From the Guidelines
The workup for a three-year-old with calcium oxalate crystals in the urine should begin with a comprehensive history and physical examination, followed by specific laboratory and imaging studies, prioritizing the assessment of urinary tract infection, hypercalciuria, and family history of stone disease, as recommended by the American College of Radiology 1. The initial evaluation should include a thorough history, covering topics such as urinary tract infection, recent strep throat, recent trauma, and family history of sickle cell disease or hemophilia, as well as a physical examination to assess for signs of occult trauma, foreign body insertion, or genital or anal bleeding suggesting sexual abuse 1. Key laboratory studies should include:
- Urine analysis to evaluate for hematuria, proteinuria, and the presence of white cells and micro-organisms
- A spot urine calcium-to-creatinine ratio to assess for hypercalciuria
- Blood tests, including serum calcium, phosphorus, magnesium, creatinine, electrolytes, parathyroid hormone, and vitamin D levels A renal ultrasound is recommended to detect any stones or nephrocalcinosis, as it is the best modality to display the anatomy, size, and position of the kidneys, especially before biopsy 1. Dietary assessment is crucial, focusing on intake of high-oxalate foods, excessive vitamin C, and calcium consumption, and management typically involves increasing fluid intake, moderating dietary oxalate, ensuring adequate calcium intake, and limiting sodium and animal protein, as supported by the American College of Physicians 1 and the American Urological Association 1. In cases of hypercalciuria, thiazide diuretics like hydrochlorothiazide may be prescribed, and potassium citrate can be beneficial for hypocitraturia, as recommended by the American Urological Association 1. This comprehensive approach is necessary because calcium oxalate crystals may indicate underlying metabolic disorders that require early intervention to prevent kidney stone formation and potential kidney damage.
From the Research
Workup for Calcium Oxalate Crystals in Urine
For a three-year-old with calcium oxalate crystals in the urine, the workup should include:
- Analysis of stone composition by polarization microscopy 2
- Measurement of serum calcium, phosphate, uric acid, 1,25(OH)2D3, and creatinine 2
- Twenty-four-hour urine collection for analysis of volume, pH, and excretion of calcium, phosphorus, magnesium, uric acid, citrate, sodium, oxalate, and creatinine 2, 3, 4
Diagnostic Evaluation
The diagnostic evaluation should be conducted while the patient follows their usual diet 2. The evaluation may also include:
- Fourier transform infrared spectroscopy (FT-IR) to detect the ratio of calcium oxalate dihydrate (COD) and monohydrate (COM) crystals in stones 5
- Assessment of urinary metabolic risk factors, such as hypercalciuria, hyperoxaluria, and hypocitraturia 5, 6
Predicting Stone Composition
Twenty-four-hour urine analysis may predict urinary stone composition, with significant predictors including: