Net renal tubular reabsorption of zinc in healthy man and impaired handling in sickle cell anemia

Zinc, Magnesium, and Copper Levels in Patients with Sickle Cell Disease: A Systematic Review and Meta-analysis

Background  Sickle cell disease (SCD) is associated with oxidative stress due to an imbalance between production and elimination of the reactive oxygen species. It has been reported that SCD patients are at risk of multiple micronutrients' deficiencies, including several trace elements involved in the antioxidation mechanisms. We aimed to assess the status of these micronutrients in SCD patients.

Methods  This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The databases of MedLine, Embase, and PsycInfo were used for the systematic search from time the databases existed until April 2021. A total of 36 studies fulfilled the eligibility criteria. We calculated the pooled standardized mean difference (SMD) of serum zinc, magnesium, or copper levels among patients with SCD and their healthy controls.

Results  SCD patients had significantly lower zinc (SMD = −1.27 [95% CI: 1.67−0.87, p 0.001]) and magnesium levels (SMD = −0.53 [95% CI: 1.0−0.06, p 0.026] than their controls. Copper level was found to be significantly higher in SCD patients, with SMD = 0.68 (95% CI: 0.05−1.32, p 0.004).

Conclusion  This review showed that SCD patients may potentially prompt to have lower zinc and magnesium levels and higher copper levels compared with those without the disease. Future research need to be directed to investigate clinical outcome of nutritional difficiencies in patients with SCD, as well as the possibility of implementing nutritional supplement programs which may help minimizing the harmful effects of the disease on human body.

Zinc as a Drug for Wilson's Disease, Non-Alcoholic Liver Disease and COVID-19-Related Liver Injury

Zinc is the second most abundant trace element in the human body, and it plays a fundamental role in human physiology, being an integral component of hundreds of enzymes and transcription factors. The discovery that zinc atoms may compete with copper for their absorption in the gastrointestinal tract let to introduce zinc in the therapy of Wilson's disease, a congenital disorder of copper metabolism characterized by a systemic copper storage. Nowadays, zinc salts are considered one of the best therapeutic approach in patients affected by Wilson's disease. On the basis of the similarities, at histological level, between Wilson's disease and non-alcoholic liver disease, zinc has been successfully introduced in the therapy of non-alcoholic liver disease, with positive effects both on insulin resistance and oxidative stress. Recently, zinc deficiency has been indicated as a possible factor responsible for the susceptibility of elderly patients to undergo infection by SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic. Here, we present the data correlating zinc deficiency with the insurgence and progression of Covid-19 with low zinc levels associated with severe disease states. Finally, the relevance of zinc supplementation in aged people at risk for SARS-CoV-2 is underlined, with the aim that the zinc-based drug, classically used in the treatment of copper overload, might be recorded as one of the tools reducing the mortality of COVID-19, particularly in elderly people.

Pica in Pediatric Sickle Cell Disease

Pica is the developmentally inappropriate consumption of non-nutritive items for at least one month. Pica can lead to many adverse outcomes, but the exact pathophysiology of pica is unknown or variable across populations. Several studies have evidenced that there is a high prevalence of pica among youth with sickle cell disease (SCD). However, the lack of knowledge regarding the correlates of pica contributes to overlooking the condition, inaccurate diagnoses, and a lack of evidence-based treatments once pica is identified. This review examines the literature to develop a biopsychosocial model of pica in SCD. Elucidating the potential relationships among the proposed biological, psychological, and social factors, and pica will inform our understanding of this phenomenon in pediatric SCD and may guide future research and clinical recommendations.

