Renal tubular cells casts
The tubular
cells seen in casts are usually from the collecting tubes, but
cells originating from the proximal tubules or any other sections
(prior to the collecting tubes) of the nephron is possible. With
the PAP stain, Schumann subdivides renal tubular cell casts in
RTC cast and necrotic RTC casts. A very few hyaline RTC casts or RTC casts can occasionally be encountered in a healthy person's urinary sediment. In this context, these casts have no more clinical meanings than the hyaline casts. The renal tubular cell casts are not associated to a precise pathology, but are found in multiple conditions that affect the renal tubules. The RTC casts are non specific. Among pathologies associated with the presence of these casts let us mention: the acute interstitial nephritis, acute transplant rejection, and tubular necrosis. Necrotic RTC casts are seen in acute tubular necrosis and in nephrotoxic tubular diseases.
The typical renal tubular cell casts are described as hyaline matrix casts, showing two rows of well delimited tubular cells. The two rows criteria is not reliable because the white blood cell casts can also appear with this particularity. Sequestrated tubular cells in a hyaline matrix is possible, but studies on the subject seem to indicate that the majority of casts of this type are formed of cells fixed to the surface of the casts.
White blood cell casts
White blood cell casts in routine urinalysis refer to a hyaline matrix cast bearing neutrophil inclusions. This simplification is justified by the fact that the neutrophil is, by far, the most frequently seen cell in these casts. With a PAP staining, other leukocytes can be identified within WBC cast. Except for the lymphocytes, all the other leukocytes casts have been described in the literature. In our view, it is reasonable to think that this cast exists in certain clinical conditions. Plasma cell diseases, infiltrating the tubular interstitial tissue, can be expected to give lymphocytes casts.The neutrophil casts
For the
microscopist, the identification of white blood cell cast is
often a challenge. Casts of this type are often mixed and the
plurilobulate of cells is not always visible, even in phase
contrast. Because of the clinical significance of these casts, it
is necessary to make some identification efforts, like using
special stains. As for the distinction between the cellular casts
and the renal tubular cell fragments, it is sometimes difficult
to establish if we are dealing with a real leukocytes cast or
with a cluster of leukocytes distributed as a cast (pseudocasts).
The presence of a matrix is a criterion. White blood cell casts are found in renal diseases when the complement factor C3 is activated, thus generating an inflammation process. Pyelonephritis (cortex), acute allergic interstitial nephritis, and some glomerulonephritis are diseases activating the C3 factor.
The identification of the polynuclear cells is possible by the demonstration of specific enzymes. The Naphtyl AS-D chloro-acetate esterase is found in the granulocytes, the mastocytes, and in some macrophages. This staining method can demonstrate the presence of polynuclear cells sequestrated in a cast matrix (hyaline WBC cast). This method allows a much greater sensitivity toward the detection of white blood cell casts. With this high sensitivity, one can find a hyaline cast with only one or two leukocytes within the matrix. The problem is the clinical meaning of this otherwise undetected figure. Some think that this finding is significant and represents a low or a silent nephritis.
Bright field identification of unstained cellular casts is not an easy job. The two pictures shown are illustrating this difficulty. The use of the Naphtyl AS-D chloro-acetate esterase staining procedure has permited us to positively identify the first casts as an RTC cast and the second as a WBC cast.
RTC cast WBC cast
White blood cell cast stained with (Naphtyl AS-D chloro-acetate esterase)
Eosinophil casts
Urinary eosinophiluria (> 7% of WBC) is found in acute allergic interstitial nephritis and in other conditions. White blood cell casts containing eosinophils can exclude an extrarenal origin for the eosinophiluria. These eosinophil casts can be demonstrated with the Hansel stain. Unfortunately, the smear stain version has a low recuperation with casts. Cytospin specimen should be used. The acetate filter PAP staining method is also a good option.Monocyte casts
The presence of monocytes within casts has been demonstrated using the monoclonal antibodies of the FMC series. This finding is associated with acute allergic interstitial nephritis, and with rapidly progressive glomerulonephritis.Macrophage casts
Macrophages
containing casts is not a rare figure. The casts are often
reported as cellular casts. The main reason is due to the fact
that macrophages are rarely recognizable. These casts are
frequent in the urinary sediment of hepatic patient. In this
context, the cells are large (too large for RTC) and stained by
the bilirubin. Staining with the naphtyl AS-D chloroacetate
esterase method will demonstrate some large positive cells
definitively not leukocytes. The oval fat body casts are special. Identification of these cells is easy with the use of polarized light. The fat droplets are typically birefringent with a maltese cross interference pattern. Since oval fat bodies are often of macrophage nature, oval fat body casts are considered as special cases of macrophages casts.