Parathyroid hormone (PTH) is a peptide hormone secreted by the parathyroid glands, which plays a pivotal role in maintaining calcium and phosphate homeostasis in the body. Consequently, PTH regulation is crucial for bone health and overall metabolic processes. This article aims to provide an in-depth understanding of PTH lab tests, their indications, and their clinical applications.
PTH Lab Test: Description and Reference Range
The PTH lab test quantifies PTH levels in serum or plasma samples. This assessment is instrumental in the evaluation and management of thyroid and kidney disorders, especially in patients with chronic renal failure (CRF). The reference range for PTH levels is dependent on the patient's age and the sample type (serum or plasma).
- Adults (serum):
- C-terminal : 50-330 pg/mL (50-330 ng/L)
- N-terminal: 8-24 pg/mL (8-24 ng/L)
- Intact molecule: 10-65 pg/mL (10-65 ng/L)
- C-terminal (ages 1-16): 51-217 pg/mL (51-217 ng/L)
- N-terminal (ages 2-13): 14-21 pg/mL (14-21 ng/L)
- Intact molecule (ages 2-20): 9-52 pg/mL (9-52 ng/L)
Structure of the PTH molecule
Parathyroid hormone (PTH) is a peptide hormone comprising 84 amino acids, and it plays a significant role in regulating calcium and phosphate levels in the body. The PTH molecule can be divided into three main regions: the N-terminal, C-terminal, and the intact molecule.
The N-terminal region consists of the first 34 amino acids at the PTH molecule's amino (NH2) end. This portion is biologically active and responsible for the majority of PTH's physiological effects, such as stimulating bone resorption, increasing renal calcium reabsorption, and promoting renal phosphate excretion. Furthermore, the N-terminal fragment can be measured using specific immunoassays, helping assess PTH's functionality in various clinical settings.
The C-terminal region refers to the remaining 50 amino acids at the carboxyl (COOH) end of the PTH molecule. This portion is considered biologically inactive, meaning it does not contribute to PTH's physiological actions. However, the C-terminal fragment circulates in the bloodstream and can be measured using immunoassays. Elevated levels of the C-terminal fragment may indicate increased PTH secretion or impaired PTH metabolism.
The intact PTH molecule consists of the entire 84-amino acid peptide hormone, including both the N-terminal and C-terminal regions. Intact PTH is biologically active and can be measured using specific immunoassays that recognize the whole molecule. Intact PTH measurements are often preferred in clinical practice because they provide a more accurate representation of the hormone's activity in the body.
Methods of Assessing PTH levels
Current technologies for assessing parathyroid hormone (PTH) levels predominantly involve immunoassay techniques. Immunoassays are biochemical tests that leverage the specific binding properties of antibodies to target molecules, in this case, PTH. These tests offer high sensitivity and specificity for detecting and quantifying PTH levels in blood samples. The following are the most common immunoassay techniques employed for PTH assessment:
Radioimmunoassay (RIA): RIA is a classic immunoassay technique that uses radioactively labeled PTH molecules as tracers. The assay measures the amount of radioactive PTH bound to its specific antibody. By comparing the binding to a standard curve, the concentration of PTH in the sample can be determined. Although sensitive and specific, RIA has declined in popularity due to concerns over radioactive waste and the availability of alternative techniques.
Enzyme-Linked Immunosorbent Assay (ELISA): ELISA is a widely used immunoassay technique that employs enzyme-linked antibodies to detect PTH. In this assay, a color change occurs when an enzyme substrate is added, and the intensity of this color change is directly proportional to the amount of PTH present in the sample. ELISAs are relatively quick, sensitive, and easy to perform, making them a popular choice for PTH assessment.
Electrochemiluminescence Immunoassay (ECLIA): ECLIA is an advanced immunoassay technique that uses electrochemiluminescence, the production of light resulting from an electrochemical reaction, as a detection method. In ECLIA, the PTH molecules are labeled with a chemiluminescent compound, which emits light upon encountering an electrical current. The intensity of the emitted light is proportional to the amount of PTH present in the sample. ECLIA offers high sensitivity, specificity, and a broad dynamic range.
Chemiluminescent Immunoassay (CLIA): CLIA is another advanced immunoassay technique that utilizes chemiluminescence for detection. In CLIA, the PTH molecules are tagged with a chemiluminescent compound that emits light upon reaction with a specific substrate. The emitted light intensity is measured and is proportional to the PTH concentration in the sample. CLIAs are highly sensitive, specific, and rapid, making them a popular choice in many clinical laboratories.
These immunoassay techniques have revolutionized PTH assessment and contributed to improved diagnosis and management of various endocrine and metabolic disorders. Continuous advancements in assay technology promise further enhancements in PTH detection sensitivity, specificity, and overall efficiency.
Indications and Clinical Applications
Several clinical situations warrant PTH lab test utilization:
- Parathyroidectomy in patients presenting primary hyperparathyroidism.
- Hypocalcemia as a secondary outcome of thyroidectomy.
- Suspected hypercalcemia attributable to hyperparathyroidism.
- Chronic kidney disease.
