Urinary tract infections: Pathology review

Two people came to the Nephrology ward.

The first one is 25 year old Carmen who recently returned from her honeymoon and now complains of suprapubic pain, dysuria and urinary frequency.

The other one is 35 year old Pamela who has had dysuria, fever, nausea and flank pain for the past 2 days.

On physical exam, she has costovertebral angle tenderness.

CBC and urinalysis were done for both people.

They showed that Carmen had a normal white blood cell count, but on the dipstick test, leukocyte esterase and nitrites were both positive.

For Pamela, the white blood count was high, the dipstick test showed positive leukocyte esterase and nitrites, and on microscopy, there’s white blood cell casts in the urine.

Both Pamela and Carmen have urinary tract infections, or UTIs.

This includes the lower portion of the tract like the bladder and urethra, and the upper portion of the tract like the kidneys and ureters.

UTIs are almost always caused by an ascending infection, where bacteria moves from the rectal area to the urethra and then migrate up the urethra and into the bladder.

Normally, bacteria would be washed away with urination, but in some cases, like with E. Coli, that doesn’t happen.

Instead, E. Coli uses little thread-like extensions called fimbriae to bind the uroepithelial cells and colonize the bladder mucosa, causing cystitis.

From the bladder, the infection can go up the ureter and into the kidney, where they attract neutrophils into the renal interstitium, causing pyelonephritis.

As neutrophils die off, they make their way through the urinary tract and appear in the urine.

The neutrophils and the surrounding inflammatory protein debris is even “casted” into the shape of the tubule, creating white blood cell casts and hyaline casts.