Microalbuminuria

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Classification according to ICD-10
R80 Isolated proteinuria
albuminuria onA
ICD-10 online (WHO version 2019)

Microalbuminuria is the excretion of excessive amounts of albumin in the urine . In people with diabetes mellitus or high blood pressure , microalbuminuria is found in around 10 to 40% of those affected. The incidence of microalbuminuria in the normal population is around 5 to 7%. The level of albumin excretion is an independent risk factor for the later occurrence of kidney disease , cardiovascular diseases such as heart attack , stroke or circulatory disorders and for increased mortality . Therapies that reduce albumin excretion also reduce the risk of cardiovascular disease. Individual differences in the level of albumin excretion can already be detected shortly after birth and probably reflect individual differences in the function of the endothelial cells , the innermost cell layer of the blood vessels .

definition

Normally, the kidneys of adults excrete 20 to 30 mg albumin per day in the urine ( normalbuminuria ). The excretion of 30 to 300 mg albumin within 24 hours or an album concentration of 20 to 200 mg / l in the urine is called microalbuminuria , the excretion of more than 300 mg albumin within 24 hours as macroalbuminuria or proteinuria . Recently there has been discussion of replacing the term microalbuminuria with "subliminal albumin excretion". The background to this is the misunderstanding of the term, which does not mean a "smaller" albumin molecule, but refers to a small amount of albumin in the urine. Current international nephrological guidelines no longer use the term microalbuminuria.

proof

Microalbuminuria cannot be detected with conventional urine test strips. Conventional urine rapid tests only record an excretion of more than 300 to 500 mg albumin per day. Various antibody- based detection methods are available to detect microalbuminuria : radioimmunoassay , nephelometry , immunoturbidimetry and ELISA . By means of HPLC and albumin can be detected which does not react with antibodies. The gold standard is the determination of albumin in urine, which was collected over 24 hours. By simultaneously determining albumin and creatinine and calculating the albumin-creatinine quotient, the urine need not be collected: microalbuminuria is defined by an albumin / creatinine quotient of 30 to 300 mg / g, macroalbuminuria by an albumin / creatinine quotient > 300 mg / g. For early detection, antibody-based test strips are used for the semi-quantitative detection of low albumin concentrations in the urine.

Pathophysiology

Albumin is a relatively large, negatively charged protein ( molecular weight 69  kDa , size 36  Å ). Before albumin gets into the urine, it has to pass the capillary wall in the kidney corpuscle . The endothelial cells of the kidney corpuscle have a strongly negatively charged glycocalyx on the cell membrane . The pores of the kidney corpuscles form a size and charge-specific filtration barrier and prevent the negatively charged albumin from passing through. 99% of the albumin that still crosses the blood-urinary barrier is recovered ( reabsorbed ) and broken down by the cells in the foremost section of the kidney tubules, the proximal tubular cells . High blood pressure and diabetes increase the pressure in the kidney corpuscle and thus increase the amount of filtered albumin. In addition, excessively high blood sugar (hyperglycaemia) can reduce the negative charge of the glomerular capillary endothelial cells and thus increase the permeability of the blood-urinary barrier for albumin. If the filtered amount of albumin exceeds the capacity of the cells of the proximal tubule for reabsorption, or if this is reduced due to damage to the proximal tubule cells , the albumin excretion in the urine increases, initially leading to microalbuminuria and with further increasing damage to macroalbuminuria or proteinuria.

Epidemiology

Microalbuminuria can be detected in 20 to 40% of diabetics who are not known to have kidney disease ( prevalence ). Every year, 2 to 2.5% of diabetics with normal albumin excretion develop microalbuminuria for the first time ( incidence ). Type 1 diabetics are particularly at risk if they have an increased waistline .

In patients with high blood pressure, microalbuminuria can be detected in around 8 to 23% of those affected. In the normal population, microalbuminuria is found in 5 to 7% of the people examined.

Microalbuminuria as a risk factor

In patients with diabetes mellitus, the occurrence of microalbuminuria marks the transition from the early stage of kidney involvement with an increased glomerular filtration rate (stage of hyperfiltration) to the stage of increasing renal function loss. In people who do not have diabetes mellitus, microalbuminuria indicates an increased risk of developing manifest kidney disease in the next few years .

Compared to diabetics with normal albumin excretion, diabetics with microalbuminuria have an approximately 2.4 times higher risk of dying from cardiovascular complications. Even in people with high blood pressure (hypertensive patients) and in the normal population, if microalbuminuria is detected, the risk of developing cardiovascular disease within the next five years (morbidity) or death (mortality) is increased. In addition, microalbuminuria increases the risk of developing dementia or venous thromboembolism .

Even if the albumin excretion is still in the normal range (albumin / creatinine quotient <25 mg / g), higher values ​​are associated with an increased risk of developing high blood pressure later in life .

Screening

The examination for microalbuminuria is used in diabetics for the early detection of kidney involvement . In patients with hypertension, evidence of microalbuminuria is used to identify those individuals at increased cardiovascular risk who will benefit from more intensive treatment for hypertension.

therapy

ACE inhibitors and AT1 antagonists can prevent the recurrence of microalbuminuria in diabetics and improve microalbuminuria in diabetics and hypertensive patients. A reduction in the excretion of albumin leads to a reduction in the risk of developing cardiovascular diseases.

