Diapositiva 1

Procalcitonin (PCT) is a 116 amino acid protein with a sequence identical to that of the
prohormone of calcitonin (32 amino acids) (Figure 2.1.1) (91, 136). Under normal
metabolic conditions, hormonally active calcitonin is produced and secreted in the Ccells of the thyroid gland after specific intracellular proteolytic procession of the
prohormone procalcitonin. In severe bacterial infections and sepsis, however, intact
procalcitonin is found in blood. Current research indicates that the orgin of procalcitonin
in these conditions is extrathyroidal.
The "Pre-pro-hormone"
After transcription of the CALC-1 gene, the primary transcript is processed into mRNA
encoding a 141-amino acid protein with a molecular weight of approximately 16 kDa.
This "precursor protein", preprocalcitonin, comprises a signal sequence, the N-terminal
region of procalcitonin (N-PCT), the middle sequence of calcitonin and the C-terminal
region of procalcitonin called "katacalcin" (Figure 2.1.3) (136).
Figure 2.1.5: Cleavage of preprocalcitonin by specific endopeptidases (according to 120).
Stabilità e conservazione
Unlike most cytokines, PCT is highly stable in collected blood samples. In-vitro plasma
PCT concentrations fall by approximately 12% at room temperature and by 6% at a
temperature of 4C over the 24-hour post-collection period (111). PCT can thus be
collected with routine laboratory specimens without any need for special storage
conditions. The samples should be stored in a refrigerator or, if storage or transport
times are prolonged or if any additional influence on the samples is to be avoided during
the scope of the studies being implemented, deep frozen until required for analysis. Both
the type of anticoagulation and the use of plasma or serum have no effect on PCT
measurements. However, a standardized collection technique, anticoagulation process
and storage procedures should be used for each hospital in order to minimize any
discrepancy in the values obtained (111).
cinetica
PCT induction is very rapid. PCT levels increase in response to a stimulus within 2-6
hours (see chapter 2.4). Following an initial increase, the decline in PCT values depends
on the balance between the plasma half-life and on new PCT production.
A half-life of approximately 20-24 hours is expected for PCT after a single, acute
stimulus. This was determined by means of the endotoxin experiments in healthy
subjects (46, 85, 137) and after accidental administration of a bacterially contaminated
solution for infusion (40). Under clinical conditions, the elimination half-lives have been
determined to lie within a higher range in many cases (101, 172). The elimination halflife of PCT is not significantly prolonged in patients with impaired kidney function (101,
172).
In patients with septic shock, plasma levels remain high due to on-going PCT
production. A fall in plasma levels to 50% of the initial concentrations has been reported
after an average of 2.4 days in patients who recovered from septic shock. Elevated
levels lasted for 27 days in patients with a fatal outcome (126).
Based on our experience, a fall of more than 30% in PCT values compared with the
previous day is correlated with a clinical improvement in septic patients (108). This
decline should, however, be observed over several days (at least three days) (see
chapter 3.3).
PCT reacts much more rapidly than C-reactive protein both in terms of the time to onset
of induction and in the interval between improvement in clinical conditions and a
clinically interpretable fall in values (106, 107, 109, 114).
The length of time to PCT synthesis and the type of induction show that the production
of PCT is closely correlated with inflammatory activation and is related to the induction of
proinflammatory cytokines. This correlation has been confirmed by clinical data (127).
According to current investigations, secondary induction of PCT by proinflammatory
cytokines is feasible although they are not the principal stimulus of PCT induction under
clinical conditions. Recent studies in mononuclear blood cells show that TNF-a and
other cytokines induce PCT mRNA. Bacterial endotoxins are the most potent stimulus
for PCT induction in this system (129). The clinical relevance of ex-vivo measurements
has not yet been confirmed as the cells tested do not release any noteworthy quantities
of PCT (94, 171).
Qual è l’utilità della misura della concentrazione di PCT nel plasma o altri fluidi
biologici
a. Nella DIAGNOSI di Sepsi e /o di batteriemia
b. Nel monitoraggio della sepsi
c. Nella durata del ricovero (malattia- sindrome)
d. Nella prognosi di severità o di outcome
fonte.: BRAHMS
Accuracy of sepsis diagnosis based on a
clinical model with and without PCT
Fonte: BRAHMS
PCT versus IL-6 and IL-8
Receiver operating characteristics (ROC) curves
comparing serum procalcitonin (PCT), interleukin 6 (IL-6)
and interleukin 8 (IL-8) for detection of sepsis on day
of admission to ICU.
Fonte: BRAHMS
KRYPTOR® uses TRACE (Time Resolved Amplified Cryptate Emission) technology, based on a non-radiative
transfer of energy.
This transfer takes place between two fluorescent tracers: europium cryptate (donor) and XL665 (acceptor).
The signal measured during the formation of the antigen-antibody complex is accompanied by an amplification.
KRYPTOR® assays are homogeneous, without separation or washing. It is thus possible to obtain data without
interrupting the immunological reaction. High-concentration samples are detected in the first few seconds of
incubation, and may be diluted by the appropriate dilution factor, then re-assayed automatically.
The molecules of PCT present in the assay samples are sandwiched between the antibodies. The intensity of the
signal is proportional to the amount of PCT. The shape of the standard curve is identical to that obtained by
immunometric methods.
For diagnosis of invasive bacterial infection/sepsis:
B·R·A·H·M·S PCT-Q (rapid assay)
B·R·A·H·M·S PCT LIA (manual assay)
LIAISON®B·R·A·H·M·S PCT (automated assay)
For diagnosis of LRTI and invasive bacterial infections/sepsis:
B·R·A·H·M·S PCT KRYPTOR (automated assay)
ELECSYS® B·R·A·H·M·S PCT (automated assay)
VIDAS® B·R·A·H·M·S PCT* (automated assay)
B·R·A·H·M·S PCT sensitive LIA (manual assay)
Un vantaggio essenziale da un puntoi di vista clinico e di laboratorio;
automatizzata, pronta per l’uso giorno per giorno
Ma nel 2007: due metanalisi hanno negato pressochè valore al
dosaggio di PCT come mezzo per la diagnosi precoce di sepsi.
vediamole
Eppure continuano a comparire lavori positivi sull’uso della procalcitonina
nella diagnosi di sepsi e nel monitoraggio di essa e di altre infezioni
sistemiche e localizzate
Il mio gruppo ha seguito questa strada