From the Guidelines
Hyaline casts are a common finding in urine and do not necessarily indicate kidney damage, but their increased presence warrants further investigation, especially when accompanied by other abnormal urinary findings, such as proteinuria, dysmorphic RBCs, cellular casts, or renal insufficiency, which may require referral to a nephrologist for evaluation of medical renal disease 1. When evaluating patients with hyaline casts, it is essential to consider the clinical context and the presence of other urinary abnormalities. Hyaline casts are cylindrical structures found in urine that form when protein precipitates in the renal tubules and takes on the shape of the tubular lumen. They appear colorless, transparent, and homogeneous under microscopic examination.
- Hyaline casts are the most common type of urinary cast and may be present in small numbers (0-2 per low-power field) in normal urine, especially after strenuous exercise or dehydration.
- Increased numbers of hyaline casts often indicate conditions that cause proteinuria or reduced renal blood flow, such as fever, congestive heart failure, dehydration, strenuous exercise, and early stages of kidney disease.
- Hyaline casts are composed primarily of Tamm-Horsfall mucoprotein, which is secreted by the cells of the thick ascending limb of the loop of Henle. According to the AUA/SUFU guideline, patients with proteinuria, dysmorphic RBCs, cellular casts, or renal insufficiency may have medical renal disease, which can cause hematuria, and should be referred to a nephrologist for evaluation 1.
- Risk-based urologic evaluation should still be performed in these patients to identify coexistent urologic pathology. Proper hydration can help reduce hyaline cast formation in cases related to dehydration or exercise.
- Clinicians should refer patients with suspected medical renal disease for nephrologic evaluation, while still performing risk-based urologic evaluation 1.
From the Research
Definition and Detection of Hyaline Casts
- Hyaline casts are a type of cast found in urinary sediments, useful in identifying kidney diseases 2
- They can be detected in patients with normal renal function, and their presence may indicate increased plasma brain natriuretic peptide (BNP) levels 2
- The detection of hyaline casts can be performed through urine sediment analysis, and their morphology can be examined using staining techniques such as H/E and light chain immunofluorescence 3
Composition and Formation of Hyaline Casts
- Hyaline casts are composed of protein-protein aggregates, including histones and cathepsin B, in addition to light chains produced by malignant clones of plasma cells 3
- The formation of hyaline casts involves the aggregation of light chains, which can be either monomeric or dimerized, with dimerized light chains being more typical of lambda paraproteins 3
- The composition and formation of hyaline casts can vary depending on the type of light chain associated with the cast, with lambda light chains showing a higher ratio of dimerized to monomeric forms 3
Clinical Significance of Hyaline Casts
- The presence of hyaline casts in patients with normal renal function may indicate increased plasma BNP levels, which can be a marker of cardiovascular disease 2
- The detection of hyaline casts can be useful in identifying patients with kidney diseases, such as cast nephropathy and renal AL-amyloidosis, associated with monoclonal gammopathy of renal significance and multiple myeloma 3
- However, the clinical significance of hyaline casts in patients with early (stage 1 to 3) non-diabetic chronic kidney disease is uncertain, and further research is needed to determine their role in this context 4