The authors have declared that no competing interests exist.
Conceived and designed the experiments: TT TK MM RI KF YI. Performed the experiments: TT TK KO SR. Analyzed the data: TT TK YI. Contributed reagents/materials/analysis tools: TT TK TO HI YI. Wrote the paper: TT YI.
It is thought that a large amount of albumin leaking from the glomerulus in nephrotic syndrome (NS) is reabsorbed at the proximal tubule and catabolized. Therefore, it is possible the final quantity of urinary protein does not always reflect the amount of leakage of protein from the glomerulus. We experienced two cases without nephrotic range proteinuria thought to involve hypoproteinemia due to the same pathophysiology as NS. On these patients, we performed protein leakage scintigraphy with technetium-99m human serum albumin diethylenetriamine pentaacetic acid (99mTc-HSAD) to exclude a diagnosis of protein-losing gastroenteropathy and observed diffuse positive accumulation in the kidneys with more intense uptake in the kidney than the liver on the anterior view 24 hours after 99mTc-HSAD administration. In healthy adults intravenously given 99mTc-HSAD, the same dynamics are observed as in albumin metabolism, and the organ radioactivity of the liver and kidneys after 24 hours is equal. Therefore, we thought it was possible that the renal uptake 24 hours after 99mTc-HSAD administration was a characteristic finding of NS. In order to confirm it, the subjects were divided into two groups: the NS group (n = 10) and the non-NS group (n = 7). We defined more intense uptake in the kidney than the liver on the anterior view 24 hours after 99mTc-HSAD administration as Dense Kidney (+). Furthermore, we designed regions of interest in the right and left kidneys and liver on anterior and posterior images, then calculated the kidney-liver ratio. Nine of the ten patients had Dense Kidney (+) in the NS group, compared to none in the non-NS group. And the kidney-liver ratio was significantly higher in the NS group than in the non-NS group on each view in the bilateral kidneys. In conclusion, our results suggest that the renal uptake 24 hours after 99mTc-HSAD administration is a characteristic finding of NS.
Many illness, including disturbances of protein synthesis (liver disease), inflammatory diseases and protein leakage from the gastrointestinal tract, can cause hypoproteinemia. Nephrotic syndrome (NS) is also a common cause, and the onset of hypoproteinemia is closely related to proteinuria, usually being diagnosed when the proteinuria is severe (generally more than 3.5 g/day). However, it has long been suggested that the degree of hypoproteinemia may not always depend on the severity of proteinuria alone [
We previously reported two patients with minor glomerular abnormalities who did not exhibit a large enough quantity of urine protein to cause NS, although their hypoproteinemia responded to steroids [
We generally perform protein leakage scintigraphy with 99mTc-HSAD to diagnose protein-losing gastroenteropathy. If there is the exudation of 99mTc-HSAD from the gastrointestinal tract and the tracer visually accumulates in its region, protein leakage scintigraphy is considered positive.
In healthy adults intravenously given 99mTc-HSAD for protein leakage scintigraphy, the material accumulates in bloodstream-rich organs (heart, liver, lungs, etc.), including the kidneys, according to the same dynamics as albumin metabolism, then continues to circulate through the blood vessels for a long period [
Reproduced from Tamaki N et al. [
Therefore, the renal uptake 24 hours after 99mTc-HSAD administration may suggest hyperfunction of urine protein reabsorption due to massive leakage from the glomeruli, which may be utilized to diagnose a nephrotic state. To the best of our knowledge, no similar studies have been reported to date. The objective of this study was to assess the efficacy of the renal uptake observed 24 hours after 99mTc-HSAD administration to discriminate between NS and non-NS.
This study was approved by the Human Research Ethics Committee of Saga University (Permit Number: 2013-07-10). The clinical data collected and analyzed in this study were obtained not for research purposes, but rather to provide appropriate medical care, and analyzed anonymously. This study was conducted according to the principles expressed in the Declaration of Helsinki.
