Low on salt: turning the spotlight on kidney donors

General Studies Paper 2

Context

• There is a great deal of attention paid to the recipient of a organ transplant, and rightly so, but the backbone of live kidney transplantation for transplant surgeons is also to make sure that donors do not face the same problem in the future.

Before the donation

• Before donating the donor is fully evaluated to make sure the person is completely normal. Age-matched kidneys may be ideal but usually 18 to 60 years is accepted. Between 60- 70 years, an exceptional kidney function and health may permit donation. Blood group matching is usually required but O can donate to any group.
• Minor ailments may not be a contraindication for donating. Diabetes or pre diabetes, obesity, hypertension, kidney stones, etc. require special attention. Medical evaluation is always biased in the donor’s favour. Diabetes in the donor is usually an absolute contraindication. Hypertension with easy control with a single tablet is permitted.
• It is also essential that the kidney function on special test is at least 75 ml per minute There should no protein leak. Metabolic workup in persons having small stone is a must. Those with multiple stones should be rejected. Normally the evaluation should favour the donor and the better working kidney should be left behind with the donor.

After the donation

• After the donation the person requires life long follow-up. Immediately after the surgery the kidney function drops by almost half and the single kidney starts working more to compensate for the loss of the other. This is a process of hyperfiltration at the microscopic level and compensatory hypertrophy at the gross level.
• Donors require to periodically monitor blood pressure. Kidney function and protein loss should be checked at least once a year. Almost one third of donors would develop hypertension over several years but this almost the same incidence as in the general population. A small percentage would develop protein leak in the urine.
• It is essential that the donors are instructed properly with regards to diet, exercise and avoidance of drugs toxic to the kidneys. DASH diet (dietary approaches to stop hypertension) would be ideal. Sufficient vegetables, fruits, whole grains, lean meat, moderate restriction of salt and sugar, and avoidance of transfats is essential.

Salt and Kidney

• The WHO and other medical associations caution on the importance of salt restriction to 5 gms per day in the general population. The 5 gms includes salt present in natural food, salt added during cooking and hidden salt present in preserved or packed food like bread and noodles. Restriction of salt reduces not only blood pressure but also strokes and kidney failure.

Calculating kidney function

• Creatinine is produced by muscles in the body and excreted by the the kidneys. Since normally only kidneys remove the creatinine ,its measurement in blood reflects kidney function .
• Mathematical formulae adjusting for age, weight and sex are used to calculate kidney function and express as eGFR(Glomerular function rate).
• Protenuria or protein leak is a more sensitive test and 85% of the kidney diseases are detected earlier than creatinine estimation. Protein has a large molecular weight and does not appear in the urine unless the microscopic vessel (glomerulus)in the kidney is damaged or it is secreted by tubules.
• The quantity of protein loss in the urine reflects the kidney damage and is used as a measure to see the response for treatment.
• Proteinurea unlike creatinine is not only a marker of kidney disease but also a cause for progression of kidney disease.
• This understanding has led to the development of several group of drugs which would lower protein loss to reduce damage to the kidneys. They include the anti renin system (ACE and ARB) group of drugs, the SGLT2 inhibitors, anti aldosterone drugs etc.

Conclusion

• A recent study from MIOT international on the salt intake in renal donors has highlighted the importance of monitoring salt intake in kidney donors Chronic Kidney disease(CKD) affects almost 10% of the worlds population. So it is essential to detect CKD early and intervene to halt the disease.  It is hightime we realise the importance of this, and implement salt reduction globally.