Examining the microscopic appearance of urine sediment

Microscopic examination of the urine sediment is an essential part of the urinalysis, as it allows for confirmation and clarification of urine dipstick findings. It also allows for the identification of elements not evaluated by the urine dipstick, including red blood cells, white blood cells, epithelial cells, crystals, and casts.

Master the ins and outs of kidney function tests. Order and interpret these tests with full confidence knowing that you’ve conquered this critical skill!

Taking a shotgun approach to kidney function testing can be tempting if nephrology is not your forte. By the end of this course, however, you’ll be comfortable ordering and interpreting all common kidney function tests. After this course, you’ll understand the clinical implications of abnormalities seen on these tests and will be able to form a practical plan of action.

Microscopic examination of the urine sediment is an essential part of the urine analysis, as it enables confirmation and clarification of urine dipstick findings. It also allows identification of structures that are not evaluated by the urine dipstick. These include red blood cells, white blood cells, and epithelial cells from all levels of the urinary tract, as well as crystals and casts.

Hematuria may be grossly visible or microscopic. Microscopic hematuria is commonly defined as the presence of two or more red blood cells per high-powered field in a spun urine sediment. Isomorphic red blood cells have an appearance similar to erythrocytes in the circulation, which are small anucleated and biconcave disks, and can be seen with any cause of hematuria.

By contrast, dysmorphic red blood cells have an altered morphology and their presence is suggestive of glomerular disease. The first step in evaluating unexplained hematuria is to distinguish between glomerular and non-glomerular causes which may involve the kidney or bladder. Glomerular causes of hematuria are mostly due to glomerular nephritis, which is inflammation and damage of the glomeruli.

Glomerular nephritis is further subdivided into proliferative and non-proliferative glomerulonephritis. Proliferative glomerulonephritis may present as acute renal failure. Or, proliferative glomerulonephritis can present with nephrotic syndrome, which includes hematuria hypotension, oliguria, red blood cell casts and mild to moderate proteinuria.

Non-proliferative glomerulonephritis may present with proteinuria or hematuria, or with nephrotic syndrome. Severe proteinuria, edema, hypoalbuminemia, hyperlipidemia, and hypertension. Non-glomerular causes of hematuria may come from the upper urinary tract or the lower urinary tract.

Examples of hematuria from the upper urinary tract include renal stones, pyelonephritis, and tumors of the kidney. Examples of hematuria from the lower urinary tract include urinary tract infection, enlargement of the prostate, tumors and surgical instrumentation. White blood cells in the urine include neutrophils and eosinophils.

Urinary neutrophils are commonly associated with bacteriuria. However, if the corresponding urine culture is negative, known as sterile pyuria, than interstitial nephritis, which is inflammation of the interstitium of the kidney, renal tuberculosis, and nephrolithiasis should be considered. The presence of eosinophiluria has classically been considered a marker of acute interstitial nephritis.

Epithelial cells may appear in the urine after being shed from anywhere within the genital urinary tract. Thus, epithelial cells are often a normal finding in the urine. In some conditions, such as those associated with tubular damage, you may see increased number of epithelial cells in the urine.

In proliferative glomerulonephritis, there is an increase in the number of cells in the glomerulus, including an increase in the number of endothelial cells in the capillaries, epithelial cells from Bowman's capsule, and mesangial cells in the interstitium of the glomerulus. However, proliferative glomerulonephritis patients often have the same number of epithelial cells in their urine as normal patients. So the number of epithelial cells in the urine can be used for diagnosis in this case. We'll examine casts and crystals in the next Medmastery lesson.