Can hyperoxaluria be diagnosed by urine routine and microscopy?

From the Guidelines

Hyperoxaluria cannot be definitively diagnosed by routine urinalysis and microscopy alone. While routine urinalysis may detect calcium oxalate crystals in the urine, which can suggest hyperoxaluria, this finding is not specific or sensitive enough for a definitive diagnosis 1. The proper diagnosis of hyperoxaluria requires a 24-hour urine collection to measure oxalate excretion, with values exceeding 0.46 mmol/24 h being diagnostic, and this value should be corrected for body surface area to 1.73 m2 to enable interpretation of pediatric results using the adult reference range 1.

Key Points to Consider

• Routine urinalysis may raise suspicion of hyperoxaluria but is not sufficient for a definitive diagnosis
• A 24-hour urine collection is necessary to measure oxalate excretion accurately
• Values exceeding 0.46 mmol/24 h are considered diagnostic for hyperoxaluria
• Additional tests such as serum chemistry panels, genetic testing, and kidney imaging or biopsy may be necessary for comprehensive diagnosis and management
• The presence of calcium oxalate crystals in urine can be due to various reasons and is not exclusive to hyperoxaluria

Diagnostic Approach

According to the clinical practice recommendations for primary hyperoxaluria, suspicion of PH in a patient with normal kidney function should be investigated initially by measurement of urine oxalate in a 24 h urine sample 1. It is also recommended that at least two positive urine assessments (urine oxalate higher than the upper reference limit) should be used to establish hyperoxaluria 1.

Special Considerations

In cases where 24-hour urine collections are inconvenient, a random urine sample can be used for preliminary analysis, but it must be normalized to urinary creatinine level, and acidification of such samples can be carried out in the laboratory provided the sample is kept at 4 °C after collection 1. The use of age-related reference values is recommended when interpreting urinary oxalate-to-creatinine ratios 1.

From the Research

Diagnosis of Hyperoxaluria

Hyperoxaluria can be a challenging condition to diagnose, and various methods are employed to identify and distinguish between primary and secondary hyperoxaluria.

• The diagnosis of hyperoxaluria typically involves the measurement of urinary oxalate excretion, which can be performed through 24-hour urine collections 2, 3.
• Urine routine and microscopy may not be sufficient for the diagnosis of hyperoxaluria, as they may not provide accurate measurements of urinary oxalate excretion 4, 5.
• Additional diagnostic tests, such as plasma oxalate levels, genetic studies, and liver biopsy, may be necessary to confirm the diagnosis and distinguish between primary and secondary hyperoxaluria 4, 6.
• A dietary survey and the measurement of lithogenic and stone-inhibitory substances in urine may also be helpful in diagnosing secondary hyperoxaluria 3.

Diagnostic Challenges

• The diagnosis of hyperoxaluria can be delayed, and the prognosis is often poor if left untreated 5.
• Primary and secondary hyperoxaluria have distinct clinical expressions, and a clear distinction between the two is essential for optimal treatment 3, 4.
• The measurement of urinary oxalate excretion can be influenced by various factors, including dietary intake and intestinal absorption, which can make diagnosis challenging 2, 3.

Importance of Accurate Diagnosis

• Accurate diagnosis of hyperoxaluria is crucial for optimal management and treatment, as different types of hyperoxaluria require different therapeutic approaches 4, 5.
• Prompt recognition and treatment of hyperoxaluria can improve outcomes and prevent complications, such as kidney damage and systemic oxalosis 5, 6.