Sickle Hepatopathy

Sickle hepatopathy is an umbrella term describing various pattern of liver injury seen in patients with sickle cell disease. The disease is not uncommon in India; in terms of prevalence, India is second only to Sub-Saharan Africa where sickle cell disease is most prevalent. Hepatic involvement in sickle cell disease is not uncommon. Liver disease may result from viral hepatitis and iron overload due to multiple transfusions of blood products or due to disease activity causing varying changes in vasculature. The clinical spectrum of disease ranges from ischemic injury due to sickling of red blood cells in hepatic sinusoids, pigment gall stones, and acute/chronic sequestration syndromes. The sequestration syndromes are usually episodic and self-limiting requiring conservative management such as antibiotics and intravenous fluids or packed red cell transfusions. However, rarely these episodes may present with coagulopathy and encephalopathy like acute liver failure, which are life-threatening, requiring exchange transfusions or even liver transplantation. However, evidence for their benefits, optimal indications, and threshold to start exchange transfusion is limited. Similarly, there is paucity of the literature regarding the end point of exchange transfusion in this scenario. Liver transplantation may also be beneficial in end-stage liver disease. Hydroxyurea, the antitumor agent, which is popularly used to prevent life-threatening complications such as acute chest syndrome or stroke in these patients, has been used only sparingly in hepatic sequestrations. The purpose of this review is to provide insights into epidemiology of sickle cell disease in India and pathogenesis and classification of hepatobiliary involvement in sickle cell disease. Finally, various management options including exchange transfusion, liver transplantation, and hydroxyurea in hepatic sequestration syndromes will be discussed in brief.

Selenium Status and Hemolysis in Sickle Cell Disease Patients

Sickle cell disease (SCD) is a genetic hemoglobinopathy characterized by chronic hemolysis. Chronic hemolysis is promoted by increased oxidative stress. Our hypothesis was that some antioxidant micronutrients (retinol, tocopherol, selenium, and zinc) would be determinant factors of the degree of hemolysis in SCD patients. We aimed to investigate the nutritional adequacy of these antioxidants and their relationships to hemolysis. The study included 51 adult SCD patients regularly assisted in two reference centers for hematology in the State of Rio de Janeiro, Brazil. Serum concentrations of retinol, alpha-tocopherol, selenium, and zinc were determined by high-performance liquid chromatography or atomic absorption spectrometry. Hematological parameters (complete blood count, reticulocyte count, hemoglobin, direct and indirect bilirubin, total bilirubin, lactate dehydrogenase) and inflammation markers (leukocytes and ultra-sensitive C-reactive protein) were analyzed. A linear regression model was used to test the associations between the variables. Most patients presented selenium deficiency and low selenium consumption. Linear regression analysis showed that selenium is the main determinant of hemolysis among the antioxidant nutrients analyzed. Thus, data from this study suggest that the nutritional care protocols for patients with SCD should include dietary sources of selenium in order to reduce the risk of hemolysis.

Zinc for Infection Prevention in Sickle Cell Anemia (ZIPS): study protocol for a randomized placebo-controlled trial in Ugandan children with sickle cell anemia

BACKGROUND

Sickle cell anemia (SCA) is the most common inherited hemoglobinopathy worldwide. Infection is a major cause of illness and death in children with SCA, especially in sub-Saharan Africa where an estimated 50-90% of affected children die before their fifth birthday. Interventions to reduce the incidence and severity of infections are needed urgently. A high proportion of adults and children with SCA are zinc-deficient, and zinc deficiency leads to impaired immunity and an increased risk of infection. Zinc supplementation has been shown to decrease the risk of infection in adolescents and adults, but there are no data on the effectiveness of zinc for prevention of infection in children < 5 years of age with SCA.

METHODS/DESIGN

The study will be a randomized, placebo-controlled, double-blind clinical trial in which 250 Ugandan children 1.00-4.99 years of age with SCA will receive daily zinc supplementation (10 mg oral dispersible tablet) or identical placebo for 12 months.

DISCUSSION

If this trial shows a reduction in severe or invasive infection incidence, it would be the basis for a multi-site, multi-country clinical trial to assess real-world safety and efficacy of zinc in African children with SCA. Since zinc is safe, inexpensive, and easy to administer, this trial has the potential to improve the health of hundreds of thousands of African children with SCA through reduction of infection-related morbidity and mortality.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03528434. Registered on May 17, 2018 Protocol Version: 1.0. Date: Dec 11, 2017 Sponsor: Indiana University. Sponsor's protocol identifier, 1712339562.

Dynamic homeostasis modeling of Zn isotope ratios in the human body

Recent research performed on volunteers and patients suggested that diet, health, and basal metabolic rates (BMR) are factors controlling the bodily Zn isotope compositions (isotopic homeostasis).

Acute kidney injury following acute liver failure: potential role of systemic cadmium mobilization?

