Relationship of proteinuria and albuminuria to posture and to urine collection period

Body mass index and albumin levels are prognostic factors for long-term survival in elders with limited performance status

Elderly long-term care facility residents typically have musculoskeletal conditions that may lead to long-term disability and increased mortality. Our main objective was to explore the relationship between body mass index (BMI), albumin levels, and mortality in elderly individuals with limited performance status. Among 182 participants (mean age, 78.8 years; 57% women), 11%, 64%, and 25% had serum albumin levels of <2.8, 2.8-3.5, and >3.5 g/dL, respectively. After multivariate adjustments, diastolic blood pressure >90 mmHg was associated with all-cause mortality [hazard ratio (HR) = 2.08, 95% confidence interval (CI) = 1.13-3.82; P = 0.018]. In addition, BMI <18.5 kg/m2 and albumin level <2.8 g/dL associated with higher mortality than BMI = 18.5-24 kg/m2 and albumin level > 3.5 g/dL (HR = 1.80, 95% CI = 1.11-2.94 and HR = 2.54, 95% CI 1.22-5.30, respectively; P = 0.018 and 0.013, respectively). Highest mortality was noted in participants with albumin levels <2.8 g/dL and BMIs <18.5 kg/m2 (HR = 6.12, 95% CI = 1.85-20.21, P = 0.003). Combined hypoalbuminemia (albumin level < 2.8 g/dL) and low BMI (<18.5 kg/m2) may be a useful prognostic indicator of high mortality risk in elderly individuals with limited performance status.

Urinary albumin excretion in healthy adults: a cross sectional study of 24-hour versus timed overnight samples and impact of GFR and other personal characteristics

Background

Urinary albumin can be measured in 24 h or spot samples. The 24 h urinary albumin excretion rate is considered the gold standard, but is cumbersome to collect. Instead, often an overnight sample is collected, and adjusted for dilution. Proxies for 24 h excretion rate have been studied in diabetics, but seldom in healthy individuals. Our aims were to compare 24 h and overnight albumin excretion, to assess the impact of personal characteristics, and to examine correlations between the 24 h excretion rate and proxies such as the albumin to creatinine ratio (ACR).

Methods

Separate 24 h and overnight urine samples were collected from 152 healthy kidney donors. Urinary creatinine, specific gravity, collection time, and sample volume determined. Differences between 24 h and overnight samples were examined, and the effects of age, sex, smoking, body mass, glomerular filtration rate, and urinary flow rate were assessed.

Results

The 24 h albumin excretion rate and ACR were both significantly higher than their overnight counterparts. Unadjusted albumin was unsurprisingly higher in the more concentrated overnight samples, while concentrations adjusted for specific gravity were similar. In multivariate analysis, the 24 h excretion rate and proxies were positively associated with glomerular filtration rate, as was ACR in overnight samples. There were positive associations between urinary albumin and body mass.

Conclusions

Proxies for the 24 h albumin excretion rate showed relatively high correlations with this gold standard, but differences due to sampling period, adjustment method, and personal characteristics were large enough to be worth considering in studies of albumin excretion in healthy individuals.

Renal parenchymal thickness and urinary protein levels in patients with ureteropelvic junction obstruction after nephrostomy placement

OBJECTIVE

To assess recovery of renal parenchymal thickness and urinary protein levels in patients with severely hydronephrotic kidneys after nephrostomy placement.

METHODS

Fourteen patients (median age 1 year, range 6 months-7 years) who underwent nephrostomy placement for unilateral ureteropelvic junction obstruction at our hospital between May 2007 and January 2009 were included in a retrospective analysis. All patients had severe hydronephrosis, with a median parenchymal thickness of 1.8 mm (range 1-2.5 mm). Kidney morphology was examined by ultrasound before the procedure and 1, 2, 3, 4, 6 and 8 weeks after. Urinary proteins (including albumin, immunoglobulin [IgG], alpha2-macroglobulin, alpha1-microglobulin, beta2-microglobulin [beta2-MG] and kappa chain) and creatinine levels were also tested during these follow-up visits. Fifteen healthy children were assessed for urinary protein levels as well and made up the control group.

