (positive if bacteria are present) along with leukocyte esterase testing (positive if WBCs present). Urine will be yellow and cloudy if bacteria are present and infected urine will also produce a high pH/SG result and a positive nitrite/leukocyte/blood result. Bacteria would also be seen on a wet prep. Multiplex PCR, detects pathogens in urine such as N. gonorrhea, Chlamydia trachomatis, and Legionella.

Types of Urine -

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Voided Urines, non-sterile samples that include o Midstream Urine, patient is asked to cleanse the outer area, discharge some urine and then collect the urine expelled afterwards. o Neonatal Bagged Urine, a bag is placed around the babies urethra to catch urine whenever it is expelled. o Indwelling Catheter, has a balloon that inflates to block the bladder opening to prevent urine escaping. A drainage port is connected to a bag for urine collection. Normal flora commonly colonize these urines. o Ileal Conduit Urine, patient has a bag attached on the outside of the abdomen where urine by passes the urethra to be drained into the bag. In and Out Catheter, catheter is inserted temporarily for bladder drainage and then removed after collection. Aseptically Collected Urine, done surgically. o Nephrostomy, collected directly from the kidney. o Cystoscopy, collected directly from the bladder. o Suprapubic Bladder Aspirate, collected directly from the bladder via a syringe inserted through the suprapubic wall. Normal flora in urine includes Coagulase negative staph, Viridians streptococci, Lactobacilli, Diphtheroids, Corynebacterium and Propionibacterium spp. Anaerobic bacteria are not placed in ANO2 because they do not cause UTIs so we do not need to work them up.

MLSC-3131U, Clinical Microbiology II

Problems for Urine -

Contaminated and infected specimens can be hard to identify since the colon is so close and contamination is very common. Voided urines are rarely sterile because the urine is contaminated with normal flora during collection. Urine with counts less than 10^2 bacteria/mL of urine is considered contaminated through bad collection or poor refrigeration. Urines with colony counts between 10^2 and 10^4 are in a grey zone as to whether they are truly infected or contaminated. Urines with colony counts over 10^4 bacteria/mL are considered truly infected.

Laboratory Diagnosis of UTIs Specimen Collection -

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Urines are collected in a dry sterile container. Urine supports bacterial growth well so these samples are refrigerated immediately to stop growth. Urine is to be transported within 2 hours of collection. If this is not possible, it may be refrigerated for up to 24 hours during holding and transportation. Afterwards, it is rejected. Never freeze urine samples. Specimens can be rejected because they are easily recollected. They may be rejected if… o The sample is not refrigerated for greater than 2 hours after collection. o The sample has missing patient/collection information. o The sample is older than 24 hours. o The sample is a duplicate specimen obtained via the same collection method within 48 hours since the bladder does not change this fast. o The sample is in a leaky container. o The sample is transported inside of a foley catheter tip. STAT samples are rejected by calling the floor, giving the reason for rejection and documented who was contacted and who reported the rejected.

Specimen Set Up -

1 uL Loops, used for samples from midstream urines, indwelling catheters and in and out catheters. 10 uL Loops, used for samples from suprapubic aspiration or cystoscopies. Calibrated loop is immersed once vertically up and down into a gently mixed urine sample. No gram stain is performed on urine specimens. Media routinely inoculated with urine in the lab are CLED, Uriselect, BAP and MAC and incubated in O2 for 18-24. If the urine is cloudy, the urine is plated on CNA (isolates GPs

MLSC-3131U, Clinical Microbiology II

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and inhibits facultative anaerobic GNBs like proteus). Saborauds media is also used if fungi is suspected. Media is inoculated in a straight line with the loop. Next, a zig zag line is made as tightly as possible perpendicular to the initial line without crossing previous zig zags. CLED, non-inhibitory differential media containing lactose. Used for the cultivation and presumptive ID of urinary pathogens. Uses a bromothymol blue indicator which is yellow in the presence of lactose fermenters and blue in their absence. Deficient in electrolytes to prevent swarming of proteus. Uriselect, non-selective chromogenic differential media. Used for the direct ID of E. Coli, enterococcus and Proteus. BAP is always inoculated first because that is where our colony count is done. You can redip the loop and do the MAC plate afterwards. Both plates are incubated in O2 since the urinary organisms are not fastidious. Colony Counts, one bacteria on a plate is considered as one colony forming unit (CFU). The loop size is important in calculating the CFU since they differ in volume. For example, if 23 colonies grow on the BAP inoculated with a 1 uL loop, there would be 23 x 10^6 CFU/L (1 uL = 0.000001 L). No growth on the plate is reported as less than 1 x 10^6 CFU/L. Less than 10 x 10^6 CFU/L is reported as insignificant growth. 10 -100 x 10^6 CFU/L is reported as probable infection. Anything greater than 100 x 10^6 CFU/L is reported as infection. When working up a urine you must determine the sex of the patient, type of urine, total colony count and amount of different organisms growing through colonial morphology. Regardless of the colony count, Coagulase negative staph (except for S. saprophyticus in females), Neisseria, Lactobacilli, Diptheroids and Bacillus are reported as insignificant growth. Clinically significant urine pathogens include Enterobacterales, Staphylococcus saprophyticus (in females of childbearing age only), yeasts, beta-hemolytic strep, Enterococcus, NLFs and Staphylococcus aureus.

AST for UTIs -

These are always set up at the same time we set up our ID tests. Colonial morphology should give us a good idea of a presumptive ID. Attainable blood antibiotic levels often differ from attainable antibiotic urine levels since some antibiotics are excreted via the kidney. This gives certain antibiotics larger concentrations in the bladder (Nalidixic acid, Ampicillin, Cephalosporins, Ciprofloxacin and Nitrofurantoin)....