- Suspected or confirmed bone disease.
Additional tests which may be ordered alongside the PTH lab test:
- Parathyroid panel.
- Direct measurement of serum calcium levels.
- Direct measurement of serum inorganic phosphate levels.
- Test Procedure and Patient Preparation
The PTH lab test generally necessitates a fasting blood sample procured in the morning (8 AM). The patient should abstain from food overnight, consuming only water. It is essential for healthcare practitioners to be apprised of any medications the patient is currently taking, as particular drugs can influence PTH levels.
Sample Storage and Handling
PTH samples must adhere to laboratory guidelines regarding storage and handling, which typically involve immediate freezing and storage at designated temperatures. The sample may require transfer on dry ice to a central laboratory for analysis.
What To Tell the Patient Before and After the Test
Prior to the test, healthcare practitioners should discuss the reason for the PTH test and also inform the patient about fasting requirements. This is important since meal intake can cause spurious elevations in serum PTH.
The PTH lab test is critical in the evaluation and management of various thyroid and kidney disorders. A comprehensive understanding of this test's indications, procedures, and clinical applications allows healthcare providers to ensure accurate diagnosis and optimal patient care.
LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests. First ed. Montvale, NJ: Thomson PDR; 2007.
PTH (Parathyroid hormone) ni homoni ya peptidi iliyotengenezwa na tezi za parathyroid, ambayo ina jukumu muhimu katika kudumisha homeostasis ya kalsiamu na phosphate katika mwili. Kwa hiyo, udhibiti wa PTH ni muhimu kwa afya ya mifupa na michakato ya jumla ya kimetaboliki. Makala hii inakusudia kutoa uelewa wa kina wa vipimo vya maabara ya PTH, dalili zao, na matumizi yao ya kliniki. PTH Lab: Ufafanuzi na Reference Range: PTH Lab ni mtihani wa kiwango cha PTH katika sampuli za seramu au plasma. Utafiti huu ni muhimu katika tathmini na usimamizi wa magonjwa ya tezi na figo, hasa katika wagonjwa wenye upungufu wa figo sugu (CRF). Kiwango cha PTH kinategemea umri wa mgonjwa na aina ya sampuli (seramu au plasma). C-terminal: 50-330 pg mL (0-30 ngL) - N-terminal: 8-24 pg mL (0-65) - Intacte: 10-25 pg mL (0-65) - C-terminal: 1-16 pg mL (1-217) - N-terminal: 14-21 pg mL (1-215) - Intacte: 2-25 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 8-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL (1-215) - Intacte: 9-20 pg mL - Intacte: 9-20 pgL - Intacte PTH inaweza kugawanywa katika sehemu tatu kuu: N-terminal, C-terminal, na molekuli intact. N-terminal ni sehemu ya amino asidi 34 za kwanza kwenye mwisho wa amino (NH2) wa molekuli ya PTH. Sehemu hii ni hai hai na kuwajibika kwa wengi wa athari za kisaikolojia ya PTH, kama vile kuchochea mfupa resorption, kuongeza figo calcium reabsorption, na kukuza figo phosphate excretion. Kwa kuongezea, kipande cha N-terminal kinaweza kupimwa kwa kutumia immunoassays maalum, kusaidia kutathmini utendaji wa PTH katika mazingira mbalimbali ya kliniki. C-terminal ni sehemu ya amino asidi 50 zilizobaki kwenye mwisho wa carboxyl (COOH) ya molekuli ya PTH. Sehemu hii ni inactive, na haina jukumu katika utendaji wa PTH. Hata hivyo, sehemu ya C- terminal inazunguka katika mtiririko wa damu na inaweza kupimwa kwa kutumia immunoassays. Viwango vya juu vya sehemu ya C- terminal vinaweza kuonyesha kuongezeka kwa uvujaji wa PTH au kupungua kwa kimetaboliki ya PTH. PTH ni molekuli ya peptide ya asidi ya amino 84 ambayo ina sehemu ya N-terminal na C-terminal. PTH intact ni hai hai na inaweza kupimwa kwa kutumia immunoassays maalum ambayo kutambua molekuli nzima. PTH intact ni kawaida kupendekezwa katika mazoezi ya kliniki kwa sababu hutoa uwakilishi sahihi zaidi wa shughuli ya homoni katika mwili. Utafiti wa kiwango cha PTH (parathyroid hormone) unafanywa kwa kutumia teknolojia ya immunoassay. Immunoassay ni mtihani wa biochemical ambao hutumia sifa maalum za kuunganisha ya antibodies kwa molekuli za lengo, katika kesi hii, PTH. Vipimo hivi hutoa unyeti wa juu na