RESULTS

Parenchymal thickness increased within 4 weeks of nephrostomy placement. Kidney volumes were significantly decreased within 2 weeks. No further changes in morphology were detected after 4 weeks. Urinary alpha1-microglobulin and beta2-MG levels decreased to baseline within 1 and 4 weeks, respectively. Urinary albumin, IgG, alpha2-macroglobulin and kappa chain levels decreased gradually after nephrostomy, but did not return to baseline within 8 weeks.

CONCLUSIONS

After nephrostomy placement, parenchymal thickness increases within 4 weeks, tubular function returns to normal earlier than glomerular function and glomerular membrane repair is inversely correlated with the severity of damage.

Importance of low-grade albuminuria

The well-described association between chronic kidney disease and cardiovascular disease is typically thought to originate from loss of renal function, as estimated by the glomerular filtration rate. However, recent data suggest that urinary albumin excretion has an important role in this association. Albuminuria is a marker of underlying vascular dysfunction and has been correlated with structural and functional integrity of the vasculature. Although the traditional upper limit of normal daily albumin excretion has been 30 mg/d, recent epidemiologic data suggest that levels in the general population are actually much lower. Further, within this range of low-grade albuminuria (LGA), increasing excretion rates are associated with increasing risk of cardiovascular disease. This association is independent of renal function, and in the earliest stages of chronic kidney disease, LGA seems to be a more important determinant than the glomerular filtration rate. This emerging association underscores the complexity of albumin excretion, in which subtle changes in albumin excretion reflect widespread vascular processes. Using the key words albuminuria, low-grade albuminuria, and microalbuminuria in a PubMed search of literature from January 1, 1995, to February 29, 2008, this review summarizes the most recent data on LGA and its association with cardiovascular and renal disease.

Microalbuminuria and hyperthermia independently predict long-term mortality in acute ischemic stroke patients

OBJECTIVES

To investigate the association between microalbuminuria (MA) and hyperthermia in acute ischemic stroke and to evaluate their significance as the predictors of long-term mortality after stroke.

MATERIAL AND METHODS

We assessed neurologic deficit, urinary albumin excretion and body temperature in 60 patients admitted within 24 h after the onset of their first ischemic stroke. Outcome was assessed by 90-day and 1-year mortality.

RESULTS

MA was found in 46.7% of patients. Hyperthermia was found in 18.3% patients on Day 1 and in 25% patients on Day 2. The correlation between albuminuria on Day 2 and the body temperature on Days 1 and 2 was found (r = 0.45, and r = 0.30, respectively; both P < 0.05). The mortality was significantly higher in the group of patients with both MA and hyperthermia on Day 2 (73% vs 10% after 90 days; P < 0.0001 and 73% vs 18% after 1 year, P < 0.005). In the logistic regression analysis, albuminuria (P = 0.017), hyperthermia on Day 1 (P = 0.028) and neurologic deficit on admission (P = 0.044) independently predicted 1-year mortality after ischemic stroke.

CONCLUSION

Daily urinary albumin excretion correlates with the body temperature in acute stroke patients, but the predictive power of both these variables is independent of that association.

Microalbumin measurement alone or calculation of the albumin/creatinine ratio for the screening of hypertension patients?

BACKGROUND

Spot urine sampling seems to be a reliable screening method for the detection of microalbuminuria in hypertensive patients. It remains unclear whether microalbumin measurement alone or calculation of the albumin/creatinine ratio (ACR) are more reliable for the detection of microalbuminuria in non-selected hypertensive patients.

METHODS

Following collection of a spot, midstream urine sample, urine was collected for 24 h for the measurement of microalbumin in 264 hypertensive patients. We compared microalbumin concentration in the spot urine with microalbumin measured in the 24-h urine sample and examined the utility of the ACR in evaluating microalbuminuria in hypertensive patients. Pathologic microalbuminuria was assumed when the microalbumin concentration exceeded 30 mg/l in the 24-h urine sample. Diagnostic performance is expressed in terms of specificity, sensitivity, positive (PPV) and negative predictive value (NPV), and area under receiver operating characteristics curve (AUC).

RESULTS

A total of 47 samples (17.8%) showed pathologic microalbuminuria in the 24-h urine sample. The diagnostic performance expressed as AUC was 0.94 (95% CI 0.90-0.98) for microalbumin measurement alone and 0.94 (95% CI 0.89-0.97) for ACR. The PPV and NPV were 44.2 and 97.9% for microalbumin measurement alone. ACR revealed a PPV of 29.3% and a NPV of 96.2% for males and 42.9 and 98% for females, if a cut-off value of 2.5 mg/mmol for males and of 4.0 mg/mmol for females was used.

