The measurement of urinary hydroxyurea in sickle cell anaemia

Hydroxyurea is increasingly used in the treatment of sickle cell disease (SCD) although there is little evidence on how best to monitor treatment and compliance. It is also not known why 10-50% patients do not benefit from the drug and whether some of this resistance is because of pharmacokinetic factors. We have developed an assay using mass spectrometry (MS) to measure urinary concentrations of hydroxyurea. We have used this assay to study 12 children and six adults with SCD taking hydroxyurea and found that urinary hydroxyurea was present for at least 12 h following tablet ingestion. Thirty-five urine samples were analysed that were expected to contain hydroxyurea, based on the reported timing of the last dose and hydroxyurea was detected in 29 (83%) of these. There were also marked differences in urinary hydroxyurea concentrations, suggesting pharmacokinetic variability may explain some of the differences in response to hydroxyurea. Urine samples were also analysed by MS for penicillin metabolites and 43 of the 57 (75%) contained phenoxyacetate, suggesting the ingestion of penicillin within the last 12 h. These assays are potentially useful to study hydroxyurea metabolism further, develop optimal dosing regimes and monitor compliance with treatment.

Delayed hemolytic transfusion reaction/hyperhemolysis syndrome in children with sickle cell disease

OBJECTIVE

Alloimmunization in patients with sickle cell disease (SCD) has a reported incidence of 5% to 36%. One complication of alloimmunization is delayed hemolytic transfusion reaction/hyperhemolysis (DHTR/H) syndrome, which has a reported incidence of 11%. In patients with SCD, clinical findings in DHTR/H syndrome occur approximately 1 week after the red blood cell (RBC) transfusion and include the onset of increased hemolysis associated with pain and profound anemia. The hemoglobin (Hb) often drops below pretransfusion levels. In many reported adult cases, the direct antiglobulin test (DAT) remains negative and no new alloantibody is detected as the cause for these transfusion reactions. To date, few pediatric cases have been reported with this phenomenon. The objective of this study was to describe the clinical and laboratory findings of a case series in children who had SCD and experienced a DHTR/H syndrome at our institution.

METHODS

An 11-year retrospective chart review of patients with discharge diagnosis of SCD and transfusion reaction was performed. DHTR/H syndrome was defined as the abrupt onset of signs and symptoms of accelerated hemolysis evidenced by an unexplained fall in Hb, elevated lactic dehydrogenase, elevated bilirubin above baseline, and hemoglobinuria, all occurring between 4 and 10 days after an RBC transfusion. Patient characteristics, time from transfusion, symptoms, reported DAT, new autoantibody or alloantibody formation, laboratory abnormalities, and complications were recorded. Patients with acute transfusion reactions were excluded.

RESULTS

We encountered 7 patients who developed 9 episodes of DHTR/H syndrome occurring 6 to 10 days after RBC transfusion. Each presented with fever and hemoglobinuria. All but 1 patient experienced pain initially ascribed to vaso-occlusive crisis. The DAT was positive in only 2 of the 9 episodes. The presenting Hb was lower than pretransfusion levels in 8 of the 9 events. Severe complications were observed after the onset of DHTR/H: acute chest syndrome, n = 3; pancreatitis, n = 1; congestive heart failure, n = 1; and acute renal failure, n = 1.

CONCLUSIONS

DHTR/H syndrome occurs in pediatric SCD patients, typically 1 week posttransfusion, and presents with back, leg, or abdominal pain; fever; and hemoglobinuria that may mimic pain crisis. Hb is often lower than it was at the time of original transfusion, suggesting the hemolysis of the patient's own RBCs in addition to hemolysis of the transfused RBCs; a negative DAT and reticulocytopenia are often present. Severe complications including acute chest syndrome, congestive heart failure, pancreatitis, and acute renal failure were associated with DHTR/H syndrome in our patients. DHTR/H in the pediatric sickle cell population is a serious and potentially life-threatening complication of RBC transfusion. It is important to avoid additional transfusions in these patients, if possible, because these may exacerbate the hemolysis and worsen the degree of anemia. DHTR/H syndrome must be included in the differential of a patient who has SCD and vaso-occlusive crisis who has recently had a transfusion.

