Nephrolithiasis is a common cause of morbidity recently. Studies have shown that metabolic causes of nephrolithiasis were hypercalciuria, hypocitraturia, high or low pH of urine, hyperuricosuria, hyperoxaluria, hypomagnesaemia and cystinuria.

Hypocitraturia is seen almost 30% of patients with nephrolithiasis. The importance of citrate in nephrolithiasis stems from the recognition that citrate is a direct inhibitor of calcium phosphate precipitation ¹ and the generation of calcium oxalate crystal ². The ability of citrate to form soluble complexes with divalent cations, such as calcium, is well known. Such complexation may cause some reduction in the urinary saturation of “stone-forming” calcium salts. For these reasons urinary citrate concentrations may have important rolls in renal stone formation. It has also been shown that four of every five patients with nephrolithiasis were male ³. One of the problems with citrate excretion is that it depends on age and sex; it changes with age ⁴ and is generally higher in women than in man ^4-9.

Urine analysis is important in determining urine pH, eliminating probable infection, and the most importantly learning the type of crystals (crystals usually seen during the acute attack). Concentrations of serum electrolytes, calcium, phosphate, creatinine and uric acid have to be measured at the first biochemical investigation of patients with nephrolithiasis. In addition, 24-hour urine volume, creatinine, urea, Na⁺, Ca⁺⁺, phosphate, uric acid, oxalate, citrate, urine pH, and serum level of Intact Para Thyroid Hormone (IPTH) may be assessed.

The purpose of this study was to find out the relation between urine and serum parameters that are measured routinely in patients with nephrolithiasis. Then more clarify formation of nephrolithiasis.

Our study was held in Medical Faculty of Gazi University, Department of Medical Biochemistry, and Central Laboratory on January, February and March in 2004. One hundred fortythree of the patients with nephrolithiasis were male and eightyeight of them were female, and mean ages were 42.6±12.4 years and 43.4±15.1 years respectively. Whether the patients had nephrolithiasis or not confirmed with each patient’s data. The results of analysis of urine oxalate, citrate, uric acid, calcium, phosphate and magnesium, pH of 24 hour urine; serum uric acid, calcium, phosphate and IPTH were reviewed retrospectively.

Urine volume and levels of citrate, oxalate, calcium, creatinine, urea, Na⁺, Ca⁺⁺, phosphate, uric acid were measured. Serum electrolytes, calcium, phosphate, creatinine and uric acid levels were also determined. Urinary citrate and oxalate levels were measured spectrophotometrically with enzymatic method by means of using commercially available diagnostic kits (Roche Diagnostics, Darmstadt, Germany and Sigma, St Louis, MO; respectively). Levels of other parameters were measured using Abbott-Aeroset autoanalyzer (USA). IPTH was measured with Abbott Architect 2000 chemiluminescence immunoassay analyzer (USA).

Statistical Analysis:
The results are presented as mean±SD, student’s t-test was used for statistical analysis. Pearson test was used for correlation analysis. p values <0.05 were regarded as statistically significant.

The mean values of urinary and serum parameters were shown in Table 1 and 2 respectively. Metabolic analysis showed that in patients with nephrolithiasis 24-hour urine volume, and urinary magnesium and oxalate excretion were higher than normal intervals. The other measured parameters were at normal levels. Although urine excretions of calcium, uric acid were significantly greater in men, excretion of citrate was significantly lower in men.

Table 1: 24-Hour Urinary Excretions of Constituents

Table 2: Values for Serum Chemistry Tests and PTH

As a result of correlation analysis, significant correlations were found between: both urine and serum levels of creatinine with both urine and serum levels of uric acid [r= 0.70 (p<0.01), r= 0.55 (p<0.01) respectively]; urine levels of phosphorus with urine levels of urea [r=0.99 (p<0.01)]; urine levels of uric acid with urine levels of calcium [r=0.48 (p<0.01)] and between urine levels of chlorine with uric acid [r= 0.54 (p=0.00)] and creatinine [r= 0.59 (p<0.01)]. These strong relationships were shown in figure 1.

Figure 1: Relationship Between 24-Hour Urinary and Serum Biochemical Parameters
a) Urine levels of creatinine with urine levels of uric acid
b) Serum levels of creatinine with serum levels of uric acid
c) Urine levels of uric acid with urine levels of calcium
d) Urine levels of chlorine with urine levels of uric acid
e) Urine levels of chlorine with urine levels of creatinine

We investigated the correlations between each parameters of 24-hour urine assessed ordinary in patients with nephrolithiasis. In our study we found a different aspect of biochemical values in nephrolithiasis.

It is known that while the raised excretion of oxalate, uric acid, calcium and phosphorus in the urine increase the formation of nephrolithiasis; raised excretion of citrate, magnesium, albumin and alkali urine decrease this process. In our patients with nephrolithiasis the levels of urine citrate, calcium, uric acid, phosphorus, sodium (up limit in men), potassium, chlorine and creatininee were within normal limits but the levels of 24-hour urine volume, and urinary magnesium and oxalate excretion were higher than normal.

Several reports claim that idiopathic stone formers excrete significantly less citrate in their urine than normal subjects ^5-7,9-15. Others, however, have not confirmed this difference ^16-19. One of the problems with citrate excretion is that it depends on age and sex; it changes with age ⁴ and is generally higher in women than in man ^4-9. Our results were in agreement with this data.

The levels of all serum parameters were within normal intervals but only IPTH was higher than normal in female patients. Primary hyperparathyroidism is related with stone formation in patients with nephrolithiasis. We also observed positive correlations between urine and serum levels of creatininee with urine and serum levels of uric acid; urine levels of phosphorus with urine levels of urea; urine levels of uric acid with urine levels of calcium and among the urine levels of chlorine with uric acid and creatinine.

Either Fellstrom et al. ²⁰ in patients (n= 467) with calcium lithiasis or Dumoulin et al. ²¹ in patients (n= 49) with pure and mixed CaOx (calcium-oxalate) lithiasis found out a positive correlation between urine values of uric acid and oxalate. Although Duranti et al. in patients (n= 30) with calcium lithiasis found a positive correlation between urine values of calcium and phosphorus, they did not find correlation among creatininee, uric acid, urea, chlorine and magnesium excretions ²². Futhermore Conta A et al. ²³ and Welshman et al. ⁴ in patients with CaOx lithiasis found that patients with hypocitraturia also had hypercalciuria. But Menon and Mahle described no significant correlation between calcium and citrate excretion in their controls or patients with stone ¹⁴. As a different relationship Oehlschlager et al. ²⁴ found a combination of hypercalciuria and hyperoxaluria in patients (n= 22) after extracorporeal shock wave lithotripsy treatment. Both Tefekli A et al. and Ogava Y et al. found that levels of urine calcium were higher in patients with CaOx stones than normal patients; level of urine citrate, magnesium and creatinine were lower than normal (n= 155 and n= 222) ^25,26, but Scholz et al. ²⁷ found out that concentrations of magnesium, uric acid and phosphate were within normal limits in urine. These different results may result from the special characteristics of a particular region (diet, climate, genetics, socio-economic factors, etc.). The dietary differences may be the most important factor to explain the deviation among the various studies.

In conclusion, it is obvious that there are correlations among some urine parameters and this may be clinically useful for a more effective treatment planning.