José Herrera, Estela Ávila, Crispín Marín, Bernardo Rodríguez‐Iturbe, Impaired creatinine secretion after an intravenous creatinine load is an early attribute of the nephropathy of sickle cell anaemia, Nephrology Dialysis Transplantation, Quantity 17, Concern 4, April 2002, Pages 602–607, https://doi.org/10.1093/ndt/17.4.602
Summary
Introduction
We’ve got just lately reported that the tubular secretion of creatinine is elevated a number of‐fold after a creatinine load, and that this response is impaired in circumstances related to discount in renal functioning mass [1,2]. Research in regular people demonstrated that maximal U/P creatinine and creatinine clearance/inulin clearance ratios have been discovered with acute elevations of serum creatinine to 500–700 μmol/l and that these ranges have been obtained with a single intravenous bolus of 88.4 μmol (10 mg) of creatinine per kg of physique weight [2]. On the premise of those outcomes, a comparatively easy tubular stress take a look at (TST) was developed to guage the capability of the kidney to extend its creatinine secretion. This take a look at proved helpful to discriminate between teams of people with regular ranges of serum creatinine however a special variety of nephron models: regular people with two kidneys, regular people with one kidney (kidney donors), and transplant sufferers with regular renal perform [2]. These findings steered that lack of the secretory reserve capability for creatinine anteceded the impairment of glomerular filtration within the pure historical past of progressive renal illness. Consequently, it raised the chance that the TST may have medical relevance within the analysis of the non‐azotaemic affected person.
A gaggle of sufferers in whom it might be explored if the reserve capability for creatinine secretion is impaired in hyperfiltering kidneys is the group of sufferers with sickle cell anaemia (SCA). The sufferers with homozygous sickle haemoglobin (SS) illness current quite a lot of renal haemodynamic, useful and structural abnormalities [recently reviewed in 3–5], however, pertinent to this investigation, these sufferers have elevated glomerular filtration fee (GFR) and renal plasma circulation, and lowered serum creatinine ranges in childhood and adolescence [6–7], adopted by a subsequent deterioration of renal perform that’s often irregular after the age of 40 [8,9]. When vital proteinuria or azotaemia are current, roughly half of the sufferers with SCA will go on to finish‐stage renal illness in lower than 2 years [10]; renal failure nonetheless accounts for 18% of the deaths in grownup sufferers with SCA [11]. Subsequently, the detection of abnormalities in renal perform that precede proteinuria and adjustments in GFR might not solely give some perception on the mechanisms of development of renal injury but additionally might have medical significance.
The current research was executed to reply a particular query: is the capability to extend creatinine secretion in response to a creatinine load impaired in sufferers with SCA who nonetheless have a standard or supranormal ranges of GFR? To deal with this problem we evaluated the response to the TST in younger sufferers with SS haemoglobin illness.
Sufferers and strategies
Sufferers with sickle cell anaemia and regular controls
The sufferers with SCA (homozygous haemoglobin SS illness) have been volunteers recruited from the outpatient Sickle Cell Clinic within the Hospital Universitario and Instituto Hematológico de Occidente, Maracaibo. They have been 16 sufferers with a median age of 23 years (vary 15–40 years) with regular renal perform. Their haemoglobin ranged from 7.4 to 11.6 g/dl. The routine urine analyses have been dipstick damaging for protein in 14 sufferers and hint constructive in a single and +1 in a single. All of them had damaging serologic markers for viral hepatitis and human immunodeficiency virus. All had regular fasting blood sugar and their blood stress was regular.
The conventional controls have been 20 volunteers, median age 23.5 years (vary 18–43 years) with regular haematological and biochemical blood profiles and regular urine evaluation. Fourteen of those regular topics had been reported as a management group in a earlier research of the TST [2]. All people studied denied voiding difficulties and full bladder emptying by voluntary voiding was documented by ultrasound sonography.