Risk factors for microalbuminuria in children with sickle cell anemia

PURPOSE

To determine the prevalence of microalbuminuria and to establish clinical characteristics associated with microalbuminuria in children with sickle cell anemia.

PATIENTS AND METHODS

Urine samples of all children (homozygous SS) followed in the Medical College of Georgia's Children's Medical Center Sickle Cell Clinic were screened for microalbuminuria. Random samples were obtained from continent patients at routine office visits between September 1996 and November 1999. A retrospective chart survey was performed to determine clinical correlates for microalbuminuria. Medical records were reviewed for age, sex, hemoglobin, and episodes of pneumonia, pain, aplasia, acute chest syndrome, priapism, and avascular necrosis. Demographic and clinical variables were compared with microalbuminuria by univariate and multivariate logistic regression.

RESULTS

One hundred forty-two patients ages 21 months to 20 years made up the study group. The prevalence of microalbuminuria was 19%. Both increasing age and a lower hemoglobin level were found to correlate with microalbuminuria. By multivariate analysis, boys with microalbuminuria were likely to have a lower hemoglobin level and girls with microalbuminuria were likely to be older. None of the following factors were significantly related to microalbuminuria: pain, pneumonia, acute chest syndrome, priapism, avascular necrosis, or aplastic episodes.

CONCLUSIONS

Microalbuminuria is strongly and directly related to age and strongly and inversely related to hemoglobin levels. Identification of risk factors for microalbuminuria may allow earlier intervention to prevent renal complications in patients with sickle cell disease.

Glomerular filtration rate in Nigerian children with homozygous sickle cell disease

The study proposed to assess glomerular filtration rate as determined by endogenous creatinine clearance in steady state Nigeria children with homozygous sickle cell disease and normal controls. Twenty-four hours urinary creatinine clearance was estimated over a 6-month period in 54 steady-state homozygous sickle cell disease and 57 normal control children aged 5 to 13 years. Each child was admitted and a 24-hour urine sample (8.00 am to 8.00 am) was collected both for volume measurement and creatinine concentration determination. Blood was also collected from each child 30 minutes to end of urine collection for plasma creatinine concentration determination, haematocrit and reticulocyte counts. The results were compared between the two groups of children using student's t-test and the chi (X2) square test where necessary. The mean glomerular filtration rates +/- SD (ml/min/1.73 M2) for homozygous sickle cell disease children and normal controls were not significantly different (p > 0.05). Glomerular filtration rate did not differ significantly between the age groups in both patients and normal controls; haematocrits correlated weakly with glomerular filtration rates in the patients (r = +0.213; p < 0.001). Nigerian children with homozygous sickle cell disease who are in steady states have normal glomerular filtration rate that is hardly influenced by increasing age and low haematocrit level.

Ascorbate levels in red blood cells and urine in patients with sickle cell anemia

Ascorbic acid can be important in sickle cell anemia (SCA) because significant oxidative stress occurs in the disease. Ascorbate could contribute to reduction of the increased oxygen free radicals generated in sickle red blood cells (SRBC) and to the recycling of vitamin E in the cells, while renal loss could contribute to the low plasma levels. Evaluation of red blood cell (RBC) and urine ascorbate in SCA has not been reported. Results showed (1) ascorbate levels in SRBC were similar to those in normals; (2) urine ascorbate excretion was increased in 36% of patients; (3) plasma levels of ascorbate were decreased.

CONCLUSIONS

(1) Ascorbate is present in SRBC, most likely due to ascorbate recycling, despite increased free-radical generation. (2) The increase in renal excretion may contribute to the low plasma levels of ascorbate. (3) The presence of ample ascorbate in SRBC and decreased plasma ascorbate suggests that ascorbate movement across the SRBC membrane may differ from normal RBC.