CONCLUSIONS

The ACR did not provide any advantage compared with microalbumin measurement alone, but requires an additional determination of creatinine and the use of gender-specific cut-off values. Therefore, measurement of microalbuminuria alone in the spot urine sample is more convenient in daily clinical practice and should be used as the screening method for hypertensive patients.

Association of urinary albumin concentration with casual and ambulatory blood pressure: a similar relationship in normotensive and hypertensive subjects

BACKGROUND

The urinary albumin level has been found to be positively correlated with blood pressure in hypertensive patients. To our knowledge, this relationship has not been evaluated in normotensive subjects and compared with that in hypertensives using casual and ambulatory blood pressure measurements.

METHODS

In this cross-sectional study, a cohort of 234 normotensive and hypertensive participants wore an ambulatory blood pressure monitor for 24 h, standardized casual blood pressure measurements being taken. The urinary albumin concentration was determined by the dipstick Micral Test. The bivariate and multivariate relationship between urinary albumin concentration and demographic and blood pressure measures was investigated using correlational and regression analyses.

RESULTS

The prevalence of microalbuminuria was significantly greater in the hypertensive than normotensive participants. The urinary albumin concentration was positively associated with both casual and ambulatory measures of blood pressure in both the normotensive and hypertensive subsamples, stronger correlations being found for systolic blood pressure. The relationship between systolic blood pressure and urinary albumin concentration was similar in the normotensive and hypertensive subsamples.

CONCLUSIONS

These findings confirm earlier reports of the greater prevalence of microalbuminuria in patients with hypertension than in normotensive participants, as well as those reporting a continuous relationship in hypertensive participants. This study extends prior research to a normotensive subsample, in whom a similar relationship of blood pressure to microalbuminuria, using both ambulatory and casual measures of blood pressure, was found. Future research should investigate the causal direction of this relationship.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Ambulatory blood pressure and urinary albumin excretion in clinically healthy subjects

A slightly elevated urinary albumin excretion rate (UAER) is a predictor of atherosclerotic cardiovascular disease. The mechanism is unknown, but moderate office blood pressure elevation has been demonstrated as part of a clustering of known atherosclerotic risk factors in subjects with elevated UAER. Because 24-hour ambulatory blood pressure is a superior predictor of hypertensive target organ involvement, we aimed to investigate blood pressure profile in clinically healthy subjects with elevated UAER. Ambulatory blood pressure monitoring was performed with a portable recorder in 27 subjects with an elevated UAER (>6.6 microg/min, overnight urine collection) and 46 normoalbuminuric control subjects. Mean+/-SD systolic and diastolic ambulatory blood pressures (24-hour) were significantly higher in subjects with elevated UAER than in normoalbuminuric controls (134+/-12 versus 128+/-11 mm Hg and 78+/-7 versus 75+/-6 mm Hg, P<0.05), as were systolic and diastolic blood pressure loads [median (range): 42% (6 to 94%) versus 23% (1 to 89%) and 20% (0 to 68%) versus 6% (0 to 62%), P<0.05]. The circadian variation of blood pressure was normal in subjects with elevated UAER. However, the increased urinary loss of albumin could not be solely related to the higher blood pressure. In conclusion, apparently healthy subjects with elevated UAER had slightly but significantly higher 24-hour systolic and diastolic blood pressure levels in addition to increased blood pressure loads but normal circadian variation. The demonstrated differences in blood pressure may offer a partial explanation for the association between elevated urinary albumin excretion and atherosclerotic cardiovascular risk.