For at the least 2 weeks previous to the research, the sufferers and the controls weren’t allowed to take drugs that modify renal haemodynamics or block the renal response to a protein or creatinine load, resembling non‐steroidal anti‐inflammatory medication, nor medication that intrude with the tubular secretion of creatinine, resembling trimethoprin sulfamethoxasol or cimetidine, nor medication that intrude with the Jaffe’s response, resembling cephalosporins or ascorbic acid. The urine of all topics within the research was strip take a look at damaging for ketones.
The protocol of the research was permitted by the Ethics Committee of the Division of Medication.
Tubular stress take a look at (TST)
The sufferers arrived at 8 am to the Renal Laboratory. The final meal was eaten 12 h earlier than the research (8–9 pm the earlier evening) and after this meal solely free water consumption was permitted. Diuresis was stimulated by the ingestion of 20 ml/kg physique weight of water and maintained by consuming each 30 min the quantity eradicated within the earlier 30‐min interval. Upon arrival, 30 μCi of [125I]iothalamate (Gliofil‐125, Cypros Pharmaceutical Corp., Carlsbad, CA), in 0.05 ml saline resolution with 0.02 ml 1:1000 epinephrine resolution was injected subcutaneously within the forearm. As reported beforehand [2], this resulted in secure serum cpm counts all through the research. Forearm veins have been cannulated and 1 h after the subcutaneous injection of [125I]iothalamate, three 30‐min clearance durations have been executed as baseline (unstimulated, PRE) research. All urinary collections have been executed by supervised voluntary voiding. Then, 88.4 μmol of creatinine (Sigma Chemical Co. St. Louis, MO) per kg physique weight have been dissolved in 100 ml of 5% dextrose and water sterile resolution for intravenous use, handed by way of a single‐use millipore filter (sterile acrodisk 0.2 μm, Gelman Sciences) and administered intravenously in 10 min. The creatinine infusion was effectively tolerated and there have been no pyrogenic reactions.
After the creatinine bolus, urinary collections have been executed, first from time 0 (finish of the creatinine infusion) to fifteen min after which, in three successive collections durations of 30 min every. Clearance calculations have been executed in these three assortment durations utilizing blood samples that bracketed every urinary assortment.
As described beforehand [2], the preliminary 15 min after the top of the creatinine infusion are unreliable for clearance research as a result of throughout this time there’s a steep exponential lower in serum creatinine (Pcr), however after the preliminary 15 min the Pcr decreases slowly in nearly linear vogue and, as reported beforehand [2], clearance calculations utilizing the averaged Pcr(a‐Pcr)=[Pcri+Pcrf]/2, the place i and f are preliminary and remaining, respectively, creatinine concentrations of the corresponding clearance interval) are virtually just like the calculations utilizing the exponential expression (e‐Pcr=exp[(lnPcri+lnPcrf)/2]. Subsequently, calculations of GFR, creatinine clearance (Ccr), urinary creatinine excretion fee (UcrV) and tubular secretion of creatinine (TScr) have been executed in 30‐min successive clearance durations 15–45 min publish‐load (Interval A), 45–75 min publish‐load (Interval B) and 75–105 min publish‐load (Interval C). Knowledge was evaluated individually for Interval A and for the imply of the three stimulated durations ([A+B+C]/3).
[125I]iothalamate clearance and Ccr have been calculated by the usual formulation (UxV/Px). [125I]iothalamate clearance was thought of equal to the GFR. The TScr was estimated by the distinction between the UcrV and the filtered creatinine (GFR×Pcr): TScr=UcrV−(GFR×Pcr).
The clearance of creatinine by secretion is CTScr=TScr/Pcr.
The clearances have been corrected by 1.73 m2 floor space. UcrV and TScr have been corrected for physique weight.
The per cent excreted of the exogenous creatinine load was estimated subtracting the baseline (pre‐load) urinary creatinine excretion from the publish‐load urinary creatinine excretion within the corresponding interval: (Stimulated UcrV−Baseline UcrV)×100/creatinine load.
Chemical determinations
I125 radioactivity in plasma and urine was counted with a gamma counter (LKB 1282 Compugamma). Creatinine determinations have been executed by autoanalyser methodology (Specific Extremely Plus, Ciba‐Corning) since research in our laboratories with oral creatinine hundreds had beforehand proven that the ratios of ‘true’ (chromogen free) Ccr/Autoanalyser Ccr weren’t considerably totally different from 1 [1].
