From the Guidelines
The presence of calcium oxalate in the microscopic urine analysis of an 88-year-old female patient with impaired renal function indicates a risk for kidney stone formation, and she should increase her daily water intake and limit foods high in oxalate to prevent stone formation. The patient's age and impaired renal function put her at a higher risk for complications from kidney stones, and therefore, it is crucial to take preventive measures. According to the study by EN Taylor and GC Curhan 1, increasing dietary calcium intake can actually reduce the risk of stone formation by binding dietary oxalate in the gut. However, it is essential to maintain adequate calcium intake through diet rather than supplements, as supplemental calcium may increase the risk of stone formation, especially if taken between meals 1.
The patient should aim to increase her daily water intake to 2-3 liters, unless contraindicated by heart or kidney conditions, to dilute the concentration of calcium and oxalate in the urine. She should also limit foods high in oxalate, such as spinach, rhubarb, chocolate, nuts, and tea, as these can increase the risk of stone formation. A follow-up with her physician is recommended to evaluate for underlying causes like urinary tract infections, metabolic disorders, or medication effects. If the patient experiences flank pain, blood in urine, or difficulty urinating, she should seek medical attention promptly as these may indicate stone formation or movement.
It is also important to note that the American College of Physicians recommends management with increased fluid intake and pharmacologic monotherapy with a thiazide diuretic, citrate, or allopurinol to prevent recurrent nephrolithiasis in patients with active disease in which increased fluid intake fails to reduce the formation of stones 1. However, the patient's impaired renal function should be taken into consideration when deciding on the best course of treatment.
In terms of dietary changes, the patient can refer to Table 2 in the study by EN Taylor and GC Curhan 1, which provides dietary prescriptions for calcium stone prevention according to urinary risk factors. For example, if the patient has high oxalate levels, she should avoid high-oxalate foods and maintain adequate dietary calcium intake.
Overall, the patient should work closely with her physician to develop a personalized plan to prevent kidney stone formation and manage her impaired renal function.
From the Research
Presence of Calcium Oxalate in Urine Analysis
The presence of calcium oxalate in the microscopic urine analysis of an 88-year-old female patient with impaired renal function may indicate several underlying conditions.
- Calcium oxalate nephrolithiasis is a common syndrome that can recur and may be complicated by infection, obstruction, bleeding, and impairment in renal function 2.
- The formation of calcium oxalate stones depends on the state of urinary supersaturation with respect to calcium and oxalate, and the action of urinary inhibitors of crystal nucleation, aggregation, and growth 2.
Metabolic Disorders and Stone Formation
The study of female patients with calcium oxalate urolithiasis revealed that most stones comprised calcium oxalate monohydrate or mixtures of calcium oxalate dihydrate and hydroxyapatite 3.
- The most frequent abnormalities identified were hypocitraturia and hypercalciuria, with 90% and 45% of patients exhibiting these conditions, respectively 3.
- The daily secretion of citrate and oxalate in patients older than 50 years was significantly lower than in younger patients 3.
Clinical and Metabolic Correlates of Calcium Oxalate Stone Subtypes
The comparison of clinical and metabolic findings in calcium oxalate stone formers revealed differential underlying metabolic abnormalities associated with each subtype 4.
- COM (calcium oxalate monohydrate) formers exhibited higher rates of hypocitraturia and hyperoxaluria, while COD (calcium oxalate dihydrate) formers had significantly higher rates of hypercalciuria 4.
- Multivariate analysis found hypercalciuria to independently predict COD and hyperoxaluria to predict COM stones 4.
Hyperoxaluria in Idiopathic Calcium Oxalate Kidney Stone Disease
The investigation of urinary excretion of oxalate, calcium, and urate in patients with idiopathic calcium oxalate stone disease revealed that hyperoxaluria is a frequent finding in this condition 5.
- Defining hyperoxaluria as urinary oxalate excretion greater than 2 SD above normal, 50% of stone-forming people were found to be hyperoxaluric 5.
Mechanism of Calcium Oxalate Renal Stone Formation
The formation of calcium oxalate stones tends to increase with age and begins from the attachment of a crystal formed in the cavity of renal tubules to the surface of renal tubular epithelial cells 6.
- In individuals with hyperoxaluria or crystal urine, renal tubular cells are injured, and crystals easily become attached to them, leading to stone formation 6.