proteinuria is a cardinal sign of diverse renal diseases and can result in foamy urine . foaming occurs because albumin has a soap - like effect that reduces the surface tension of urine.1 it is generally thought that foamy urine is an early sign of renal disease , and , thus , that patients with this condition should be further evaluated . a recent pubmed search recovered no articles describing the proportion of patients with foamy urine who also show clinically significant proteinuria or microalbuminuria . we propose that the apparent lack of studies on foamy urine is due to the absence of an accepted clinical definition for this condition . it is essentially impossible to arrive at a definition of foamy urine from subjective observations , although such data could provide a basis for designing objective research studies . we report here on a descriptive study that aimed to determine the proportion of patients with foamy urine who also exhibited overt proteinuria or microalbuminuria . our secondary objective was to determine the risk factors and comorbidities associated with true proteinuria . we reviewed the medical records of new patients who visited our nephrology clinic between 1 november 2011 and 30 april 2012 complaining of foamy urine . we defined a new patient as one who was visiting our hospital or clinic for the first time or one who had been lost to follow - up for more than 2 years . demographic data and medical history of diabetes mellitus ( dm ) , hypertension , ischemic heart disease , and hyperlipidemia were collected . in addition , a drug history was obtained of nonsteroidal anti - inflammatory drugs ( nsaids ) taken for more than 2 weeks before the visit to our clinic . we also obtained the following laboratory test data : a ) spot urinary protein - to - creatinine ratio ( pcr ) determined by protein assay with the 200 fr neo , sicdia m - tp kit ( toshiba ) and creatinine assay with the modular p / modular d , jaffe kinetic colorimetric assay ( roche ) ; b ) spot urinary microalbumin to creatinine ratio ( acr ) determined by albumin assay on the nephelometer bn - ii by using n antiserum to human albumin ( siemens ) and the creatinine assay described as above . in addition , we obtained data for blood urea nitrogen ( bun ) , serum creatinine ( cr ) , and serum uric acid , calcium , and phosphate . an estimated glomerular filtration rate ( egfr ) was calculated by using the ckd - epi formula ( http://www.hdcn.com/calc.htm).2 overt proteinuria ( spot urine pcr > 200 mg / g ) and microalbuminuria ( spot urine acr of 17 - 250 mg / g in males and 25 - 355 mg / g in females ) were diagnosed according to kdoqi clinical practice guidelines.3 pearson 's chisquared test or fisher 's exact test were used for categorical variables . simple logistic regression analysis was used for continuous variables . multiple logistic regression analysis was performed by using all variables that showed statistical significance in the single - variable analysis . we modified the model by using the wald test , log - likelihood comparison test , and akaike 's information criteria ( aic ) . the statistical packages used were version 2.15.0 from the r development core team ( 2012 ; foundation for statistical computing , vienna , austria , isbn 3 - 900051 - 07 - 0 ; http://www.r-project.org ) . except for age , data are expressed as meanssds or ses . statistical significance was defined as p0.05 or is expressed by 95% confidence interval ( ci ) . we reviewed the medical records of 1248 patients and identified 72 ( 6.3% ) patients complaining of foamy urine . there were 59 males , and their median age was 65.5 years ( range , 36 - 87 years ) . twenty - six patients ( 36.1% ) had dm , 52 ( 72.2% ) had hypertension , 16 ( 22.2% ) had ischemic heart disease , and 21 ( 29.2% ) had hyperlipidemia . eleven patients ( 15.3% ) had taken an nsaid for more than 2 weeks ( table 1 ) . laboratory findings were as follows : mean serum cr , 1.000.32 mg / dl ; egfr , 78.422.6 ml / min ; serum bun , 16.45.0 mg / dl ; serum uric acid , 5.51.5 mg / dl ; total serum calcium , 9.20.4 mg / dl ; serum phosphate , 3.20.5 mg / dl ; and serum glucose , 122.052.1 mg / dl . nine patients ( 12.5% ) had an egfr of less than 60 ml / min . sixteen patients ( 22.2% ) had overt proteinuria . in the single - variable analysis , dm ( and high serum glucose ) , poor renal function ( high cr , bun , low egfr ) , increased serum phosphate , and increased serum uric acid were associated with overt proteinuria ( tables 1 and 2 ) . serum phosphate and uric acid could be added to the regression model because they were significant in a wald test and a log - likelihood comparison . consequently , we established a regression model that consisted of dm , serum creatinine , uric acid , and phosphate . increased serum cr and increased serum phosphate showed a significant association with overt proteinuria for every 0.1-mg / dl increment of serum cr , the odds ratio ( or ) for overt proteinuria was 1.34 ( 95% ci : 1.05 - 1.80 , p=0.028 ) , and for every 1-mg / dl increment of serum phosphate , the or was 5.83 ( 95% ci : 1.22 - 41.0 , p=0.047 ) ( table 2 ) . we performed a subanalysis in 38 patients ( 31 males ) for whom acr results were available . thirteen patients ( 34.2% ) had dm , 23 ( 60.5% ) had hypertension , 7 ( 18.4% ) had ischemic heart disease , and 9 ( 23.7% ) had hyperlipidemia . laboratory findings were as follows : serum cr , 0.990.34 mg / dl ; egfr , 80.025.3 ml / min ; serum phosphate , 3.20.5 mg / dl ; and serum glucose , 128.463.3 mg / dl . five patients ( 13.2% ) showed an egfr of less than 60 ml / min ( table 3 ) . in this subgroup of 38 patients , 12 ( 31.6% ) showed microalbuminuria or overt proteinuria or both . dm , serum uric acid , and poor renal function were associated with proteinuria in the single - variable analysis ( table 3 , 4 ) . only serum cr showed a statistically significant association with proteinuria in the multiple logistic regression analysis ( the or was 1.42 for every 0.1-mg / dl increment , 95% ci : 1.01 - 2.34 , p=0.0889 ) ( table 4 ) . in patients without dm or hypertension , 