Amniotic Fluid Ferning Pattern. Ferning is the arborization pattern found when a drop of amniotic fluid is allowed to air dry on a microscope slide and helps distinguish rupture of the amniotic sac in pregnancy from normal vaginal secretions. (Photo contributor: Robert Buckley, MD.)
To evaluate for the presence of cells, casts, and crystals.
Freshly collected urine specimen, centrifuge, graduated centrifuge tubes, glass microscope slide, and coverslip.
Pour 10 mL of freshly collected urine into a graduated centrifuge tube.
Centrifuge at ×400 to ×450 gravity for 5 minutes.
Decant 9 mL of supernatant, leaving 1 mL in the tube.
Resuspend the centrifuged pellet in the remaining 1 mL of urine by stirring with a pipet.
Place one drop of resuspended urine on a glass microscope slide.
Overlay with a coverslip.
Examine initially using scanning ×10 power, emphasizing the periphery of the coverslip, since urinary elements tend to gather at the edges.
Switch to ×40 power to focus on specific urinary elements such as cells, casts, and crystals. Use ×100 power as needed for specific identification.
Calcium Oxalate Crystals. Calcium oxalate crystals come in two shapes. The classically described octahedral, or envelope-shaped, crystals are made of calcium oxalate dihydrate. Calcium oxalate monohydrate crystals are needle-shaped. They are seen in acid or neutral urine. They may be found in the urine of patients with ethylene glycol ingestion. In addition, the urine of patients with ethylene glycol ingestion may also fluoresce under a Wood lamp. (Reproduced with permission from Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 4th ed. Philadelphia, PA: F.A. Davis Company; 2001, p. 97.)
Uric Acid Crystals. Uric acid crystals often have a yellow hue and a variety of sizes and shapes. They are found in acidic urine. (Reproduced with permission from Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 5th ed. Philadelphia, PA: F.A. Davis Company; 2008, p. 114.)
White Blood Cell Casts. Usually two to three cells in width, white blood cell casts are indicative of upper urinary tract infection such as pyelonephritis. (Photo contributor: American Society for Clinical Pathology.)
Red Blood Cell Casts. Red blood cells casts range from 3 to 10 cells in width and are seen in glomerulonephritis. (Photo contributor: American Society for Clinical Pathology.)