Prevalence of microalbuminuria in children with sickle cell disease

Renal involvement is common in homozygous sickle cell disease (HbSS), including glomerular hypertension and hypertrophy similar to that seen in rodent models of ablative nephrectomy and stage I diabetic nephropathy (DN). The proteinuria in the rodent models is attenuated by angiotensin converting enzyme inhibition (ACEI). Microalbuminuria (MA) is a sensitive marker for renal involvement in DN prior to the development of proteinuria, and is also attenuated with ACEI. Elevated urinary microalbumin/creatinine ratios (U Alb/Cr) >20 mg/g Cr are reported in 39%-43% of adults with HbSS, and studies are ongoing in this age group to assess the effect of attenuated proteinuria by ACEI on long-term renal function. The purpose of this study was to prospectively investigate the prevalence of MA in children with HbSS and determine factors which affect its expression. U Alb/Cr values were measured on spot urine samples in 102 children (aged 2-18 years, mean 9.47+/-4.62, M:F=53:49) by rate nephelometry. Children with prior known proteinuria, hypertension, or fever/pain episode in the last 15 days were excluded. MA was present in 26.5% of all children with HbSS. However, in children between the ages of 10 and 18 years, the prevalence was 46% (similar to the prevalence in adults). There was a strong correlation between patient age and prevalence of MA (P<0.0001) by both univariate and multivariate analysis. However, pain frequency, hospitalization, transfusion program, ferritin levels, and Cr clearance (C(Cr)) did not correlate with prevalence, although C(Cr) (as estimated by Schwartz formula) was elevated in all. We conclude that the prevalence of MA in the 2nd decade of life is similar to that in adults.

Eicosanoids in sickle cell disease: potential relevance of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid to the pathophysiology of vaso-occlusion

The monohydroxyeicosanoid 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), which is derived from oxygenation of arachidonic acid by 12-lipoxygenase, is one of the major metabolites in platelets. In a recent study, we have showed that this eicosanoid stimulated basal sickle-red-cell-endothelial-cell adhesion. To understand the pathophysiologic significance of 12-HETE, we measured the levels of this eicosanoid in plasma and urine from children with sickle cell disease. We found that as compared with controls, plasma 12-HETE levels are increased in patients with sickle-cell disease in the steady state, and are increased further during vaso-occlusive crises. Urinary 12-HETE levels were also increased during the steady state. We also assessed plasma levels of soluble P-selectin (another potential marker for platelet activation), and found changes in the levels of this marker similar to those seen with plasma 12-HETE. In additional studies, we found that 12-HETE enhanced hypoxia-induced sickle-red-cell-endothelial adherence, and that this effect was mediated by potentiation of agonist-induced upregulation of the expression of the mRNA for vascular cell adhesion molecule-1 (VCAM-1) in endothelial cells. Because 12-HETE appears to enhance both basal and agonist-induced sickle-red-cell adhesion, this metabolite could potentially play a role in the pathogenesis of the vaso-occlusive crisis (VOC) in sickle-cell disease.

[Arterial pressure and urinary excretion of albumin in adults with sickle cell disease]

OBJECTIVE

The increase of urinary albumin excretion could be associated with morbidity in patients with sickle cell disease. The objective of this study was to evaluate the relation between blood pressure and urinary albumin excretion, and to estimate the prevalence of hypertension according to the level of urinary albumin excretion.

METHODS

A cross-sectional study was carried in 77 patients with sickle cell disease (48 patients with haemoglobin SS, 29 with haemoglobin SC) et 30 controls with haemoglobin AA. The patients with sickle cell disease were divided into 3 groups according to urinary albumin excretion: less than 30 mg daily (group I: normoalbuminuria); from 30 to 300 mg daily (group II: microalbuminuria); above 300 mg daily (group III: macroalbuminuria). All AA selected controls had normoalbuminuria (group IV).

RESULTS

In normoalbuminuric patients, the average of blood pressure was significantly lower in patients with sickle cell disease than in controls (respectively 115.0 +/- 8.1 vs 132.1 +/- 15.1, p = 4.10(-6) for systolic pressure and 67.2 +/- 8.0 vs 78.8 +/- 9.8 mmHg, p = 10(-4) for diastolic pressure). There was a positive relation between urinary albumin excretion, even moderate (values < or = 300 mg daily) and blood pressure in SS patients (r = 0.40, p < 0.02 for systolic and r = 0.54, p < 0.01 for diastolic pressure) and in SC patients (r = 0.74, p < 0.001 and r = 0.58, p < 0.01). The prevalence of hypertension was 0% in group I, 25% in group II and 66% in group III.