Statistical calculations
Comparisons between the affected person and management teams have been executed by unpaired evaluation of variance (ANOVA) adopted by a number of comparisons Tukey‐Kramer publish‐exams. Adjustments from baseline determinations of Ccr and Cin in SCA sufferers and in controls have been evaluated with repeated measures ANOVA adopted with Dunnett publish‐exams. A industrial statistical bundle (GraphPad Instat, San Diego, CA) was used for statistical evaluation. Knowledge are expressed as imply values±SD. Two‐tailed P values <0.05 have been thought of statistically vital.
Outcomes
The SCA sufferers have been of comparable age with the management group however had a decrease physique weight (Desk 1). Their urinary osmolarity after 12‐h water deprivation was 427±45.8 mOsm/l. Their systolic blood stress was 117±7.2 mmHg and their diastolic blood stress 65±8.8 mmHg.
The baseline knowledge within the SCA sufferers and within the management group are proven in Desk 1. Sufferers with haemoglobin SS illness had increased GFR and Ccr and decrease Pcr and TScr within the baseline research than the management people. Urinary creatinine excretion and Ccr/GFR ratio weren’t totally different in management and sufferers (Desk 1).
The GFR didn’t change throughout the TST in SCA sufferers nor in controls (Determine 1). In distinction, the Ccr elevated considerably in SCA sufferers and in controls with respect to pre‐take a look at baseline ranges, however the increment in Ccr discovered within the SCA sufferers (Interval A/Pre=1.17±0.19) is considerably much less (P<0.05) than the increment noticed in controls (Interval A/Pre=1.30±0.14) (Determine 2). Outcomes obtained with the TST are proven in Desk 2. Pcr ranges at time 0 (finish of creatinine infusion) are comparable in SCA sufferers (628±228 μmol/l) and in regular controls (621±155 μmol/l). The Pcr values decreased to ranges of 168±38.5 μmol/l within the sufferers and solely to 267±52.2 μmol/l in regular controls in Interval A (P<0.01). Nevertheless, these values represented comparable increments with respect to pre‐take a look at values proven in Desk 1; the interval A/baseline Pcr ratios have been 3.07±0.57 within the SCA sufferers and three.15±0.75 in controls. As proven in Desk 2, TScr ensuing from the TST was decreased within the SCA sufferers in Interval A (P<0.001) and within the imply publish‐stimulation determinations (P<0.001), (Desk 2). Serial determinations of TScr are proven in Determine 3. Throughout Interval A, the increment in urinary creatinine resulted within the excretion of 10.9±4.8% of the administered creatinine in management people, and 12.2±3.7% in SCA sufferers (P NS). Nevertheless, as proven in Determine 4, the increment in UcrV within the management people (81.5±26.6%) was principally the results of tubular secretion of creatinine whereas within the SCA sufferers, the contribution of tubular secretion was considerably much less (42.6±16.6%). Through the TST, controls and the SCA sufferers eradicated 40.4±8.5% and 40.2±14.5%, respectively, of the creatinine administered within the take a look at, however as famous earlier than, the contribution of the TScr to the UcrV was considerably decrease within the SCA sufferers.
To guage the chance that the decreased TScr within the SCA sufferers was the results of inadequate stimulation of the tubular secretory capability on account of decrease Pcr values throughout the publish‐stimulation durations, a separate evaluation was made restricted to the info obtained throughout these research durations through which the same vary of Pcr ranges existed in management people and in SCA sufferers. These knowledge are given in Figures 5A and 5B, exhibiting respectively the TScr and the CTScr in seven SCA sufferers and 16 management people in durations through which Pcr ranged from 176.8 μmol/l to 265.2 μmol/l (2–3 mg/dl). To keep away from over‐illustration of a given particular person, we utilized in every case the common of the info obtained in a given particular person within the chosen Pcr vary. On this method, every particular person (management or SCA affected person) contributed with no a couple of level for evaluation. As demonstrated in these figures (5A and 5B), SCA sufferers had considerably (P<0.001) decrease stimulated tubular secretion of creatinine than normals.Dialogue – “creatinine 7.4”
Sufferers with SCA have quite a lot of renal structural and useful abnormalities that progress with age. Younger sufferers with haemoglobin SS illness have elevated renal plasma circulation and glomerular filtration fee, which is ceaselessly lowered after the age of 40 [8,9]. The ultrafiltration coefficient (Kf) has been discovered to be decreased in affiliation with renal insufficiency [12] in addition to elevated in proteinuric SCA sufferers [13]. Research from a number of different teams have demonstrated a number of distal nephron alterations, together with decreased concentrating capacity [14], incomplete renal tubular acidosis [15], and impaired potassium secretion [16]. In distinction, sure proximal tubular capabilities, such because the secretion of PAH and uric acid [17,18] have been discovered to be elevated above regular ranges.