Guidelines

The guideline of the National Kidney Foundation of the USA recommends that patients with diabetes be examined annually for the presence of diabetic nephropathy, immediately after diagnosis of type 2 diabetes and from the 5th year after diagnosis of type 1 diabetes. If micro- or macroalbuminuria is found in 2 out of 3 urine samples, chronic kidney damage is present. A diabetic nephropathy is most likely present in macroalbuminuria, in microalbuminuria after at least 10 years of type 1 diabetes, or in microalbuminuria and simultaneous diabetic retinal damage (diabetic retinopathy) . Diabetic nephropathy should be treated with an ACE inhibitor or an AT1 antagonist . The blood pressure should be set to values ​​below 130/80 mmHg.

The guidelines for the diagnosis and treatment of arterial hypertension of the German Hypertension League recommend the determination of microalbuminuria in all diabetics and, if possible, also in non-diabetic patients with hypertension. If microalbuminuria is detected, aggressive blood pressure lowering and drug blocking of the renin-angiotensin system are recommended.

literature

Individual evidence

  1. ↑ In adult humans, 20 to 200 mg / l or 30 to 300 mg per day
  2. ↑ G. Herold: Internal Medicine . 2010, p. 577 .
  3. ↑ a b c d D. de Zeeuw: Microalbuminuria as an Early Marker for Cardiovascular Disease . In: J Am Soc Nephrol . No. 17 , 2006, p. 2100-2105 ( asnjournals.org ).
  4. ↑ a b c d M. R. Weir: Microalbuminuria and Cardiovascular Disease . In: Clin J Am Soc Nephrol . No. 2 , 2007, p. 581-590 ( asnjournals.org ).
  5. ↑ Richard Daikeler, idols Use, Sylke Waibel: diabetes. Evidence-based diagnosis and therapy. 10th edition. Kitteltaschenbuch, Sinsheim 2015, ISBN 978-3-00-050903-2 , p. 152 f.
  6. ↑ CKD EVALUATION & MANAGEMENT | KDIGO. (No longer available online.) In: kdigo.org. Archived from the original on July 21, 2016 ; accessed on July 21, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / kdigo.org
  7. ↑ CDA Stehouwer u. a .: Microalbuminuria and Risk for Cardiovascular Disease: Analysis of Potential Mechanisms . In: J Am Soc Nephrol . No. 17 , 2006, p. 2106-2111 ( asnjournals.org ).
  8. ↑ Ian H. de Boer et al. a .: Central Obesity, Incident Microalbuminuria, and Change in Creatinine Clearance in the Epidemiology of Diabetes Interventions and Complications Study . In: J Am Soc Nephrol . No. 18 , 2007, p. 235-243 ( asnjournals.org ).
  9. ↑ AH Brantsma et al. a .: Extended Prognostic Value of Urinary Albumin Excretion for Cardiovascular Events . In: J Am Soc Nephrol. Sep; 19 (9), 2008, pp. 1785-1791 , PMID 18525003 .
  10. ↑ DJ Magliano et al. a .: HPLC-Detected Albuminuria Predicts Mortality . In: J Am Soc Nephrol . No. 18 , 2007, p. 3171-3176 ( asnjournals.org ).
  11. ↑ Scott D. Solomon et al. a .: Influence of Albuminuria on Cardiovascular Risk in Patients With Stable Coronary Artery Disease . In: Circulation . No. 116 , 2007, pp. 2687-2693 ( ahajournals.org ).
  12. ↑ Joshua I Barzilay, Annette L Fitzpatrick, Jose Luchsinger, Sevil Yasar, Charles Bernick, Nancy S Jenny, Lewis H Kuller: Albuminuria and dementia in the elderly: a community study . In: American Journal of Kidney Diseases . tape 52 , no. 2 , August 2008, ISSN  1523-6838 , p. 216-226 , doi : 10.1053 / j.ajkd.2007.12.044 , PMID 18468749 .
  13. ↑ Bakhtawar K Mahmoodi, Ron T Gansevoort, Nic JGM Veeger, Abigail G Matthews, Gerjan Navis, Hans L Hillege, Jan van der Meer: Microalbuminuria and risk of venous thromboembolism . In: JAMA: The Journal of the American Medical Association . tape 301 , no. 17 , May 6, 2009, ISSN  1538-3598 , p. 1790-1797 , doi : 10.1001 / jama.2009.565 , PMID 19417196 .
  14. ↑ JP Forman et al. a .: Higher levels of albuminuria within the normal range predict incident hypertension . In: Journal of the American Society of Nephrology . tape 19 , no. October 10 , 2008, ISSN  1533-3450 , p. 1983–1988 , doi : 10.1681 / ASN.2008010038 , PMID 18579639 .
  15. ↑ PE de Jong et al. a .: Screening, Monitoring, and Treatment of Albuminuria: Public Health Perspectives . In: J Am Soc Nephrol . No. 17 , 2006, p. 2120-2126 ( asnjournals.org ).
  16. ↑ KDOQI Clinical Practice Guidelines and Clinical Practice Recommendations for Diabetes and Chronic Kidney Disease . ( Memento of the original from September 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 5.7 MB) Diabetes and Chronic Kidney Disease. US National Kidney Foundation Guideline; February 2007, 180 pp. (English) @1@ 2Template: Webachiv / IABot / www.kidney.org
  17. ↑ Guidelines for the diagnosis and treatment of arterial hypertension ( Memento of the original from September 28, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) German Hypertension League e. V. DHL - German Hypertension Society. @1@ 2Template: Webachiv / IABot / www.hochdruckliga.de