OBJECTIVE

A significant fraction of patients with acute liver failure (ALF) suffer from a concomitant acute kidney injury (AKI), the mechanism of which is probably multifactorial. Cadmium (Cd) is a widespread environmental pollutant and a tubulotoxic metal that accumulates in the liver. We tested the hypothesis that a release of Cd during ALF may cause a redistribution of Cd from the liver to the kidneys and play a role in the occurrence of ALF-associated AKI.

METHODS

Twenty patients with ALF (ALF-patients), 20 patients from the ICU with no liver damage at admission (ICU-controls) and 20 healthy controls were recruited to compare the 24-h urinary excretion rate of Cd with that of lead (Pb), a nephrotoxic metal that does not accumulate in the liver, and zinc (Zn), a non-nephrotoxic element found in high amounts in the liver. The excretion rates of the low-molecular-weight proteins (LMWPs) were monitored.

RESULTS

ALF-patients excreted markedly more Cd than the healthy controls and ICU-controls. In ALF-patients, the four urinary LMWPs (RBP, β2-MG, CC16 and α1-MG) increased as a function of Cd excretion, with high correlation coefficients. The prevalence of patients excreting a high amount of LMWPs also increased with increasing Cd excretion. No relationship was found between the other elements investigated and the LMWPs, with the exception of copper, which shares close toxicokinetic similarities with Cd.

CONCLUSIONS

This study shows a strong association between urinary Cd levels and the excretion rates of LMWPs in patients with ALF. A causal relationship is possible but could not be fully demonstrated in this study.

Gastrointestinal and hepatic complications of sickle cell disease

Sickle cell disease (SCD) is an autosomal recessive abnormality of the beta-globin chain of hemoglobin (Hb), resulting in poorly deformable sickled cells that cause microvascular occlusion and hemolytic anemia. The spleen is almost always affected by SCD, with microinfarcts within the first 36 months of life resulting in splenic atrophy. Acute liver disorders causing right-sided abdominal pain include acute vaso-occlusive crisis, liver infarction, and acute hepatic crisis. Chronic liver disease might be due to hemosiderosis and hepatitis and possibly to SCD itself if small, clinically silent microvascular occlusions occur chronically. Black pigment gallstones caused by elevated bilirubin excretion are common. Their small size permits them to travel into the common bile duct but cause only low-grade obstruction, so hyperbilirubinemia rather than bile duct dilatation is typical. Whether cholecystectomy should be done in asymptomatic individuals is controversial. The most common laboratory abnormality is an elevation of unconjugated bilirubin level. Bilirubin and lactate dehydrogenase levels correlate with one another, suggesting that chronic hemolysis and ineffective erythropoiesis, rather than liver disease, are the sources of hyperbilirubinemia. Abdominal pain is very common in SCD and is usually due to sickling, which resolves with supportive care. Computed tomography scans might be ordered for severe or unremitting pain. The liver typically shows sickled erythrocytes and Kupffer cell enlargement acutely and hemosiderosis chronically. The safety of liver biopsies has been questioned, particularly during acute sickling crisis. Treatments include blood transfusions, exchange transfusions, iron-chelating agents, hydroxyurea, and allogeneic stem-cell transplantation.

Zinc supplementation decreases oxidative stress, incidence of infection, and generation of inflammatory cytokines in sickle cell disease patients

Zinc deficiency is common in adult sickle-cell disease (SCD) patients. We previously demonstrated that zinc supplementation to adult SCD patients decreased the incidences of infections and hospital admissions. We hypothesize that zinc supplementation improves T-helper cell function and decreases vascular endothelial cell activation, oxidative stress, and nuclear factor-kappa B (NF-kappaB)-DNA binding in mononuclear cells (MNCs) in SCD patients. To test this hypothesis, 36 SCD patients were recruited and randomly divided into 2 groups. One group (n = 18) received 25-mg zinc orally thrice a day for 3 months. The other group (n = 18) received placebo. The results indicate that the zinc-supplemented group had decreased incidence of infections compared with the placebo group. After zinc supplementation, red blood cell, hemoglobin (Hb), hematocrit, (Hct), plasma zinc, and antioxidant power increased; plasma nitrite and nitrate (NOx), lipid peroxidation products, DNA oxidation products, and soluble vascular cell adhesion molecule-1 decreased in the zinc-supplemented group, compared with the placebo group. Zinc-supplemented patients exhibited significant decreases in lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-alpha) and IL-1beta mRNAs, and TNF-induced nuclear factor of kappaB-DNA binding in MNCs, compared with the placebo group. Ex vivo addition of zinc to MNCs isolated from the placebo subjects decreased TNF-alpha and IL-1beta mRNAs. Zinc supplementation also increased relative levels of IL-2 and IL-2Ralpha mRNAs in phytohemagglutinin-p-stimulated MNCs. These results suggest that zinc supplementation may be beneficial to SCD patients.