CONCLUSION

The positive association between blood pressure and urinary albumin excretion suggests that the latter should be taken into account in sickle cell disease's follow up.

Decreased urinary excretion of beta-glucuronidase in sickle cell anemia in Nigeria

The activities of five lysosomal hydrolases--namely beta-glucuronidase, beta-hexosaminidase, beta-galactosidase, alpha-galactosidase, and alpha-mannosidase--were measured in the plasma and urine of children (ages, 7 to 15 years) with sickle cell anemia (n = 11) and controls (n = 11) from Jos, Nigeria. The presence of SS hemoglobin was confirmed by electrophoresis of red cell hemolysates. Albuminuria was absent in all of the patients with sickle cell anemia. The creatinine-indexed urinary activity level (units of enzyme activity/milligrams creatinine) and the fractional enzyme excretion (FEE) value, which is defined as the ratio of enzyme clearance to creatinine clearance, were determined for each of the five lysosomal enzymes and compared between the two groups. The mean FEE values for beta-glucuronidase and alpha-galactosidase in the sickle cell patients were 10- and 3.5-fold lower, respectively, than the corresponding control values, and these differences were statistically significant (p < .03) for both enzymes; however, beta-hexosaminidase, beta-galactosidase, and alpha-mannosidase levels in urine were not different between the two groups. When indexed to creatinine, a comparison of the urinary enzyme levels of control and sickle cell patients showed significant differences for beta-glucuronidase (p < .01) and alpha-galactosidase (p < .05) but not for the other three enzymes. Differences in level of plasma enzyme activity between control and sickle cell patients were not significant, except for alpha-galactosidase (p < .05), which was increased slightly (25%) in the sickle cell group. These data indicate that there may be abnormalities in the metabolism of lysosomal enzymes in the kidneys of patients with sickle cell anemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated urinary levels of thromboxane and prostacyclin metabolities in sickle cell disease reflects activated platelets in the circulation

There is evidence for increased factor VII turnover and the associated increased thrombin generation and fibrinolytic activities in sickle cell disease (SCD) that may affect in vivo platelet and endothelial cell reactivity. We studied the release of specific eicosanoids that are indicative of in vivo platelet activation and endothelial cell injury. The circulating and urinary levels of 2,3-dinor thromboxane B2(2,3-dinor-TxB2),TxB2,PGI2 [as 6-keto-PGF1 alpha], and PGE2 were measured in 15HbSS patients, eight HbAA non-haemolytic anaemic individuals and 12 healthy HbAA controls using specific RIAs. The mean urinary 2,3-dinor-TxB2 in the HbSS patients was significantly higher than in both the healthy HbAA and the anaemic controls. 6-keto-PGF1 alpha was undetected in the urines of the healthy HbAA controls, but was measured insignificant amounts in the HbSS and the HbAA anaemic patients. The urinary concentrations of PGE2 and TxB2 in HbSS patients' samples were also significantly higher than those of both control groups (P < 0.05). PGE2 and TxB2 levels were below the detection limit in the plasmas of the HbAA subjects, but were measurable in the HbSS and HbAA anaemic plasmas. The plasma level of 6-keto-PGF1 alpha in the HbSS patients was also significantly higher than in the control groups. The data indicates a persistent inflammatory process in the HbSS patients, and is consistent with the hypothesis that there is platelet and endothelial cell activation in SCD.

Plasma and urinary leukotrienes in sickle cell disease: possible role in the inflammatory process