11.8% ( 2/17 ) showed overt proteinuria and 23.1% ( 3/13 ) showed microalbuminuria or overt proteinuria or both . a textbook of nephrology describes " foamy urine " as a phenomenon that can be observed in patients with nephrotic syndrome.1 in the public mass media , experts in renal disease recommend that patients with foamy urine undergo a medical examination for renal function . in our data , twenty - two percent of patients complaining of foamy urine had overt proteinuria and 31.6% had microalbuminuria or overt proteinuria or both . although an english - language search of pubmed recovered no articles describing the clinical features of patients with foamy urine , we found one korean - language article that compared clinical features between patient groups with and without foamy uirne.4 in that study , there was no dipstick - positive proteinuria among 45 patients complaining of foamy urine . however , the authors did not perform any quantitative test for proteinuria , such as that done in the present study , so that it is difficult to conclude that those authors successfully determined the relationship between foamy urine and clinically significant proteinuria . in addition , the 45 subjects examined were healthy individuals who underwent the medical examination for a health promotion . second , foamy urine was identified through a questionnaire and was not the result of a complaint . clearly , patients complaining of foamy urine at a visit to their medical professional are more likely to have comorbidities . in this regard , our patients who complained of foamy urine visited the clinic voluntarily , and a considerable proportion had other medical problems . furthermore , when we expanded the definition of proteinuria to include microalbuminuria , the proportion of patients with foamy urine who also had clinically significant proteinuria increased . we therefore suggest that all patients who complain of foamy urine should undergo a quantitative test for urinary protein . as expected , an increased serum cr showed a statistically significant association with overt proteinuria . serum phosphate was also positively correlated with overt proteinuria , but this might be explained by the fact that phosphate levels are commonly increased in patients with poor renal function . in our data , serum phosphate and creatinine showed a very weak correlation ( r = 0.0457 , p = 0.72 ) . recently , it was reported that hyperphosphatemia is associated with overt proteinuria in nondiabetic patients with stage 3 to 5 chronic kidney disease.5 the relationship between serum phosphate , foamy urine , and overt proteinuria is uncertain at present , and therefore data from more patients will be required to examine this fully . the main limitation of our study is that we restricted our patient group to those with subjective foamy urine and we did not incorporate any objective definition of this condition . presently , foamy urine is detected only by the patient ; thus , it is very difficult to interpret data on foamy urine objectively . for example , parameters such as how long the foam persists and how thick the foam appears will require analysis . although there are difficulties in objectively defining foamy urine , the fact that a significant number of patients with foamy urine also showed clinical proteinuria suggests that such a definition should be established . as a result , there are some concerns about the integrity of our data , which were collected by a retrospective medical record review . in addition , for this study , the retrospective data collection reduced the statistical power of our risk analysis . to minimize these limitations , we reviewed the medical records of new patients only . clearly , the low statistical power of such a study can be overcome by increasing the number of individual medical records included . in summary , among the patients who complained of foamy urine , a considerable number also showed overt proteinuria . in addition , increases in serum creatinine and serum phosphate showed a statistically significant association with overt proteinuria . we suggest that a quantitative test for proteinuria should be performed on all patients complaining of foamy urine .
foamy urine is widely regarded as a sign of proteinuria . however , there is no objective definition of foamy urine and there are no reports on the proportion of involved patients who have overt proteinuria or microalbuminuria . 
 we performed this study to investigate this proportion and to identify possible risk factors for these two conditions . 
 we reviewed all new outpatients from 1 november 2011 to 30 april 2012 and identified patients complaining of foamy urine . 
 their demographic data and medical records were examined . in particular , we tabulated the patients ' spot urinary protein to creatinine ratio , spot urinary microalbumin to creatinine ratio ( acr ) , blood urea nitrogen ( bun ) , and serum levels of creatinine ( cr ) , uric acid , calcium , phosphate , and glucose . 
 in addition , we calculated estimated glomerular filtration rates ( egfrs ) by using the ckd - epi equation . 
 we also performed risk factor analysis with the chi - squared test and by logistic regression . 
 seventy - two patients ( 6.3% of total new outpatients ) complained of foamy urine ; of these , there were 59 males with a median age of 65.5 years ( range , 36 - 87 years ) . 
 of the 72 patients , 16 ( 22.2% ) had overt proteinuria . 
 we found that diabetes , poor renal function ( high cr , bun , low egfr ) , increased serum phosphate , and increased serum glucose were associated with overt proteinuria . 
 multiple logistic regression analysis showed that serum cr and serum phosphate were associated with overt proteinuria . 
 the acr was available for 38 patients , and in this subgroup , 12 ( 31.6% ) showed microalbuminuria or overt proteinuria . in this subgroup , 
 a high serum cr was the only statistically significant risk factor . among patients who complained of foamy urine 
 , approximately 20% had overt proteinuria , and increased serum cr and phosphate were statistically significant risk factors .