FGF-23 is a phosphate-lowering hormone. FGF-23 stands for Fibroblast Growth Factor 23. The hormone is produced by bone cells when phosphate metabolism is disturbed or calcitriolCalcitriol is the active form of vitamin D3. It is synthesised in the kidney from vitamin D. It is independently activated by three factors: increased parathyroid hormone levels, reduced calcium levels or indirectly via reduced phosphate levels. Calcitriol acts on four organs: 1) Bones: It... and/or parathyroid hormoneParathyroid hormone (PTH) is a hormone secreted by the parathyroid glands, which regulates calcium levels in the blood. PTH is secreted in response to low blood calcium levels (hypocalcaemia). An increase in calcium concentration above the normal value inhibits PTH production (negative feedback). PTH stimulates... are elevated in the blood. FGF-23 increases phosphate excretion in the kidneys by reducing the retention of phosphate in the tubular system. Like parathyroid hormone, it also inhibits the phosphate transport systems (NaPi2a & NaPi2c) in the tubular system, which are responsible for the retention of phosphate from the primary urineThe initial urine entering the nephron due to filtration of the blood at renal corpuscles. It is not yet concentrated and does not contain any proteins..... As a result, more phosphate is excreted, which lowers the phosphate level in the blood.
FGF-23 also reduces parathyroid hormone and thus the release of phosphate and calcium from the bone. In addition, FGF-23 inhibits the formation of calcitriol, which lowers the blood calcium level. In later stages of chronic kidney disease in humans, an increased blood level of FGF-23 leads to secondary hyperparathyroidismDurch die bestehende Hypokalzämie (erniedrigter Kalzium-Blutspiegel) bei der chronischen Nierenerkrankung, aber auch bei Leber- oder Darmerkrankungen kann es zu einer unkontrollierten Produktion von Parathormon (PTH) in der Nebenschilddrüse kommen.... (SHPT) via the reduction of calcitriol and thus to excessive bone resorptionThe re-uptake of substances from tissues, in particular bone, into the blood. It should not be confused with absorption, the initial uptake of substances into the body, for instance from food in the intestines, through the lungs and via the skin. Reabsorption, in contrast, occurs... by parathyroid hormone with the resulting mineral & bone disorder (MBD). The inhibitory effect of fibroblast growth factor 23 (FGF-23) on the production and release of parathyroid hormone decreases with increasing chronic kidney disease (CKD) stage. Conversely, FGF-23 has a preventative effect on bone mineralisation.
If kidney performance decreases, the FGF-23 blood level rises progressively. In the late stages of CKD, FGF-23 is therefore exponentially higher than at the beginning. High FGF-23 levels are already prognostically unfavourable in early IRIS stages. The blood concentration of FGF-23 is increased when the phosphate balance becomes unbalanced. This may already be the case in the very early stages of CKD – even if the phosphate blood concentration is still within the normal range at this time due to the phosphate-excreting effect of FGF-23. In human medicine, FGF-23 is considered a marker for the progression of chronic kidney disease and is also associated with increased mortality in chronic kidney disease due to its diverse pathological properties.
By measuring FGF-23 again as part of the kidney profile blood test, it is possible to diagnose a derailment of the phosphate metabolism at a very early stage so that phosphate can then be reduced. If the phosphate level in the blood falls, the FGF-23 blood concentration also falls.