Study of zinc and growth hormone in sickle cell disease

About 25% of children with sickle cell disease (SCD) have statural deficit and retarded skeletal maturation and pubertal development. These disorders have been attributed to low serum concentrations of zinc. We report the study of serum zinc in 34 patients with SCD, of whom 17 had statural deficit (SCS group) and 17 without growth deficiency (SCN group). They were compared with 20 normal children (N group). GH secretion and thyroid function were investigated in the group with short stature (SCS) in order to rule out GH deficiency and hypothyroidism. The mean serum zinc concentration was 108.45+/-22.888 microg/100 ml in the N group, 87.529+/-30.069 microg/100 ml in the SCN group and 82.765+/-34.766 microg/100 ml in the SCS group. There was a statistically significant difference between the mean of the N group and the mean of the SCN group (p<0.05) but no difference was found between the two groups of patients (N>SCN=SCS). Although there is a well-established zinc deficiency in patients with SCD, the statural retardation found in the SCS group could not be attributed only to zinc deficiency. Many other severe metabolic disturbances are also involved.

Zinc and the immune system

Zn is an essential trace element for all organisms. In human subjects body growth and development is strictly dependent on Zn. The nervous, reproductive and immune systems are particularly influenced by Zn deficiency, as well as by increased levels of Zn. The relationship between Zn and the immune system is complex, since there are four different types of influence associated with Zn. (1) The dietary intake and the resorption of Zn depends on the composition of the diet and also on age and disease status. (2) Zn is a cofactor in more than 300 enzymes influencing various organ functions having a secondary effect on the immune system. (3) Direct effects of Zn on the production, maturation and function of leucocytes. (4) Zn influences the function of immunostimulants used in the experimental systems. Here we summarize all four types of influence on the immune function. Nutritional aspects of Zn, the physiology of Zn, the influence of Zn on enzymes and cellular functions, direct effects of Zn on leucocytes at the cellular and molecular level, Zn-altered function of immunostimulants and the therapeutic use of Zn will be discussed in detail.

Effects of zinc deficiency on Th1 and Th2 cytokine shifts

Nutritional deficiency of zinc is widespread throughout developing countries, and zinc-deficient persons have increased susceptibility to a variety of pathogens. Zinc deficiency in an experimental human model caused an imbalance between Th1 and Th2 functions. Production of interferon-gamma and interleukin (IL)-2 (products of Th1) were decreased, whereas production of IL-4, IL-6, and IL-10 (products of Th2) were not affected during zinc deficiency. Zinc deficiency decreased natural killer cell lytic activity and percentage of precursors of cytolytic T cells. In HuT-78, a Th0 cell line, zinc deficiency decreased gene expression of thymidine kinase, delayed cell cycle, and decreased cell growth. Gene expression of IL-2 and IL-2 receptors (both alpha and beta) and binding of NF-kappaB to DNA were decreased by zinc deficiency in HuT-78. Decreased production of IL-2 in zinc deficiency may be due to decreased activation of NF-kappaB and subsequent decreased gene expression of IL-2 and IL-2 receptors.

Effect of zinc supplementation on incidence of infections and hospital admissions in sickle cell disease (SCD)