High altitude-induced albuminuria in normal man is enhanced by infusion of low-dose dopamine

Renal function and the urinary excretion rate of albumin (Ualb) at rest and during infusion of dopamine (3 micrograms kg-1 min-1) were investigated in eight normal volunteers at sea level and 48 h after a rapid, passive ascent to an altitude of 4350 m. Oxygen saturation decreased to 81% (77-85) (median with quartiles in parentheses) at high altitude. High altitude hypoxia increased Ualb from 3.2 micrograms min-1 (2.7-3.5) to 5.0 micrograms min-1 (3.3-6.6) (p < 0.05); increased mean arterial blood pressure from 80 mmHg (73-95) to 102 mmHg (96 108) (p < 0.01); decreased the effective renal plasma flow (ERPF) from 465 ml min-1 (412-503) to 410 ml min-1 (385-451) (p < 0.05), and increased the filtration fraction from 24% (22-27) to 28% (26-29) (p < 0.01). Glomerular filtration rate (GFR), and the renal clearances of lithium (CLi) and sodium (CNa) remained unchanged at high altitude. Dopamine increased ERPF, GFR, CLi, CNa, and decreased the filtration fraction in both environments. Infusion of dopamine further increased Ualb to 10.5 micrograms min-1 (5.5-64.8) (p < 0.05) at high altitude, but had no effect on Ualb at sea level. In conclusion, high altitude hypoxia per se increases the urinary excretion rate of albumin, which is further increased by the renal vasodilating drug dopamine. This effect of dopamine at high altitude may result from combined effects of the increase in renal plasma flow and a hypoxia-induced increase in the glomerular capillary permeability to albumin.

Lisinopril reduces postexercise albuminuria more effectively than atenolol in primary hypertension

Physical exercise causes transient albuminuria. The mechanisms of postexercise albuminuria are not fully clarified but stimulation of the reninangiotensin system (RAS) probably plays a major role through intrarenal haemodynamic changes causing an elevated filtration pressure. In a randomised, double-blind, crossover study we compared the effects on urinary albumin excretion (UAE) of lisinopril (L) and atenolol (A) therapy, i.e. we aimed to investigate whether inhibition of the RAS or inhibition of beta1-adrenoceptor-mediated effects of the sympathetic nervous system differed with regard to changes in UAE. Sixteen patients with uncomplicated primary hypertension were studied. Four standardised bicycle ergometer exercise tests were performed, before and after each active treatment period. UAE 30 min postexercise, determined by radioimmunoassay, was significantly lowered by both treatments: -278 mu g center dot min-1 (L) and -199 mu g center dot min-1 (A). The reduction of postexercise UAE achieved by treatment with the angiotensin-converting enzyme (ACE) inhibitor (L) was significantly greater than that achieved by the beta1-selective adrenoceptor blocker treatment. Blood pressure (BP) at rest and during exercise were equally reduced by both drugs. In conclusion, this study showed that antihypertensive treatment with an ACE inhibitor was more effective in reducing exercise-induced albuminuria than a beta1-selective adrenoceptor-blocking agent with a similar degree of BP reduction in patients with uncomplicated primary hypertension. This suggests that the RAS plays a major role in postexercise albuminuria in hypertensive subjects. The clinical significance of this finding, however, remains to be clarified.

Renal effects of nifedipine and captopril in patients with essential hypertension and reduced renal reserve

In this study we investigated the short-term effects of calcium channel blockers and angiotensin-converting enzyme inhibitors on renal hemodynamics and the urinary excretion of proteins with different relative mass in subjects with mild to moderate essential hypertension and apparently normal glomerular filtration rate but reduced renal functional reserve. Sixteen subjects underwent the following four treatments: (1) low-protein meal (0.2 g protein/kg body wt), (2) high-protein meal (1.3 g protein/kg body wt), (3) high-protein meal plus oral nifedipine (20 mg), and (4) high-protein meal plus oral captopril (50 mg). Two urine samples were obtained after meals. Blood samples were drawn at the midpoint of each 120-minute urine collection period. Urine and serum were tested for total protein, immunoglobulin G, albumin, alpha 1-microglobulin, retinol binding protein, and beta 2-microglobulin. Glomerular filtration rate and renal plasma flow were assessed by iothalamate and p-aminohippuric clearance, respectively. Compared with the high-protein meal alone, nifedipine elicited a clear-cut increase in the urinary excretion of total protein (+60%, P < .01), immunoglobulin G (+58%, P < .01), albumin (+25%, P < .05), retinol binding protein (+47%, P < .05), and beta 2-microglobulin (+52%, P < .05); captopril decreased the urinary excretion rate of immunoglobulin G (-26%, P < .05), albumin (-22%, P < .05), and beta 2-microglobulin (-34%, P < .05). The ratio between the clearances of immunoglobulin G and albumin was higher after nifedipine (+21%, P < .01) and unchanged after captopril (-9%, P = NS) compared with the high-protein meal alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of microalbuminuria in the general population