Sickle cell (HbSS) disease is associated with rheological and inflammatory stresses within the microcirculation. In order to determine the role of leukotrienes in the inflammatory processes in HbSS patients, we analysed plasma and urine levels of leukotrienes (LT); LTB4, LTC4, LTD4, and LTE4 as indicators of their in vivo metabolism. Plasma and urine level samples of 15 HbSS patients in steady-state and age-matched healthy, homozygous (HbAA) controls were extracted for leukotrienes and quantitated by HPLC. Control plasma level of leukotrienes (mean +/- SEM, ng ml-1) were: LTB4, 8.95 +/- 0.26; LTC4, 7.24 +/- 0.21; LTD4, 11.42 +/- 0.40; and LTE4, 14.51 +/- 0.50. Corresponding values for HbSS patients were: LTB4, 6.15 +/- 0.42; LTC4, 13.61 +/- 1.45; LTD4, 6.44 +/- 0.51 and LTE4, 4.97 +/- 0.37. The differences were significant at P < 0.05. Urine levels (mean +/- SEM, ng mmol-1 creatinine), for controls were: LTB4, 10.60 +/- 0.35; LTC4, 360.0 +/- 9.82. Values for HbSS urine were: LTB4, 27.50 +/- 3.33; LTC4, 356.0 +/- 17.87; LTD4, 69.90 +/- 14.51. LTD4 was not detected in control urine. These results suggest that sickle cell patients may exhibit impaired ability to catabolize LTC4 in plasma during steady state conditions. This altered metabolism may contribute to the persistent stress of the microcirculation, and is probably related to the abnormal microvascular rheology of sickle blood cells.

Increased in vivo production of thromboxane in patients with sickle cell disease is accompanied by an impairment of platelet functions to the thromboxane A2 agonist U46619

Thrombosis represents an important cause of mortality in patients with sickle cell disease, in addition to the complications caused by the primary defect of inherited abnormal hemoglobin. To study the involvement of platelets in these complications, we assessed the biosynthesis of thromboxane A2 in samples from 49 patients with sickle cell disease and in 33 control subjects. The urinary excretion of the major arachidonic acid metabolite of platelet origin (11-dehydro-thromboxane B2) and of the vascular endothelial cell (2,3-dinor-6-ketoprostaglandin F1 alpha) were very significantly increased (p < 0.0002) in the patients. In a small group of patients (n = 14), we further investigated the ex vivo response of their platelets to U46619, a stable analogue of thromboxane A2. We observed decreased aggregation and [14C]serotonin release compared with control (p < 0.05); similarly, we found impaired p47 protein phosphorylation (p < 0.05). In contrast, platelets from these patients responded normally to thrombin (0.1 unit/mL). In vivo desensitization of platelets from these patients to thromboxane may constitute a form of regulation that may prevent the propagation of aggregation by this potent inducer, as has been hypothesized in in vitro studies. Our results may also provide a rationale for using antiplatelet drugs in the prophylaxis of thrombotic complications in sickle cell patients.

Urinary magnesium excretion in steady-state sickle cell anaemia

Previous reports indicate that individuals with sickle cell anaemia may be magnesium deficient. The role of renal excretion of magnesium in the pathogenesis of this low magnesium status was investigated in 25 patients with sickle cell anaemia (sicklers) in the steady state and in 25 age- and sex-matched controls with haemoglobin genotype AA. The clearance, excretion fraction and excretion rates of magnesium were enhanced in the sicklers. These patients also had significantly lower erythrocyte and plasma magnesium concentrations than the controls. However expressed, urinary magnesium showed a significant positive correlation with plasma magnesium and a weak negative correlation with erythrocyte magnesium. Furthermore, a significant negative correlation was observed between erythrocyte and plasma magnesium in the sicklers. These results suggest that urinary disposal of magnesium in rates and amounts inappropriate to the body stores of the cation may be one of the mechanisms accounting for hypomagnesaemia and low erythrocyte magnesium content in patients with sickle cell anaemia.

Maintenance of normouricaemia during adolescence in sickle-cell anaemia

Aspects of uric acid metabolism were investigated during adolescence in 122 patients with sickle-cell anaemia in the steady state and 52 matched controls with normal haemoglobin AA. Plasma urate concentrations were significantly lower (P less than 0.02) in male patients than in male controls. No significant differences were observed between either female patients and female controls or total patient group and total control group. Further study in subgroups of the subjects showed that all indices of urinary urate excretion in male patients were significantly increased over male controls or female patients. The increases in these indices in female patients over female controls were not statistically significant. Significant inverse correlations were also found between plasma urate and either renal urate clearance (r = -0.483, P less than 0.02) or fractional urate excretion (r = -0.398, P less than 0.05) in the patients. These findings indicate that patients with sickle-cell anaemia maintain normouricaemia during adolescence by increasing renal urate disposal. This process appears to be more efficient in the male patients.

