Parathyroid hormone is a peptide hormone secreted by the parathyroid glands, which are located adjacent to the thyroid gland. Parathyroid hormone alters serum calcium via actions on three target organs: bone, intestinal mucosa, and kidney.

Periostin is a secreted extracellular matrix protein that functions in tissue development and regeneration, including wound healing, and ventricular remodeling following myocardial infarction. It binds to integrins to support adhesion and migration of epithelial cells. Periostin is involved in multiple steps of bone metabolism such as osteoblast differentiation, proliferation and adhesion; mediates bone repair and mechanical responses; and regulates bone remodelling and bone strength.

Plasma free metanephrines are commonly used for diagnosis of pheochromocytoma and paraganglioma (PPGLs).

Plasminogen activator inhibitor-1 (PAI-1) is the main physiological inhibitor of plasminogen activators (PAs) and is therefore an important inhibitor of the plasminogen/plasmin system. Being the fast-acting inhibitor of tissue-type PA (tPA), PAI-1 primarily attenuates fibrinolysis. Through inhibition of urokinase-type PA (uPA) and interaction with biological ligands such as vitronectin and cell-surface receptors, the function of PAI-1 extends to pericellular proteolysis, tissue remodeling and other processes including cell migration.

Procollagen type III is found abundantly in skeletal muscle and other soft tissues such as skin, and in negligible amounts in bone. Increased levels of P3NP have been observed during the normal increases in lean mass associated with puberty in adolescent boys and girls, as well as in response to endurance-type exercise in adult males.

Hyperphosphorylation of tau proteins is a characteristic pathological change in AD. There are many sites on the tau protein that may be phosphorylated at various disease stages from preclinical AD to mild cognitive impairment due to AD (MCI-AD) to clinical AD. P-tau181 has been extensively studied and has seen clinical applications such as the use of CSF p-tau181 in the prediction of cognitive decline in patients with MCI.

Hyperphosphorylation of tau proteins is a characteristic pathological change in AD. There are many sites on the tau protein that may be phosphorylated at various disease stages from preclinical AD to mild cognitive impairment due to AD (MCI-AD) to clinical AD. P-tau217 accumulation may differentiate AD from related diseases. The spread of p-tau217 in postmortem brain tissue has shown a correlation with antemortem plasma p-tau217 in those with amyloid plaques but not in those without, suggesting that plasma p-tau217 may reflect the presence of Aβ plaques.

QuantiFERON-TB Gold Plus (QFT-Plus) is an important test that has emerged in recent years for detecting TB infection.

Renin is an aspartyl protease released by the juxtaglomerular cells of the kidneys in response to perceived low blood pressure and renal perfusion. It plays an essential role in the rate-limiting step of the renin-angiotensin-aldosterone system (RAAS), responsible for the homeostasis of blood volume and mean arterial blood pressure.