Microalbuminuria in the general population is associated with recognized risk factors for cardiovascular disease such as hypertension, hyperglycemia, hyperinsulinemia, and hyperlipidemia; and it is an independent predictor of subsequent cardiovascular mortality in hypertensive, diabetic, and elderly populations. Although different methods have been used for measuring and expressing urinary albumin excretion and a variety of cutoff levels have been used for defining microalbuminuria, prevalence of microalbuminuria appears to be higher in non-Europeans (8%-28%) than in Europeans (2%-10%). However, because of the large within-individual variability of urinary albumin excretion and the relatively low prevalence of microalbuminuria, large studies are required to detect statistically significant associations between albuminuria and cardiovascular risk factors. Evidence presented here supports the proposition that microalbuminuria represents a marker of cardiovascular disease risk in nondiabetic individuals as well as diabetic individuals. Moreover, because of a high sensitivity of the test and because albuminuria is a concomitant of many forms of renal disease, microalbuminuria also has a role in detecting patients with renal involvement associated with essential hypertension, lupus erythematosus, women with pre-eclampsia, and subjects with unsuspected primary and secondary nephropathies.

A comparative study of lisinopril and atenolol on low degree urinary albumin excretion, renal function and haemodynamics in uncomplicated, primary hypertension

The presence of slightly increased urinary albumin excretion (UAE), even at levels well below levels detectable by an ordinary dipstick, has been suggested as a predictor of cardiovascular morbidity and as a reflection of the degree of overall vascular permeability. The aim of the present investigation was to study the effects of two different antihypertensive drug regimens, an ACE inhibitor and a beta-adrenoceptor antagonist, on the low UAE rate observed in subjects with uncomplicated, mild to moderate primary hypertension. After a 4-week placebo run-in period, 49 patients (mean age 54 y) were randomly assigned in a double blind manner either to further 4 weeks on placebo (P, n = 15), 8 weeks on lisinopril (L, n = 17; 20 mg/40 mg o.d.) or 8 weeks on atenolol (A, n = 17; 50 mg/100 mg o.d.). The 24-h UAE was measured every second week. At entry and after 4 weeks the glomerular filtration rate and the renal plasma flow were measured. Both drugs lowered blood pressure (BP) to a similar extent after 4 and 8 weeks of treatment; the blood pressures were 160/106 (P), 159/104 (L) and 154/103 (A) at entry, and 133/83 (L) and 134/87 (A) at the end of the study after 8 weeks. On entry the 24-h UAE in all patients ranged from 4 to 49 mg (mean 14.1 mg), and it did not differ significantly between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary albumin excretion in patients with familial Mediterranean fever: a pilot study

Amyloidosis of the kidney is the most threatening complication in familial Mediterranean fever (FMF), and colchicine has been shown to reduce its occurrence. In the preclinical stage of kidney amyloidosis, no proteinuria is observed by the standard Albustix method. However, whether these patients have normal or increased urinary albumin excretion is not known. The purpose of this study was to evaluate albumin excretion in FMF patients treated with colchicine and to compare these values to those of a normal control group. Twenty-two subjects with FMF were compared with 16 normal subjects matched with regard to age and body surface area. The two groups did not differ with regard to female/male ratio and arterial pressure. Urine samples were collected overnight while patients were recumbent and in the daytime while they were ambulant. After measuring albumin concentration (Ua) by radio-immunoassay and creatinine concentration through the standard method, the urinary albumin excretion rate (UaV) and urinary albumin creatinine ratio (Ua/c) were calculated. In the FMF group, three patients had microalbuminuria--defined as an albumin excretion rate higher than 20 micrograms/min. Two of them had this condition only in the early morning collection. These three patients were characterized by a longer duration of symptoms (18 vs. 9 years). No patient in the control group had microalbuminuria. The mean UaV in the FMF group did not differ significantly from that of the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of renal diseases in humans: developing markers and methods

This review covers the tests currently available or being developed for early detection of renal damage and dysfunction induced by exogenous chemicals. Relevant markers are discussed with regard to their application and their level of validation. Some of these tests are being used routinely within health surveillance programmes of individuals exposed to known nephrotoxic agents. More sensitive tests can be applied in epidemiological surveillance programmes aimed at the identification and removal of relevant risk factors. The earliest changes might have little clinical significance, although new perspectives may be opened by various markers and approaches that are being developed.