In settlement with earlier research, our baseline knowledge confirmed that SCA sufferers had regular or supranormal ranges of GFR and decrease than regular Pcr ranges (Desk 1).
The baseline TScr was decrease within the SCA sufferers than in controls. This discovering is opposite to the elevated values which might be quoted in literature evaluations [5,18] and deserve some concerns. To our information, the one research that evaluated the tubular secretion of creatinine (unstimulated) is the research of de Jong et al. [7]. This elegant investigation explored the haemodynamic results of prostaglandin synthesis inhibition in SCA and located that the baseline tubular secretion of creatinine was elevated in these sufferers. Nevertheless, the discrepancy within the conclusions relating to the baseline TScr of their work [7] and on this investigation could also be due, at the least partially, to the tactic of estimation of creatinine secretion. De Jong et al. [7] evaluated the fractional creatinine excretion [(Ccr/Cin)×100] and their knowledge confirmed that it was 134% in SCA sufferers and 108 in controls. We estimated TScr because the distinction between urinary creatinine excretion minus filtered creatinine (see strategies) and located it decreased in SCA sufferers. Ccr/Cin ratios in our baseline research point out that fractional creatinine excretion in our sufferers was 118±24% and 124±19% in our management topics, and this distinction will not be statistically totally different. Moreover, if we examine our baseline Ccr/Cin ratios with these of de Jong et al. [7], we discover that the values in SCA sufferers will not be statistically totally different (de Jong et al. =134±31, current work =118±24, P=0.13), whereas in distinction, the management group in de Jong et al.’s work [7] had fractional creatinine clearances decrease than within the current research (de Jong et al. =108±14, current work =124±19, P=0.02). Subsequently, it seems that when our knowledge is calculated in the same method as in de Jong et al.’s, the distinction is within the management topics, quite than within the SCA sufferers.
Maximal stimulation of the creatinine secretory capability has been discovered to be impaired in circumstances related to subclinical discount in nephron mass and a tubular stress take a look at, consisting within the sequential analysis of the TScr after a single intravenous bolus of creatinine, has been proposed to check the tubular useful reserve [2]. The medical usefulness of this take a look at is dependent upon the premise that renal sufferers have irregular responses earlier than their Pcr is elevated and, ideally, earlier than their glomerular filtration fee is lowered. Since younger SCA sufferers ceaselessly have supranormal GFR earlier than a lot of them develop progressive segmental glomerulosclerosis [19], we determined to check if TST could be impaired in these sufferers.
The administration of a standardized dose of 88.4 μmol of creatinine per kg (TST) given intravenously resulted in comparable ranges of Pcr in controls and SCA sufferers on the finish of the infusion (Time 0 in Desk 2). Nonetheless, the SCA sufferers had considerably decrease Pcr ranges than controls within the clearance durations of the TST on account of their elevated GFR.
A number of observations have been made with the TST. The primary statement was that GFR remained unchanged throughout the TST at values that have been uniformly increased within the SCA sufferers than in controls (Determine 1). Fairly secure GFR ranges throughout the TST have been anticipated from the preliminary description of the take a look at [2]. In distinction to the GFR findings, a transparent distinction existed within the response of Ccr to the TST (Determine 2): whereas a supranormal Ccr elevated barely within the SCA sufferers, the conventional controls elevated sharply the Ccr throughout interval A, at which era their Ccr reached ranges that have been just like these of the SCA sufferers (Desk 2 and Determine 2) and, subsequently, decreased in direction of pre‐stimulation values.