Urea kinetics: comparison of oral and intravenous dose regimens

Urea kinetics were measured on two separate occasions in five adults with normal haemoglobin genotype (HbAA) and in four who were homozygous for sickle cell disease (HbSS). Prime/intermittent doses of [15N15N]urea were given orally on one occasion and intravenously on the other. In three of the nine individuals there appeared to be significant hydrolysis of the oral dose of urea before absorption, leading to spurious results for the urea kinetics. When only the studies in which isotope was given intravenously were considered, there was a difference in the rate at which urea-N was salvaged, with more urea-N being salvaged by HbSS subjects than HbAA. It is concluded that the oral presentation of isotope can be used to measure urea kinetics provided care is taken to exclude those subjects who are likely to display upper intestinal hydrolysis, and that there are differences in aspects of urea kinetics between HbAA and HbSS which may be of metabolic importance.

Renal involvement in sickle cell-beta thalassemia

Renal function studies were performed in 41 patients with sickle cell-beta thalassaemia (S/b thal) and compared to 14 normal controls and 8 sickle cell (SS) patients. Polyuria, hyposthenuria and mild proteinuria were common in both S/b thal and SS patients. A renal concentrating defect was manifest in all patients studied, and in 4 of the 7 S/b that patients tested, an abnormal acidification test was found. A statistically significant negative correlation (n = 19, r = -0.48, p less than 0.05) was noted between creatinine clearance (CCr) and age for the patients over 30 years. There was no correlation between hemoglobin and CCr; on the contrary, a statistically significant negative correlation was found between CCr and hemoglobin F (n = 29, r = -0.428, p less than 0.05) Our S/b thal and SS patients showed a decreased daily excretion of sodium, calcium, phosphate and magnesium and lower serum magnesium levels than the controls. One third of the S/b thal patients showed hyperuricosuria, and a statistically significant negative correlation was noted between serum uric acid and its fractional excretion in all S/b thal patients (n = 41, r = -0.450, p less than 0.01). Serum phosphate levels were independent of age. A statistically significant positive correlation was found between the tubular reabsorptive capacity for phosphate and the number of painful crises per year (n = 33, r = 0.836, p less than 0.001). We conclude that renal involvement in the double heterozygous state is as severe as in homozygous sickle cell disease.

Usefulness of empiric chest radiography and urinalysis testing in adults with acute sickle cell pain crisis

STUDY OBJECTIVE

To determine the usefulness of obtaining routine chest radiographs and urinalyses on adults presenting to the emergency department in acute sickle cell pain crisis. The hypothesis tested is that in some adult sickle cell patients, sickle cell pain crises are precipitated or accompanied by acute infection that may be clinically occult and that routine screening for pulmonary or urinary tract infection would identify some of these precipitating illnesses.

DESIGN

Prospective clinical study.

SETTING

A university hospital ED.

PATIENTS

All patients more than 14 years old with S-S, S-C, or S-beta-thalassemia sickle hemoglobinopathies who presented to the ED with acute nontraumatic painful complaints during a six-month period.

INTERVENTIONS

All patients underwent posteroanterior and lateral chest radiography, routine urinalysis, and CBC count with reticulocyte count. A standard questionnaire for localizing symptoms of systemic, pulmonary, and urinary tract infection was completed for each patient. Urine cultures were ordered on all patients with voiding symptoms, flank pain, and/or more than 5 WBCs or RBCs per high-power field on urinalysis. Physical examination for evidence of pulmonary and urinary tract infection was carefully performed and recorded for subsequent analysis.

RESULTS

Seventy-one patients with 134 ED presentations were studied over a six-month period. Eight diagnoses of acute pneumonia were made. Four of these patients complained of chest pain (50% vs 48% overall) and three had shortness of breath (38% vs 21%). None of these patients complained of fever or symptoms of upper respiratory illness. Ten diagnoses of urinary tract infection were made. Four of these patients complained of dysuria and frequency; three complained of flank pain. Eleven of the 18 infections (61.1%) did not have a typical history for or suggestive physical or laboratory findings of bacterial infection.

CONCLUSION

In sickle cell disease patients with pain crisis, routine chest radiography and urinalysis may be clinically useful and cost effective in the early diagnosis of crisis-related infection.

