[Haematology] Microscopic Examination of Urinary Sediment - MISCELLANEOUS STRUCTURES

MISCELLANEOUS STRUCTURES, Microscopic Examination of Urinary Sediment, Graff's Textbook of Urinalysis and Body Fluids, [Haematology] Microscopic Examination of Urinary Sediment - MISCELLANEOUS STRUCTURES

Read more: 

1. [Haematology] Microscopic Examination of Urinary Sediment - Cells
2. [Haematology] Microscopic Examination of Urinary Sediment - Crystals
3. [Haematology] Microscopic Examination of Urinary Sediment - CASTS

MISCELLANEOUS STRUCTURES

Other structures which may be present in the urine include bacteria, yeast, cylindroids, spermatozoa, mucus and fat. Chemical analysis does not detect most of these types of sediment. Microscopic evaluation of urinary sediment is important if these structures are to be detected.

BACTERIA

The urine is normally free of bacteria while in the kidney and bladder, but contamination may occur from bacteria present in the urethra or vagina, or from other external sources.

When a properly collected, freshly voided specimen contains large numbers of bacteria, especially when accompanied by many white cells, it is usually indicative of a urinary tract infection. Bacteria are reported according to the number that is present (few, moderate, etc.), but no attempt is made, in the routine urinalysis laboratory, to identify the exact organism. The presence of bacteria is easily recognized when the sediment is viewed under high-power magnification (Fig. 5-52). 

Some bacteria reduce nitrate to nitrite, allowing for the detection of bacteria by chemical methods. However, not all pathogenic bacteria are nitrate reducers. In addition, conditions exist which influence the presence of nitrites. The presence of leukocytes may provide more accurate correlation with bacterial infection than does nitrite. YEASTYeast cells are smooth, colorless, usually ovoid cells with doubly refractile walls. They can vary in size and often show budding (Fig. 5-53). They may sometimes be mistaken for red cells, but unlike RBCs, they are insoluble in acid and alkali, and they will not stain with eosin. Yeast may be found in urinary tract infections, especially in patients with diabetes. Yeast may also be present in the urine as a result of skin or vaginal contamination. Candida albicans is the most common yeast to appear in the urine.16

CYLINDROIDS

Cylindroids resemble casts but have one end which tapers out like a strand of mucus. The exact site and mechanism of their formation are not known, but since they usually occur in conjunction with casts, they are considered to have the same significance.12,27 Separate classification of cylindroids from that of casts is no longer needed.36 Cylindroids are frequently hyaline, but like the one pictured in Figure 5-54, they may also incorporate other material.

SPERMATOZOA

Spermatozoa may be present in the urine of men after epileptic convulsions, nocturnal emissions, diseases of the genital organ, and in spermatorrhea. Sperm may also be found in the urine of both sexes after coitus. Spermatozoa have oval bodies and long, thin, delicate tails (Fig. 5-55).

Figure 5-52. Bacteria (rods, cocci, and chains) (500x)

Figure 5-53. Yeast cells. Note the budding and doubly refractile walls (1000x).

Figure 5-54. Cylindroid. Note the tapering tail (400 )

Figure 5-55. Spermatozoa (500 ).

MUCOUS THREADS

Mucous threads are long, thin, wavy threads of ribbonlike structures which may show faint longitudinal striations (Fig. 5-56). Mucous threads are present in normal urine in small numbers, but they may be very abundant in the presence of inflammation or irritation of the urinary tract.

Some of the wider threads may be confused with cylindroids or hyaline casts. Heavy mucous threads tend to incorporate WBCs. 

Figure 5-56. Mucous threads. Viewed with an 80A filter (100x)

OVAL FAT BODIES AND FREE FAT DROPLETS

Fat may be present in the urine as free droplets or globules, within degenerating or necrotic cells (oval fat bodies), or incorporated in a cast.

Oval fat bodies are usually defined as being renal tubular cells which contain highly refractile fat droplets (Fig. 5-57). They are either the result of the incorporation of fat that has been filtered through the glomerulus or they are renal tubular cells which have

Figure 5-57. Oval fat body and a fiber (500x).

undergone fatty degeneration. Oval fat bodies may also be macrophages or polymorphonuclear leukocytes that have either ingested lipids or degenerated cells, or have undergone fatty degeneration.

Lipids may also appear in the urine as free fat droplets (Fig. 5-58). These droplets frequently vary in size, since the fat globules can coalesce together. Fat droplets are  highly refractile, are globular in shape, and frequently have a yellow–brown appearance, although under low power and under subdued light they may sometimes appear to be black because of their high refractive index.

In lipiduria (the excretion of lipids in the urine), the free fat droplets may be found floating on the surface of the urine.

Figure 5-58. Fat droplets. Field also contains WBCs (500x)

Figure 5-59. Polarized anisotropic fat droplets. Note the “Maltese-cross” formation (160x)

Free-floating fat, or fat incorporated in a cell or cast, is composed of cholesterol esters or free cholesterol. This form of fat is anisotropic and will form “Maltese crosses” under polarized light (Fig. 5-59), but they will not stain with fat stain. If they consist of triglycerides, or neutral fat, they will not polarize but will stain with Sudan III or Oil Red O. Fat is not detected by chemical tests; therefore, microscopic examination for the detection of fat and oval fat bodies is necessary.

Anisotropic fat globules which manifest the “Maltesecross” formation are termed “doubly refractile fat bodies”. Fat may be present in the urine as the result of fatty degeneration of the tubules. It is frequently found in the nephrotic syndrome and may also be present in diabetes mellitus, eclampsia, toxic renal poisoning, chronic glomerulonephritis, lipoid nephrosis, fat embolism, and following extensive superficial injuries with crushing of the subcutaneous fat. Lipiduria may also occur following fractures of the major long bones or pelvis, and in multiple fractures in which fat may be released from the bone marrow into the circulation and then filtered through the glomerulus.  

REFERENCES 
Lillian A. Mundt and Kristy Shanahan, Graff's Textbook of Urinalysis and Body Fluids, Second Edition 2011