The principal parameter explored with the TST is the TScr. As proven within the serial values of TScr in Determine 3 and within the summarized knowledge in Desk 2, the sufferers with SCA had about 40% discount of their creatinine secretory fee in Interval A with respect to the conventional response. A discount of the TScr within the TST might be on account of decreased tubular reserve capability or to inadequate stimulation of TScr throughout the TST. Whereas it’s conceivable that maximal tubular secretion of creatinine in SCA nephropathy would require increased ranges of Pcr or longer durations of creatinine administration, the info obtained in regular topics and in topics with lowered renal mass signifies that maximal Ucr/Pcr ratios are related to a bolus of intravenous creatinine that produces, on the finish of the infusion, Pcr values of 500–700 μmol/l [2]. In truth, Pcr ranges on the finish of the creatinine infusion (time 0, Desk 2) have been within the desired vary. Nonetheless, the next discount of Pcr was extra pronounced in SCA sufferers (interval A and imply publish‐stimulation values in Desk 2), seemingly ensuing from their increased filtration fee. Subsequently, the potential of inadequate stimulation of creatinine secretion needs to be thought of in SCA sufferers. It must be realized that whereas the Pcr are decrease in SCA sufferers in Interval A (Desk 2), the increment with respect to baseline values (Interval A/Baseline) is comparable in sufferers and controls (SCA sufferers =3.15±0.75, controls 3.07±0.57). Nonetheless, it’s attainable that absolutely the degree of Pcr, quite than its increment, is the figuring out stimulus for the secretion of creatinine. Subsequently, to guage the TScr at comparable ranges of Pcr, we analysed the person clearance durations through which each the SCA sufferers and the conventional controls had Pcr in the same vary: 176.8–256.2 μmol/l (2–3 mg/dl). These knowledge are proven in Figures 5A and 5B, and exhibit that on this evaluation the TScr and the CTScr have been additionally considerably lowered in SCA sufferers. As well as, tubular secretory response was not associated to the GFR ranges in early SCA nephropathy since sufferers with GFR >120 ml/min didn’t have considerably totally different stimulated TScr than sufferers with decrease GFR values.
The reason for impaired TST in SCA can’t be outlined from the current research. The nephropathy of SCA is a fancy situation through which sure tubular capabilities, resembling damaging water clearance, potassium secretion and urinary acidification are impaired and different tubular capabilities, resembling renal plasma circulation and uric acid secretion are augmented. It should be emphasised that our findings concern particularly the capability of the tubule to answer creatinine stimulation, quite than to the unstimulated standing of tubular creatinine secretion. On this sense, a TST is extra alike to a water deprivation take a look at that uncovers impairment within the capability to maximally focus the urine. Such a defect can also be an early attribute of SCA nephropathy and was in reality demonstrated in our sufferers who had a imply urinary osmolarity of 427 mOsm/l after 12‐h dehydration. Latest investigations point out that repeated durations of ischaemia are related to native inflammatory response in tubulointerstitial areas within the transgenic sickle cell mice [20]. If comparable episodes happen within the human they might conceivably have an effect on earlier the capability to answer stimulation than the baseline perform.
In conclusion, the TST demonstrates that younger SCA sufferers with regular or supranormal GFR have a lowered capability to extend their TScr. A diminished tubular secretory useful reserve represents an early occasion within the nephropathy of sufferers with haemoglobin SS illness. Whereas it’s temping to contemplate that irregular TST may predict subsequent deterioration of glomerular filtration within the subset of SCA sufferers that develop finish‐stage renal illness, there is no such thing as a proof this present day to assist this chance.
Correspondence and offprint requests to: Dr B. Rodríguez‐Iturbe, Apartado Postal 1430, Maracaibo 4001‐A, Venezuela. Electronic mail: [email protected]
Monetary assist for the research was obtained from the Asociación de Amigos del Riñón (Maracaibo) and Fundacite‐Zulia.
References
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