Kidney health

Creatinine and urea are waste the kidneys clear out of the blood, and eGFR estimates how fast that filtering is going. Sodium, potassium, calcium, magnesium and phosphate are the salts and minerals the kidneys hold in place. Sodium sets how much water the body holds. Potassium and calcium let nerve and muscle cells fire and contract. Magnesium is needed by the enzyme reactions that produce energy, and phosphate is the mineral bone is built from.

Waste builds up in the blood when filtering falls. Filtering can fall a long way before a person feels anything, so a blood test is usually the first sign. The salts matter for a different reason: nerve and muscle cells, the heart among them, need them to work, and the kidneys are what keep them steady.