[The COVID-19 breaker : PCR to the rescue !] / La déferlante COVID-19 : la PCR à la rescousse ! Chronique d'une gestion de crise au Laboratoire de Microbiologie clinique du CHU de Liège.

Chronicle of a crisis management at the Clinical Microbiology Laboratory of CHU Liège The SARS-CoV-2 outbreak in December 2019 in China and its expansion across the world and Europe have requested the participation of clinical laboratories as major players in the diagnosis of COVID-19, to perform PCR tests mainly on nasopharyngeal swabs. In Belgium, the first confirmed COVID-19 patient was diagnosed in early February, the first of many, especially travelers returning from winter sports. In order to meet the ever-increasing demands for testing, the Clinical Microbiology Laboratory of the CHU of Liege had to adapt to this situation: firstly, by developing manual PCR tests and then automated solutions, permitting to increase the number of analyzes by ensuring a short turnaround time of results. Then, a system for the communication of results on a large scale has been set up, and finally solutions to deal with the lack of sampling devices have been found. This first wave of the pandemic has also highlighted an unprecedented solidarity within the institution. In this article, we recount the chronology of the management of this unprecedented health crisis within the Clinical Microbiology Laboratory of the CHU of Liege.

L'émergence du virus SARS-CoV-2 en décembre 2019 en Chine et son expansion à travers le monde et l'Europe ont sollicité la participation des laboratoires de Biologie clinique en tant qu'acteurs majeurs dans le diagnostic de la COVID-19, via la réalisation de tests PCR principalement sur des prélèvements nasopharyngés. En Belgique, le premier patient confirmé COVID-19 a été diagnostiqué début février, avant d'être suivi par de nombreux cas d'infections, initialement chez des vacanciers revenant des sports d'hiver. Afin de répondre à l'augmentation du nombre de tests, le laboratoire de Microbiologie clinique du CHU de Liège a dû s'adapter en développant des tests PCR, d'abord manuels puis automatisés. Ceux-ci ont permis d'augmenter le nombre d'analyses, tout en garantissant un temps de rendu des résultats court, en mettant en place un système de communication des résultats à grande échelle et en trouvant des solutions pour faire face à la pénurie des dispositifs de prélèvement. Cette première vague de la pandémie a aussi révélé une solidarité sans précédent au sein de l'institution. Dans cet article, nous retraçons la chronologie de la gestion de cette crise sanitaire inédite au sein du laboratoire de Microbiologie clinique du CHU de Liège.

Renal control of the peripheral uptake of exogenous gastrin in the dog.

The extraction of plasma gastrin during intravenous infusion of exogenous hormone has been measured in the head, gastrointestinal tract, or kidney of dogs submitted to sham surgery, evisceration, or binephrectomy without or with subsequent kidney transplantation. A significant gastrin extraction was demonstrated not only in the kidney, but also in the head and in the gastrointestinal tract; moreover, plasma gastrin extraction in the head and the bowel was considerably reduced by binephrectomy and was brought back to control values after subsequent kidney transplantation. A non-specific effect of surgery and a variation in peripheral blood flow seem to be excluded. Thus a control by the kidney of the peripheral removal of blood gastrin is evidenced, the mechanism of which remains hypothetical.

Influence of uranyl nitrate upon tubular reabsorption and glomerular filtration in blood perfused isolated dog kidneys.

The early changes in tubular reabsorption, glomerular filtration, blood flow and sodium excretion brought about by uranyl nitrate were investigated in isolated, blood-perfused dog kidneys during water diuresis. No significant changes in urine volume were observed; the decrease in fluid reabsorption was counterbalanced quantitatively by a reduction in glomerular filtration rate; only a small diminution of renal blood flow was found. The balance between reabsorption and filtration was observed as well when angiotensin action or prostaglandin synthesis were inhibited. The intrarenal venous pressure rose, suggesting that an increase in proximal intratubular hydrostatic pressure caused the decrease in filtration. Tubular back-leak of fluid, or back-diffusion, induced by the toxin, were excluded. The presence of natriuretic compounds in the urine was confirmed.

Connection between the changes in tubular reabsorption and in glomerular filtration rate induced by replacement of plasma sodium and chloride by isotonic mannitol.

Glomerular filtration and tubular reabsorption have been investigated comparatively in isolated blood-perfused dog kidneys, after addition to the blood of equal volumes of isotonic sodium chloride or isotonic mannitol. In the absence of antidiuretic hormone activity, the urine output showed no significant difference, while the glomerular filtration rate was lower in the presence of the mannitol load. The inhibition of fluid reabsorption was compensated by the decrease of filtration; a quantitative tubulo-glomerular equilibrium was evidenced. The fractional sodium excretion was decreased following the dilution by the mannitol load of plasma sodium and -chloride; this difference disappeared when the reabsorption in the diluting segment was inhibited by furosemide, suggesting that it depended on the rate of chloride reabsorption in this part of the tubule.