maalum kwa kugundua na kuhesabu viwango vya PTH katika sampuli za damu. Utafiti wa immunoassay unaofanywa kwa njia ya radioimmunoassay (RIA) ni njia ya kawaida ya immunoassay ambayo hutumia molekuli za PTH zilizo na alama ya radioactive kama alama. Uchunguzi huo hupima kiasi cha PTH yenye mnururisho iliyounganishwa na kingamwili chake hususa. Kwa kulinganisha kuunganisha kwa mviringo wa kawaida, mkusanyiko wa PTH katika sampuli inaweza kuamuliwa. Ingawa RIA ni nyeti na maalum, imepungua katika umaarufu kutokana na wasiwasi juu ya taka za mnururisho na upatikanaji wa mbinu mbadala. Enzyme-linked immunosorbent assay (ELISA) ni njia ya uchunguzi wa kinga ya binadamu inayotumiwa kwa wingi na ambayo hutumia antibodies zilizounganishwa na enzyme kugundua PTH. Katika jaribio hili, mabadiliko ya rangi hutokea wakati substrate ya enzyme inaongezwa, na nguvu ya mabadiliko haya ya rangi ni moja kwa moja uwiano na kiasi cha PTH katika sampuli. ELISA ni rahisi, rahisi na rahisi kufanya, na ni chaguo la kawaida kwa ajili ya uchunguzi wa PTH. Electrochemistry Immunoassay (ECLIA) ni mbinu ya kisasa ya immunoassay ambayo hutumia electrochemiluminescence, uzalishaji wa mwanga unaotokana na athari ya electrochemical, kama njia ya kugundua. Katika ECLIA, molekuli za PTH zimeandikwa na kemikali ya chemiluminescent, ambayo hutoa mwanga wakati wa kukutana na umeme. Nguvu ya mwanga iliyotolewa ni sawa na kiasi cha PTH iliyopo katika sampuli. ECLIA inatoa unyeti wa juu, maalum, na mbalimbali pana ya nguvu. Chemiluminescent Immunoassay (CLIA) ni njia ya upimaji wa kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga ya kinga. Katika CLIA, molekuli za PTH zimewekwa alama na kiwanja cha chemiluminescent ambacho hutokeza mwanga wakati wa athari na substrate maalum. Mwanga intensity ni kupimwa na ni sawa na mkusanyiko PTH katika sampuli. CLIA ni nyeti sana, maalum, na haraka, na kuwafanya chaguo maarufu katika maabara nyingi za kliniki. Utafiti wa immunoassay umebadilisha kabisa tathmini ya PTH na kuchangia kuboresha utambuzi na usimamizi wa matatizo mbalimbali ya endocrine na metabolic. Maendeleo ya kuendelea katika teknolojia ya uchunguzi huahidi maboresho zaidi katika unyeti wa kugundua PTH, upendeleo, na ufanisi wa jumla. Matumizi ya kliniki: Kuna hali kadhaa za kliniki zinazohitajika kwa matumizi ya majaribio ya maabara ya PTH: - Parathyroidectomy kwa wagonjwa wanaosababisha hyperparathyroidism ya msingi. - Hypocalcemia kama matokeo ya pili ya thyroidectomy. - Kushuku ya hypercalcemia inayosababishwa na hyperparathyroidism. - Ugonjwa wa figo usio na mwisho. - Ugonjwa wa mifupa unaoshukiwa au uliothibitishwa. Uchunguzi wa ziada unaoweza kuamriwa pamoja na mtihani wa maabara ya PTH: - Kupima moja kwa moja viwango vya seramu ya kalsiamu. - Upimaji wa moja kwa moja wa viwango vya seramu inorganic phosphate. - Utaratibu wa mtihani na maandalizi ya mgonjwa Mtihani wa maabara ya PTH kwa ujumla unahitaji sampuli ya damu ya njaa iliyopatikana asubuhi (8 AM). Mgonjwa anapaswa kujiepusha na chakula usiku kucha, akinywa maji tu. Ni muhimu kwa wataalamu wa afya kuwa na habari ya dawa zozote ambazo mgonjwa anachukua kwa sasa, kwani dawa fulani zinaweza kuathiri viwango vya PTH. Uhifadhi wa sampuli na utunzaji: Sampuli za PTH lazima zifuatane na miongozo ya maabara kuhusu uhifadhi na utunzaji, ambayo kwa kawaida inahusisha kufungia mara moja na kuhifadhi kwa joto maalum. Sampuli inaweza kuhitaji kuhamishwa kwenye barafu kavu kwa maabara kuu kwa ajili ya uchambuzi. Kuhusu matibabu ya PTH kabla na baada ya mtihani, wataalamu wa afya wanapaswa kujadili sababu ya mtihani wa PTH na pia kumjulisha mgonjwa kuhusu mahitaji ya kufunga. Hii ni muhimu kwa sababu ulaji wa chakula unaweza kusababisha ongezeko bandia la seramu ya PTH. PTH ni muhimu katika utambuzi na usimamizi wa magonjwa mbalimbali ya tezi na figo. Uelewa kamili wa dalili za mtihani huu, taratibu, na matumizi ya kliniki inaruhusu watoa huduma za afya kuhakikisha utambuzi sahihi na huduma bora ya mgonjwa. LaGow B et al., eds. PDR Lab Mshauri Mwongozo wa jumla wa hatua za utunzaji kwa zaidi ya vipimo vya maabara 600 Toleo la kwanza. Montvale, NJ: Thomson PDR; 2007.