Zinc deficiency is a common nutritional problem in adult sickle-cell disease (SCD) patients. Hyperzincuria and increased requirement of zinc due to continued hemolysis in SCD are probable bases for zinc deficiency in these patients. Zinc deficiency affects adversely T-helper1 (TH1) functions and cell mediated immunity and interleukin (IL)-2 production is decreased in zinc deficient subjects. We hypothesized that zinc supplementation will improve T-helper1 function and decrease incidence of infections in patients with SCD. We tested this hypothesis in 32 SCD subjects who were divided in three groups (Grs A, B, and C). Grs A (n = 11) and B (n = 10) were zinc deficient based on cellular zinc criteria and Gr C (n = 11) were zinc sufficient. Gr A subjects were observed for 1 year (baseline), following which they received zinc acetate (50 to 75 mg of elemental zinc orally daily) for 3 years. Gr B subjects were observed for 1 year (baseline), following which they received placebo for 1 year and then switched to zinc supplementation (50 to 75 mg of elemental zinc orally daily) for 2 years. Gr C subjects did not receive any intervention inasmuch as they were zinc sufficient. Prolonged zinc supplementation resulted in an increase in lymphocyte and granulocyte zinc (P = 0.0001), and an increase in interleukin-2 production (P = 0.0001), decreased incidence of documented bacteriologically positive infections (P = 0.0026), decreased number of hospitalizations and decreased number of vaso-occlusive pain crisis (P = 0.0001). The predominant pathogens isolated were staphylococci and streptococci involving the respiratory tract and aerobic gram-negative bacteria, particularly Escherichia coli, involving the urinary tract. Further confirmation of our observations will require prospective studies of zinc supplementation in a larger number of SCD patients.

Zinc status relates to hematological deficits in middle-aged women

OBJECTIVE

The objective of our study was to investigate zinc (Zn) status and the effects of Zn supplementation in relation to iron deficiency anemia in middle-aged women. It is important to define the role of Zn in hematologic abnormalities and to determine the frequency of Zn deficiency.

METHODS

Fifty-two Japanese women, selected from a health examination survey on 6200 women, had hemoglobin concentrations below 12.0 g/dl, total iron binding capacity (TIBC) below 390 micrograms/dl and fairly normocytemia. These 52 were divided into three groups and we then compared the hematological status before and after iron (group A) or Zn (group B) or iron plus Zn (group C) supplementation.

RESULTS

After treatment, concentrations of hemoglobin (Hb) increased slightly in groups A and B, but not statistically significant. In group C, Hb levels were significantly increased from 10.8 +/- 1.1 to 12.8 +/- 1.1 g/dl. Furthermore, numbers of RBC and reticulocytes, and concentrations of albumin were also increased significantly. Increased values over 1.0 g/dl of hemoglobin levels were noted in four women (26.6%) in group A, three women (14.2%) in group B and 13 women (81.2%) in group C.

CONCLUSION

Zn status to some extent can account for hematological abnormalities in middle-aged women. At least 5.0% of middle-aged Japanese women may have Zn deficiency. Normocytic anemia with low TIBC levels may serve as a good indicator of a marginal Zn deficiency.

Plasma zinc status, growth, and maturation in children with sickle cell disease

OBJECTIVE

The objective of this study was to determine the relation of plasma zinc (Zn) status to growth and maturation in children with SS genotype sickle cell disease.

STUDY DESIGN

A cross-sectional study of 104 subjects who were 50% female and ranged in age from 0.4 to 18 years was performed. Measures included plasma Zn concentration (Znp), height, weight, skinfold thicknesses, elbow breadth, upper arm muscle area, and fat-free mass and fat mass by total body electrical conductivity. Skeletal maturation was assessed by hand-wrist x-ray evaluation and sexual maturation by Tanner stage.

RESULTS

A total of 44% of the patients had low Znp (<10.7 micromol/L [70 microg/dl]); those with low Znp had significantly lower SD scores for height (p = 0.003), weight (p = 0.003), upper arm muscle area (p = 0.045), fat-free mass (p = 0.025), and elbow breadth (p = 0.017) and greater skeletal maturation delay (p = 0.04). In older children (>9 years) low Znp was associated with decreased Tanner scores for pubic hair (p = 0.001) and breast and genital maturation (p = 0.009). No significant differences were seen in age, sex, or fat stores according to Zn status.

CONCLUSIONS

Decreased plasma Zn is common in children with SS genotype sickle cell disease and is associated with decreased linear growth, skeletal growth, muscle mass, and sexual and skeletal maturation.