Furosemide, indomethacin and sodium excretion in isolated, blood-perfused dog kidneys.

Sodium excretion, renal blood flow and glomerular filtration rate were investigated in isolated, blood-perfused dog kidneys, thus excluding the interference of changes in body sodium and water balance. Four groups of experiments were performed : (a) control; (b) blood + indomethacin; (c) blood + furosemide; (d) blood + furosemide and indomethacin. The progressive vasodilatation due to the accumulation of prostaglandins was suppressed by indomethacin, the glomerular filtration rate remaining unchanged. The inhibition of prostaglandins synthesis was without influence on the natriuretic activity of furosemide. These results seem incompatible with an intrarenal mediation by prostaglandins of the diuretic effect of furosemide; moreover, this effect was dissociated from the changes in renal blood flow ascribed to renal prostaglandins.

The intrarenal regulation of sodium excretion in the dog.

1. The effect of sodium chloride-containing solution (saline) infusion on sodium excretion has been investigated in kidneys transplanted from donors into the neck vessels of other dogs (perfusors). The dogs (perfusors and donors) had been given sodium-enriched or sodium-poor diets ("loaded" and "deprived' dogs). 2. Three series of experiments were performed: (A) loaded perfusor, loaded donor; (B) deprived perfusor deprived donor; (C) deprived perfusor, loaded donor. 3. Kidneys from deprived dogs, transplanted into deprived perfusors, excreted less sodium after intravenous saline than kidneys from loaded dogs transplanted into loaded perfusors. However, the sodium excretion from the kidneys of loaded dogs transplanted into deprived perfusors was the same as that from the kidneys of loaded dogs transplanted into loaded perfusors. These differences suggest that intrarenal mechanisms are involved in the changes in sodium excretion which follow changes in dietary sodium balance. 4. The intraenal mechanisms included changes in glomerular filtration rate and fractional sodium reabsorption, but not changes in filtration fraction or renin release.

Influence of replacement of chloride by sulphate upon urine excretion and glomerular filtration rate in blood perfused isolated dog kidneys.

Tubular reabsorption was inhibited in isolated dog kidneys by the progressive substitution of plasma chloride by sulphate. In the absence of antidiuretic hormone activity, urine output remained unchanged owing to an equivalent decrease in glomerular filtration rate. This equilibrium was demonstrated under conditions of "saline natriuresis" and was not disturbed by furosemide. Although the impairment of glomerular filtration rate was accompanied by a decrease of total renal blood flow, the equilibrium was not disrupted by angiotensin antagonism. Sodium excretion was enhanced by low plasma chloride concentrations in the absence, but not in the presence of furosemide. The results are not compatible with a specific role of osmolality, sodium or chloride concentrations in the tubular fluid in the adjustment of glomerular filtration. Simultaneous changes in blood flow and tubular flow resistances might explain the results. It is suggested that, in contrast to the mechanism of tubulo-glomerular feedback found in individual nephrons of hydropenic animals, this intrarenal mechanism might serve to protect the organism against sodium loss under conditions of high intake.

Inhibition by indomethacin of the renal response to an acute saline load in the dog.

The kidneys of sodium-loaded dogs, treated by indomethacin before their transplantation to the neck vessels of sodium-depleted animals, lose their ability to increase the fractional excretion of sodium following an intravenous infusion of saline; they behave similarly to the kidneys of sodium-depleted dogs. Moreover, they become unable to potentiate the response of the kidneys of the sodium-depleted perfusors. The experimental conditions exclude a direct effect of the drug eo ipso. The results indicate that renal prostaglandins are involved in the adjustment of the renal response to saline loading, depending on the previous dietary sodium balance, and that they are related with the potentiating factors released into the blood by the kidneys of sodium-loaded animals.

Humoral control by the kidney of intestinal transport to sodium.

The impairment of water and sodium absorption by the jejunum following an acute saline load depends on the dietary balance of sodium, the mucosa-to-serosa unidirectional flux of this ion being modulated by a direct effect of the changes in blood concentration and by a humoral material of renal origin which itself is released as a consequence of either chronic or acute sodium loading. A possible interference of mineralocorticosteroids, angiotensin or antidiuretic hormone seems to be excluded. A positive correlation exists between mucosa-to-serosa sodium flux and glucose absorption. The kidney controls the exchanges of sodium and water in the jejunum as well as in the kidney itself by the way of an endocrine function.