We performed a single-center, retrospective study of Japanese patients using medical records at the Saga University Faculty of Medicine, Saga, Japan. The study population included patients who were considered to need a differential diagnosis of protein leakage from the gastrointestinal tract, and who underwent protein leakage scintigraphy with 99mTc-HSAD at our hospital between January 1, 2008 and March 31, 2014. A total of 33 patients received protein leakage scintigraphy with 99mTc-HSAD. Subjects were excluded if they had no definitive diagnosis or urinary data. We defined the NS group (10 patients) as subjects with a urine protein-creatinine ratio (U-Pro/Cr) above 3.5 g/g and the non-NS group (seven patients) as those with a U-Pro/Cr below 0.3 g/g or equal findings from a qualitative analysis of urine (
72 | F | 21.7 | 3+ | 6.06 | 5.1 | 2.2 | 270 | 191 | 159 | 0.58 | membranous nephropathy | |
33 | F | 20.2 | 4+ | 4.16 | 5.2 | 1.8 | 241 | 149 | 68 | 0.57 | minimal change | |
53 | F | 23.2 | 3+ | 3.60 | 5.2 | 2.7 | 228 | 145 | 88 | 0.86 | minimal change | |
76 | F | 18.4 | 4+ | 5.98 | 5.0 | 2.2 | 204 | 136 | 133 | 1.29 | focal segmental glomerulosclerosis | |
58 | M | 31.1 | 4+ | 5.43 | 3.4 | 1.0 | 383 | 279 | 190 | 1.68 | focal segmental glomerulosclerosis | |
75 | F | 21.1 | 4+ | 11.90 | 5.4 | 2.0 | 295 | 158 | 197 | 0.55 | minimal change | |
24 | F | 20.5 | 4+ | 4.51 | 4.3 | 0.9 | 433 | 279 | 171 | 0.66 | minimal change | |
57 | F | 21.9 | 4+ | 7.78 | 3.8 | 0.6 | 541 | 434 | 236 | 0.91 | minimal change | |
70 | F | 18.4 | 4+ | 6.12 | 3.9 | 1.4 | 377 | 281 | 261 | 0.53 | membranous nephropathy | |
70 | F | 21.8 | 4+ | 6.47 | 5.7 | 2.0 | 192 | 116 | 165 | 0.49 | membranous nephropathy | |
58.8 ± 17.9 | 21.8 ± 3.6 | 6.20 ± 2.34 | 4.70 ± 0.78 | 1.68 ± 0.68 | 316.4 ± 113.7 | 216.8 ± 99.8 | 166.8 ± 59.9 | 0.81 ± 0.39 | ||||
79 | F | 27.7 | (-) | ND | 4.5 | 1.2 | 101 | 36 | 47 | 1.08 | malabsorption syndrome, chronic pancreatitis | |
70 | M | 17.0 | (±) | 0.18 | 5.7 | 2.4 | 143 | 89 | 107 | 0.83 | malabsorption syndrome, chronic pancreatitis | |
53 | F | 19.3 | (-) | 0.15 | 3.9 | 1.4 | 120 | 51 | 195 | 0.97 | Crohn's disease, protein-losing gastroenteropathy | |
59 | M | 18.7 | (-) | ND | 3.7 | 1.5 | 111 | ND | 152 | 0.53 | eosinophilic gastroenteritis, protein-losing gastroenteropathy | |
58 | M | 21.4 | (-) | ND | 6.4 | 3.4 | 197 | 117 | 171 | 0.59 | Cronkhite-Canada syndrome | |
14 | F | 22.5 | (-) | ND | 6.2 | 3.1 | 258 | ND | 229 | 0.54 | Lupus entelitis | |
72 | M | 17.7 | (-) | ND | 5.3 | 2.6 | 122 | ND | 80 | 0.60 | blind loop syndrome | |
57.9 ± 21.4 | 20.6 ± 3.7 | 0.17 ± 0.02 |
5.10 ± 1.08 | 2.23 ± 0.87 | 150.3 ± 57.0 |
73.3 ± 36.7 |
140.1 ± 65.0 | 0.73 ± 0.22 |
*P < 0.05 vs. NS group,
+P < 0.01 vs. NS group.
Proteinuria; (-): ~9 mg/dl, (±): 10~29 mg/dl, (1+): 30~99 mg/dl, (2+): 100~299 mg/dl, (3+): 300~999 mg/dl, (4+): 1000 mg/dl~
Abbreviations. NS: nephrotic syndrome, M: male, F: female, BMI: body mass index, U-pro/cr: urinary protein-creatinine ratio, TP: serum total protein, Alb: serum albumin, T-cho: serum total cholesterol,
LDL-C: serum low-density lipoprotein cholesterol, TG: serum triglycerides, Cr: serum creatinine, ND: no data.