Determinants of nocturnal enuresis in homozygous sickle cell disease

The determinants of nocturnal enuresis in homozygous sickle cell (SS) disease have been investigated in 16 enuretic and 16 age and sex matched non-enuretic children. Overnight fluid deprivation tests (8pm-8am) demonstrated no significant difference in maximum urine osmolality or urine volumes, although the latter tended to be higher in the enuretic children. Maximum functional bladder capacity, estimated by maximum voided volume during oral fluid loading, was lower and the ratio of overnight urine volume to maximum functional bladder capacity higher in the enuretic than the non-enuretic group. Enuretic children were more likely than non-enuretics to be considered deep sleepers by their family. High urine volumes may contribute to nocturnal enuresis in SS disease, although the similar values in enuretic and non-enuretic children implies that additional factors determine the presence of enuresis. Low maximum functional bladder capacity, and a high ratio of overnight urine volume to maximum functional bladder capacity, appear to be important determinants.

Proteinuria in sickle cell trait and disease: an electrophoretic analysis

Using ultrafiltration and SDS-PAGE, abnormal urinary protein excretion was found in 25.4% of 189 persons with sickle cell disease and trait, but none of 72 controls. Based upon molecular weight of urinary proteins, underlying renal lesions were classified as glomerular, tubular, or both. Altered protein excretion appeared at an early age, was more abnormal in older subjects, and was related to the severity of sickle cell disease (SS greater than SC = S/beta Thal greater than AS). Since none of the subjects had yet developed clinically significant renal disease, SDS-PAGE may permit early detection of patients who require careful follow-up or aggressive therapy.

Altered vascular reactivity in sickle hemoglobinopathy. A possible protective factor from hypertension

Patients with sickle cell anemia have considerably less hypertension than the black population in general. Factor(s) offering "protection" from hypertension in these patients remain unknown. Hormonal and hemodynamic parameters involved in blood pressure regulation were evaluated in normotensive, stable sickle cell patients and black nonsickle normotensive controls. There was no difference in systolic, diastolic, or mean arterial blood pressure between the two groups. The characteristic hemodynamic findings of increased cardiac index, renal plasma flow, and plasma volume were observed in the sickle cell patients. Urinary sodium excretion was comparable on an ad libitum, high sodium, and low sodium diet. In contrast, plasma renin activity was greater in sickle cell patients at all levels of sodium intake in both supine and upright positions. These findings suggested possible altered vascular responsiveness to endogenous angiotensin II. Plethysmography revealed that sickle cell patients had greater forearm blood flow than normal controls and black nonsickle chronic anemic controls at rest, during cold stimulation, and during exercise. Forearm vascular resistance was significantly lower in the patients and did not increase with cold-induced, sympathetic-mediated stimulation. To assess these findings more directly, the pressor response to the exogenous administration of graded doses of angiotensin II and norepinephrine was measured. There was a marked decrease in the pressor response to angiotensin II but not to norepinephrine in the sickle cell patients. The findings in these studies indicate fundamental differences in blood pressure control in the sickle cell patient, probably at the vascular level.

Zinc status in children and young adults with sickle cell disease

Previous studies have suggested an association of zinc deficiency and short stature in some children and adults with sickle cell disease (SCD). As a result, zinc supplementation has been recommended for these patients. The mechanism for zinc deficiency in certain patients with SCD is unknown, although renal loss of zinc has been suggested as a contributing factor. The zinc status of 29 subjects with SCD and 18 black controls was studied. No evidence of zinc deficiency in our population with SCD was found when plasma and cellular zinc levels were measured. Likewise, levels of two zinc-dependent enzymes, alkaline phosphatase and delta-aminolevulinic acid dehydratase, were normal in these subjects with SCD. Although adolescent subjects with SCD tended to be shorter than control subjects, there was no correlation between the height-forage z score and plasma zinc levels (r = -.31). It was concluded that zinc deficiency was not present in our population with SCD, and that there was no correlation between plasma zinc levels and the height-for-age z score in growing adolescent patients with SCD. These findings suggested that zinc supplementation may not be necessary in all patients with SCD.