Excretion of sodium and water by kidneys in situ and by transplanted kidneys following isotonic, hypotonic, iso-oncotic and hyperoncotic intravenous infusions in sodium-loaded and sodium-deprived dogs.

The excretion of sodium and water following isotonic, hypotonic, iso-oncotic and hyperoncotic intravenous infusions has been investigated in the kidneys in situ and in transplanted kidneys of narcotized dogs previously submitted to sodium-enriched or-deprived diets. The fractional excretion of sodium depended basically on the cumulative effect on the kidney of the changes in plasma oncotic pressure, plasma sodium concentration, and haematocrit. The differences in excretory responses of sodium-loaded or-deprived animals did not depend on differences in the distribution of infused fluids between intra- and extravascular compartments, but to the sensitivity of the kidney itself to the direct cumulative effect of these non-specific changes in blood composition.

Independance of glucagon and insulin handling by the isolated perfused dog kidney.

The effect of raising arterial plasma glucagon concentrations on kidney glucagon uptake was investigated using an isolated dog kidney perfused with whole blood. In addition, the effect of insulin on the magnitude of glucagon uptake by the kidney was studied at various glucagon concentrations. Renal vein plasma glucagon (V) has been found to be proportional to renal artery plasma glucagon (A). V and A were highly significantly correlated. In the absence of exogenous insulin infusion, V equalled 0.733 +/- 0.034 A, while in the presence of insulin V equalled 0.747 +/- 0.015 A. When kidney glucagon uptake was measured directly it increased as a function of arterial plasma glucagon. The calculated regression lines were similar in the presence and in the absence of insulin. The mean clearance rate of glucagon by the kidney was similar at low, medium or high concentrations of glucagon and was not affected by the presence of insulin at a mean concentration of 335.7 +/- 15.7 muU/ml. At this concentration of insulin, kidney insulin uptake was not affected by glucagon at concentrations ranging from 32 to 1600 pg/ml. Comparison of kidney glucagon uptake at similar arterial plasma glucagon concentrations, but with different renal plasma flows, indicated that kidney glucagon uptake is more dependant on arterial plasma glucagon concentration than on the quantity of glucagon entering the kidney per minute. It is concluded that: 1) kidney glucagon uptake increases as a function of arterial plasma glucagon concentration; 2) the clearance rate of glucagon is similar at low, medium or high arterial concentrations of glucagon; 3) at concentration of 300-350 muU/ml, insulin does not affect kidney glucagon uptake, and 4) at concentrations of glucagon up to 1600 pg/ml, renal insulin uptake is not affected by glucagon. These studies indicate that insulin and glucagon are handled independantly by the kidney of the dog.

Renal control of intestinal sodium and water transport in the dog.

The influence of an intravenous infusion of saline on the absorption of water and sodium by the jejunum has been investigated in dogs previously submitted to sodium-rich or poor diets. While the net intestinal transport was reduced in sodium-loaded animals, no response was observed in the sodium-deprived dogs, despite identical changes in arterial pressure, intravascular volume and blood dilution indexes. The intestinal response of sodium-deprived dogs became positive after transplanting to their neck vessels the kidneys removed from sodium-loaded animals, thus demonstrating that the presence in the blood of a humoral message of renal origin is required to permit the inhibition of net transport. The difference of the responses depended on the variations of the mucosa-to-serosa unidirectional flux. The net potassium transport did not change significantly. The experimental conditions made unlikely an interference of mineralocorticosteroids, angiotensin or antidiuretic hormone. The present results suggest that the kidney might modulate sodium transport in the jejunum, and perhaps elsewhere in the body, by the way of an additional endocrine function.

Hormones and non-specific humoral factors in the interferences between sodium, glucose and phosphate handling by dog kidney.

Some relationships between renal handling of sodium, glucose and phosphate have been investigated comparatively in dog kidneys studied "in situ", transplanted to the neck vessels of a perfusor animal, or perfused by a pump-oxygenator machine. The results can be summarized as follows: a) The values of tm of glucose per ml of glomerular filtration rate are not significantly different in the presence or in the absence of a perfusor animal, thus ruling out an hormonal modulation. b) An identical curvilinear regression relation between tmG and fractional excretion of sodium is found in the three types of experiments; the response to saline loading is identical; therefore an hormonal control of extrarenal origin is excluded. The differences in the decrease of tm glucose at high or low values of sodium excretion seem best explained by a coupling between glucose transport and one component of sodium transport which should be comparatively less influenced when the impairment of proximal reabsorption is high. c) A competition between glucose and phosphate excretion is observed in the isolated kidney; therefore it depends also at least for some part on intrarenal mechanisms. d) Insulin decreases phosphate clearance by direct renal action, probably by enhancing the tubular reabsorption of this ion as well as of sodium.