Microalbuminuria in diabetes: a population study of the prevalence and an assessment of three screening tests

A single observer reviewed 842 of the 917 known diabetic patients registered with 40 GPs in the Poole area. A midstream urine specimen was tested for proteinuria using Albustix (Ames) and cultured to detect bacterial infection. After the first 3 months of the survey, the aliquot of this specimen was frozen for later determination of the random albumin/creatinine ratio (R-Alb/Creat). Patients were requested to submit a timed overnight urine collection for estimation of urinary albumin excretion rate (AER). Of the 842 patients reviewed, 493 (59%) submitted timed overnight urine collections; 43 were excluded because of urinary infection and/or proteinuria. One hundred and thirty-three (30%) of 450 diabetic patients were found to have microalbuminuria, although only 31 (7%) had an AER greater than 30 micrograms/min. Six hundred and seven urine samples were collected for R-Alb/Creat but 68 were excluded because of infection and/or proteinuria; in 10 further samples urinary creatinine was not measured. Two hundred and four (38%) of 532 diabetic patients were found to have an elevated R-Alb/Creat. There was a significant correlation between AER and R-Alb/Creat (r = 0.32, p less than 0.001) but a considerable number of patients showed either a normal AER and high R-Alb/Creat or the reverse. The value of R-Alb/Creat or an overnight urinary albumin concentration, or an overnight urinary albumin/creatinine ratio (ON-Alb/Creat) as screening tests to predict AER greater than 30 micrograms/min was assessed. An ON-Alb/Creat greater than 2.0 mg/mmol was the optimal screening test (sensitivity 96% and specificity 99.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary albumin excretion in healthy adult subjects: reference values and some factors affecting their interpretation

A conventional radioimmunoassay has been used to measure urinary albumin concentration in overnight, recumbent and daytime, ambulant samples from 127 healthy, normotensive volunteers (mean age 33.3 yr SD 12.4; 59 males, 68 females). Reference values were obtained for urine albumin concentration (mg/l), albumin/creatinine ratio (mg/mmol), and albumin excretion rate (microgram/min). The frequency distributions of these variables were positively skewed, but became Gaussian on logarithmic transformation of the data. Albumin excretion was significantly higher in daytime, ambulant samples than in overnight, recumbent samples (p less than 0.001). Surface area was not correlated with urine albumin concentration but it was negatively correlated with urine albumin/creatinine ratio (p less than 0.05) due to the association between surface area and creatinine excretion. Urine albumin concentration was negatively correlated with age, but this was due to a higher urine flow rate in older subjects. There was no significant association with sex or with mean arterial blood pressure in the normal range. Two repeated measurements showed that variability was high and comparable for urine albumin concentration, albumin/creatinine ratio and albumin excretion rate: it was not significantly less in overnight, recumbent than in day-time, ambulant samples.

The origin of proteinuria at high altitude

Urinary protein excretion was measured before and after the intravenous infusion of lysine in 14 normal subjects after 4-6 days' acclimatization at 4846 m. Urinary albumin excretion before lysine was elevated in 11 subjects but alpha 1-microglobulin was detected in only four. After lysine a large increase in albumin excretion occurred in all subjects. Together with the absence of alpha 1-microglobulin before lysine this implies that increased glomerular capillary permeability is the major cause of proteinuria after acclimatization to high altitude. The estimated minimum glomerular fluid albumin concentration was increased two to three fold above the published values in normal controls.

Urinary albumin excretion in school children

Concentrations of albumin were measured by an enzyme linked immunoassay in 24 hour urine collections (divided into day and night-time samples) from 183 boys and 191 girls aged 4 to 16 years. The 24 hour albumin excretion rate and day and night-time albumin excretion rates all increased with age in both girls and boys. Albumin excretion during the day exceeded that at night in both girls and boys. Albumin excretion rates were higher in girls than boys during the day but there was no significant difference at night-time. The urinary albumin creatinine ratio showed no change with age, but was greater in girls than boys during the day and at night, and was also greater during the day than at night in both sexes. Graphs of normal values of albumin excretion rates and albumin creatinine ratios are provided.