Increased urinary zinc excretion in cancer patients is linked to immune activation and renal tubular cell dysfunction

Urinary zinc excretion is known to be increased in cancer patients, but the pathogenesis of this phenomenon remains uncertain. Both skeletal muscle catabolism and renal tubular cell dysfunction have been proposed to explain this observation. We have investigated urinary zinc and N-acetyl-beta-D-glucosaminidase (NAG), an indicator of renal tubular cell dysfunction, as well as serum neopterin, an index of systemic immune activation, in 22 patients with cancer and seven controls. Both serum neopterin and urinary zinc were significantly elevated in cancer patients (15.8 +/- 12.7 versus 7.3 +/- 2.3 nmol l-1 and 1.77 +/- 0.80 versus 1.21 +/- 0.41 mmol mol-1 creatinine, P < 0.02 and P < 0.05, respectively), while NAG was similar in cancer patients and the controls (13.58 +/- 13.80 versus 13.68 +/- 12.19 mu kat mol-1 creatinine). A significant correlation was observed between serum neopterin and urine zinc (rs = 0.5119, P < 0.02), serum neopterin and urine NAG (rs = 0.6761, P < 0.002), and urinary zinc and NAG (rs = 0.6348, P < 0.002). In conclusion, the present data indicate a link between urinary zinc excretion and immune activation as well as renal tubular cell dysfunction. In addition, renal tubular cell dysfunction appears to be linked to immune activation.

Association between renal tubular cell dysfunction and increased urinary zinc excretion in cancer patients

Although an increase in renal zinc excretion in cancer patients is well documented, the mechanisms involved are still disputed. As recent studies have raised the question of the role of renal tubular cell dysfunction in the elevation of urinary zinc output, we have examined urinary zinc excretion and the excretion of N-acetyl-beta-D-glucosaminidase (NAG), an indicator of tubular cell dysfunction, in 30 patients with cancer, 28 healthy controls and 20 patients with benign non-inflammatory disorders. As expected, urinary zinc excretion was significantly higher in the cancer patients compared with controls and patients with benign disorders (2.64 +/- 3.05 vs. 0.86 +/- 0.36 and 0.89 +/- 0.29 mmol mol creatinine-1, p < 0.001). NAG activity was also elevated (18.9 +/- 20.1 vs. 4.32 +/- 3.33 and 9.99 +/- 9.72 mukat mol creatinine-1, p < 0.001 and p < 0.05, respectively). A significant correlation between urine zinc and NAG was observed in all three groups (rho = 0.73, p < 0.001, rho = 0.55, p < 0.01 and rho = 0.45, p < 0.05, respectively). In conclusion, our data provide additional support for the role of renal tubular cell dysfunction in hyperzincuria in cancer. Urinary zinc measurement may represent an alternative approach to detecting renal tubular dysfunction in human pathology.

Urinary zinc excretion and acute phase response in cancer patients

We investigated urinary zinc and serum levels of C-reactive protein, alpha-1 acid glycoprotein, haptoglobin, transferrin and prealbumin in 55 patients with solid tumors and 20 controls. Urinary zinc, serum C-reactive protein, alpha-1 acid glycoprotein and haptoglobin were significantly higher, and serum prealbumin was significantly lower in cancer patients. A significant positive correlation between urinary zinc and C-reactive protein, alpha-1 acid glycoprotein and haptoglobin, as well as a negative correlation with transferrin and prealbumin were observed. Hyperzincuria in cancer patients appears to be linked to the acute phase response. Our data provide further evidence implicating systemic inflammatory response in increased urinary zinc excretion.

Urinary zinc excretion in a patient with burns: a caveat when using bladder catheters in urine zinc studies

The results of a longitudinal study on plasma and urine zinc concentrations in a patient with 68 per cent burns are described. Special attention was paid to possible zinc contamination due to the use of bladder catheters for urine sampling. The course of the plasma and urine zinc concentrations during the first 50 days in hospital was comparable to those reported in the literature. It was shown that surgery was associated with a pronounced rise in urine zinc level, while catheter replacement caused no significant increase in urinary zinc content in this particular patient. However, measurements of zinc content of and zinc release from three types of bladder catheters showed that the two types of latex-based catheters contained about 0.25 per cent zinc, versus 0.01 per cent in the siliconelastomer equivalent. During an 8 h perfusion latex catheters released about 1.2 mumols zinc (2.5 mumols/l). Possible errors in urine zinc determinations due to zinc contamination from catheters are calculated. Recommendations are made for minimizing these errors.