Kidney Function, Protein Loss and Anaemia
A 64-year-old man attends a clinic with swollen ankles, tiredness and breathlessness. His blood pressure is 158/94 mmHg. Blood tests show creatinine 220 µmol/dm3 (reference 60–110), urea 14 mmol/dm3 (reference 2.5–7.1) and haemoglobin 98 g/dm3 (reference 130–175). Urine testing shows protein 2+ and no glucose. He has no history of diabetes. A 24-hour urine collection contains 1.4 g protein; normal is less than 0.15 g. His eGFR is 32 cm3/min/1.73 m2; above 90 is normal. He takes ibuprofen regularly for knee pain. The doctor explains that his kidneys are not filtering efficiently and advises stopping ibuprofen, reducing salt, and starting a medicine that lowers blood pressure and protects the kidneys. The man asks why he is anaemic and why protein appears in his urine when his diet contains enough protein.
1. Using the data, explain why the man's kidneys are failing to maintain blood composition. Refer to filtration and reabsorption.
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Creatinine and urea are waste products normally removed by the kidneys. Both are above the reference ranges (creatinine 220 vs 60–110; urea 14 vs 2.5–7.1), and eGFR is only 32, so the glomeruli are filtering blood plasma more slowly. Protein in the urine supports damage to the glomerular filter: normally large plasma proteins are held back, but if the filtration barrier is damaged they can pass into the filtrate. The 24-hour protein loss of 1.4 g is far above normal (<0.15 g). Glucose is absent because glucose is normally reabsorbed completely in the proximal tubule and he is not diabetic. Reduced filtration also tends to cause salt and water retention, contributing to his swollen ankles and high blood pressure. The overall picture is reduced kidney function, not simply a diet problem.
2. Explain why the man is anaemic and why stopping ibuprofen is important.
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The kidneys produce erythropoietin (EPO), which stimulates red blood cell production in bone marrow. Scarred, poorly functioning kidneys produce less EPO, so fewer red cells are made and haemoglobin falls to 98 g/dm3, causing tiredness and breathlessness. This is anaemia of chronic kidney disease, not necessarily low dietary protein. Ibuprofen is an NSAID: it reduces prostaglandin production, and prostaglandins help maintain blood flow to the kidney. In someone whose filtration is already reduced, ibuprofen can further reduce renal blood flow and worsen kidney damage, so stopping it is important. The doctor should also check for other causes of anaemia, such as iron deficiency.
3. The doctor says the medicine lowers blood pressure and protects the kidneys. Suggest how high blood pressure can damage kidneys and how lowering it helps.
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Persistently high blood pressure puts extra pressure on the glomerular capillaries. This can damage the delicate endothelium and filtration barrier, allowing more protein to leak and leading to scarring of nephrons, which further reduces filtration. A vicious cycle can develop: kidney damage raises blood pressure, and high blood pressure worsens kidney damage. Lowering blood pressure reduces this mechanical stress. Some blood-pressure medicines, such as ACE inhibitors, also widen the efferent arteriole and lower pressure inside the glomerulus, reducing protein loss and slowing progression. Reducing salt helps lower blood pressure and oedema. The medicine is therefore protecting the kidneys as well as treating the blood pressure.