Renal casts II

Content

There is no widely accepted rules for the cast nomenclature. The names used to report casts should consider the following facts.

Facts.

There is no segregation process in cast formation. The direct consequence is that many ( if not most) casts are of mixed inclusions.

On the routine report forms, the space allowed for writing the unusual element is often limited. Report for a routine microscopy should be precise and as short as possible.

Some distinctions must be adapted to the type of examination. Without a special staining method, the names chosen must be sufficiently large and adapted to the identification possibilities. For example, the cellular cast is an unprecise term, but it is suited for bright field unstained specimen.

Distinctions must be adapted to the clinical significance. Convoluted casts are spectacular, but this format has never been related to a clinical condition. Distinction based on visual differences, and without clinical significance, should be discarded.

Rule of third

It has been proposed that, if more than one third of a cast is filled with an element, then the cast takes the name of the element. On the opposite the term "hyaline ..element cast" should be used. This term should be used with care since it could be interpreted by some as a less pathological cast, which is really not the case. Using the term hyaline..element in a report, where there is also mentioned, the "element cast", should be avoided. Reporting "hyaline element cast" and "element casts" one the same report gives a longer report without any benefit to clinical significance. In this context, the report should mention hyaline casts and element casts.

Mixed cast

As mentioned earlier, there is no segregation mechanism in cast formation. Many casts are made of mixed elements. Some use the term "mixed element1-element2" to report these casts. The term mixed, without further precision, should not be used since it says nothing. Care should be taken with the mixed casts in routine urinalysis; the report must not look like a grocery list. An easy way to overcome this potential problem, is to split the mixed cast into its element and reporting two casts; element1 casts, and element2 casts. This solution as the advantage of shortening reports without any loss of clinical significance.

Cast matrix

The casts seen in the urinary sediment can be made of a typical hyaline or a typical waxy matrix. But many casts have a matrix that seems to be an intermediate between these two. Casts having a different matrix at one end are not rare. To our view, the cast matrix can vary from the perfectly hyaline to the perfectly waxy. The matrix type is the result of the intratubular maturation time. A cast evacuated shortly after is formation will have a hyaline matrix. A cast remaining for a long period in the nephron will have a waxy appearance. This situation is encountered in conditions of low urine flow. Waxy casts were at a time called renal failure casts. From this view, any element cast can have a hyaline to waxy matrix. Usually the term "waxy" is reserved to the typical waxy cast.

The hyaline matrix

The hyaline matrix is by far the most frequently observed. Hyaline casts, that is hyaline matrix casts without inclusion, are seen in numerous conditions. Some of these conditions are the results of a pathological process, but many are results of a normal physiological activity. Hyaline casts can be seen after a strenuous exercise. Hyaline casts are considered as physiological casts. A count of 1000 or less hyaline casts in a 24-hour specimen is a normal value.

Lindner has demonstrated changes in the aspect of the hyaline cast, in time ordered specimens, after a strenuous physical exercise. Shortly after exercise, the first hyaline casts «Early» seen are difficult to see in bright field microscopy. These are more easily observed in phase contrast microscopy. Under scanning electron microscope "SEM", these have an empty appearance. These casts are believed to be in an unstabilized state, making them readily soluble. The second type are the «"Typical"» hyaline casts. Compared to the early form, the typical hyaline casts have a homogeneous filled structure. These casts are in a stabilized state less subject to dissolution. The third form is the «Wrinkled» hyaline casts. This type has a wrinkled matrix, probably due to unequal internal tension within the matrix. The last form observed in the experiment is the «convoluted» hyaline casts. It seems that this form is due, again, to internal tensions creating a helix like structure.

Variations in shape and texture of the hyaline casts are, for the moment, of no clinical value.

Types of hyaline casts after a strenuous exercise

Name	Time	Aspect	Example
«Early» hyaline cast	1 hour	empty (SEM)
«Typical» hyaline cast	3 hours	filled (SEM)
«Wrinkled» hyaline cast	5 hours	wrinkled (SEM)
«Convoluted» hyaline cast	12-24 hres	convoluted

The waxy matrix

The waxy casts owe their name to the opaque waxlike matrix. Waxy casts have square ends and have frequent notch like cracks perpendicular to the long axis. This matrix is related to a long period urinary stasis affecting some nephrons. Waxy casts are usually without inclusion or slightly granular, but waxy casts with inclusions are occasionally seen. An example of a waxy cellular cast is shown in this link pictures collection. We think that all the inclusions seen in a hyaline matrix are possible within the waxy matrix.

To our view, waxy casts represent a long time maturation of the convoluted cast. With time, the matrix gets more dense and proteins are added, resulting in typical waxy matrix.

The clinical meaning of a waxy-element cast is dictated by the element and not by the matrix, and should be reported as an element cast. The term waxy cast is reserved to the typical inclusion-free or slightly granular waxy casts.

Format

Lenght

short cast Casts can be seen as short, normal, or long. No clinical value is accorded to the length of the casts. Short, square ends, hyaline, or finely granular casts are occasionally seen in patients in a coma.

Width (The large cast)

cyl. large Casts can be classified, on a width basis, as normal, enlarged and large. Enlarged casts (1.5 x normal) are formed in a dilated tubule. In acute tubular necrosis of ischemic origin, casts are frequently enlarged. Enlarged casts should not be confused with the true large casts.

The large casts are usually related to a chronic renal failure state. In this specific situation, the remaining functional nephrons try to take over. These will have an oversized glomerule and large tubules. Casts formed in these nephrons have a width of four to ten times the normal size. The large waxy casts were, at a time, called the end stage renal failure casts.

Large casts should be reported as large .... cast

Shape

contouné A cast, hyaline or waxy, can presents itself as straight or convoluted. As already mentioned, the shape is due to tensions within the matrix. The shape is not related to any clinical condition and should be disregarded.