All patients received a single intravenous dose of 740 MBq of 99mTc-HSAD (Poolscinti, Nihon Medi-Physics, Tokyo, Japan), and static images (both anterior and posterior images) were obtained 24 hours after the administration of the radiopharmaceutical with the patient being kept in the supine position for eight minutes. The radiochemical purity level of 99mTc-HSAD was higher than 90% [
Scintigraphy was performed using a digital gamma camera (Symbia E, Siemens Japan K.K., Tokyo, Japan) with a rectangular field detector attached to a low-energy, high-resolution collimator. A 15% energy window centered over 140 keV (99mTc photopeak) with a matrix of 512 ×512 and magnification of 1.45x was used. We processed the images and analyzed the results using the Syngo MI Workplace (Siemens Japan K.K., Tokyo, Japan).
In the qualitative analysis, we defined the presence of a more intense uptake in the kidney than the liver on the anterior view 24 hours after 99mTc-HSAD administration as Dense Kidney (+) (
We defined the presence of a more intense uptake in the kidney (
Regions of interest in the right and left kidney and liver were designed on anterior and posterior images, respectively, in order to obtain the count per region 24 hours after 99mTc-HSAD administration. The semi-quantitative analysis was performed by dividing the count per region in the right and left kidney by the count per region in the liver (kidney-liver ratio: K/L) and comparing the results between the two groups.
All biochemical assays were performed at the laboratory of Saga University Hospital, which complied with the International Federation of Clinical Chemistry and Laboratory Medicine. The urinary protein from spot urine samples was measured using the pyrogallol red method, and the urinary creatinine from spot urine was measured using an enzymatic method. Serological tests were done by the following methods: the total protein was determined by the Biuret reaction, albumin by the modified BCP assay, and the total cholesterol, low-density lipoprotein cholesterol, triglycerides and creatinine levels were determined by enzymatic methods. The time interval between the biochemical tests and imaging studies in all cases was less than 14 days.
The statistical significance of differences between the groups was determined using Student's t-test or the Mann-Whitney U test. A two-sided P-value was considered to be significant for P values of < 0.05. The data are expressed as the mean ± SD, and K/L is also presented as geometric mean ± geometric SD in parentheses. All analyses were performed using the SPSS 22.0 (IBM Japan, Tokyo, Japan).
The U-Pro/Cr (6.20 ± 2.34: 0.17 ± 0.02, P < 0.05) and serum total cholesterol (316.4 ± 113.7: 150.3 ± 57.0 mg/dL, P < 0.01) and serum low-density lipoprotein cholesterol (216.8 ± 99.8: 73.3 ± 36.7 mg/dL, P < 0.05) levels were significantly higher in the NS group than in the non-NS group, reflecting the clinical differences in pathophysiology between the two groups. There were no significant differences between the groups in the other parameters.
In the NS group, nine of the ten patients (90%) had Dense Kidney (+), one patient (10%) had Dense Kidney (±) and no patients had Dense Kidney (-). In the non-NS group, no patients had Dense Kidney (+), five of the seven patients (71%) had Dense Kidney (±) and two patients (29%) had Dense Kidney (-), with significant differences between the groups (P < 0.001).
NS group (n = 10) | Dense Kidney | non-NS group (n = 7) | Dense Kidney |
---|---|---|---|
(+) | (-) | ||
(+) | (±) | ||
(+) | (-) | ||
(+) | (±) | ||
(±) | (±) | ||
(+) | (±) | ||
(+) | (±) | ||
(+) | |||
(+) | |||
(+) | |||
n = 9 (90%) | n = 0 (0%) | ||
n = 1 (10%) | n = 5 (71%) | ||
n = 0 (0%) | n = 2 (29%) |
Abbreviations. NS: nephrotic syndrome.
The visual analysis clearly showed that the renal uptake of 99mTc-HSAD was remarkably more intense in the NS group than in the non-NS group.
The semi-quantitative analysis confirmed the results of Method 1.
The liver is located ventral to the kidney anatomically; therefore, the K/L was lower on the anterior view than on the posterior view 24 hours after 99mTc-HSAD administration.
On the anterior view, the K/L in the right kidney was 1.26 ± 0.28 (1.24 ± 1.24) in the NS group and 0.75 ± 0.16 (0.73 ± 1.27) in the non-NS group, while that in the left kidney was 1.26 ± 0.32 (1.22 ± 1.28) in the NS group and 0.71 ± 0.21 (0.69 ± 1.35) in the non-NS group (
A: right kidney, B: left kidney.
On the posterior view, the K/L in the right kidney was 2.02 ± 0.48 (1.98 ± 1.25) in the NS group and 1.20 ± 0.31 (1.17 ± 1.27) in the non-NS group, while that in the left kidney was 2.06 ± 0.49 (2.01 ± 1.27) in the NS group and 1.11 ± 0.21 (1.09 ± 1.22) in the non-NS group (
A: right kidney, B: left kidney.
NS is a pathophysiological condition in which a large quantity of proteinuria (more than 3.5 g/day) results in hypoproteinemia. However, the mechanism of hypoproteinemia in NS is unclear [
Analyses of primitive urine gathered according to the micropuncture method have shown that only a very small amount of albumin leaks through the glomerulus in healthy individuals [
Hepatic albumin synthesis increases in response to albumin loss. This effect is mediated by an increase in the hepatic albumin gene expression stimulated in part by a physical factor, low oncotic pressure, which is regulated by the direct effects of low oncotic pressure in hepatocytes [
Furthermore, in NS, protein leakage due to gastrointestinal and stromal edema resulting from capillary hyperpermeability is considered to be a causative factor of hypoproteinemia [
99mTc-HSAD is human serum albumin (HSA) labelled by 99mTc via diethylenetriamine pentaacetic acid (DTPA) due to its strong affinity for 99mTc. Therefore, it has higher label and blood retention rates, superior stability
As mentioned above, when healthy adults are intravenously given 99mTc-HSAD for protein leakage scintigraphy, the same dynamics are observed as in albumin metabolism, and a previous study showed that the organ radioactivity (%ID) of the liver and kidneys after 24 hours is equal, at approximately 10% in humans and 7% in rats [
It is also possible that the above-mentioned two previously reported cases were in the pre-stage of NS and a prolonged stage of healing, respectively. However, nephrologists occasionally encounter patients without nephrotic range proteinuria who exhibit hypoproteinemia in whom the cause of hypoproteinemia is thought to be similar to the pathophysiology of NS. Because NS induces systemic edema, susceptibility to infection due to decreased immunoglobulin production and thrombogenesis resulting from hypercoagulability, early diagnosis and proper treatment are necessary. However, steroid and immunosuppressive therapy carry risks of side effects. Therefore, treatment based on an easy diagnosis is also dangerous.
In conclusion, our results suggest that, in patients who do not exhibit a large enough quantity of urine protein to cause NS and scintigraphy indicates Dense Kidney, the pathophysiology involves hyperfunction of urine protein reabsorption at the proximal tubule with massive leakage from the glomeruli (i.e., a similar pathophysiology to NS). Such findings also aid in the diagnosis of cases in which it is difficult to perform a renal biopsy. We believe that the detection of Dense Kidney using the method described in this study will therefore be a useful diagnostic modality for diagnosing nephrotic syndrome. In the same manner, positive renal scan using gallium-67 citrate scintigraphy has now become a widely accepted examination for diagnosing acute tubulointerstitial nephritis [
Because the evaluation in Method 1 lacked objectivity, we measured the relative contrast ratio of the kidney to the liver in Method 2 and were able to identify significant differences more objectively. However, when used as a supporting examination, Method 1 is a simple and easy tool that is clinically available. Therefore, it is necessary to accumulate more cases including repeating studies during remission of NS in order to assess the usefulness of this method for diagnosis. However, we should be more cautious in the indication for this type of studies and reserve for specific situations of unexplained hypoalbuminemia because the patient may receive a radiation dose of approximately 6mSv by this examination.
The present results suggest that the detection of Dense Kidney 24 hours after 99mTc-HSAD administration for protein leakage scintigraphy reflects the pathophysiology of hyperfunction of urine protein reabsorption at the proximal tubule with massive leakage from the glomeruli. This diagnostic modality is therefore expected to be an effective examination for diagnosing patients without nephrotic range proteinuria which has a pathophysiology similar to that of NS.
We would like to thank our radiation technologist, Mr. Akihiro Narisue for his valuable support in calculating the K/L.