Baseline Serum and Urine Osmolality and Factors that affect it in Steady State Sickle Cell Disease Patients

Abstract

It is over a century since the discovery of Sickle Cell Disease (SCD) and since then, a lot more is still being discovered about the pathophysiology of the disease. Notable amongst the various factors that affect the disease’s pathophysiology and management is red cell dehydration. Factors that affect cellular dehydration and serum osmolality in SCD patients are not very clearly understood. An objective method among of assessing SCD patient’s hydration status is by measuring the serum and urine osmolality. Limited data exist on factors that affect the hydration status of sickle-cell disease patients especially in Ghana and sub-Saharan Africa. There is therefore the need to collate data about these factors to help in the management of SCD. Aim: The aim of this study was to determine factors that affect serum and urine osmolality in steady-state HbSS and HbSC SCD patients. Methodology: This was a Case-Control study that was conducted at the Department of Haematology (Sickle Cell Clinic), Korle-Bu Teaching Hospital (KBTH) in Accra. 120 cases of SCD (80 HbSS and 40 HbSC genotype) in their steady-state were matched for age to 60 controls. A structured questionnaire was used to obtain the demographic characteristics of recruited subjects, medical history, physical examination findings, a 24-hour dietary recall and frequency of consumption of sodium-rich food. Five millilitres (mls) of venous blood and 5mls of mid-stream urine samples were obtained from each subject. Serum, urine osmolality, full-blood count, blood urea, electrolytes and creatinine (BUE & Cr) were determined. Urine routine examination (Urine R/E) was also done to assess urine pH and specific gravity. Bivariate analysis was used to compare the variables measured, with a p-value < 0.05 deemed as significant. Results: Compared to the mean serum osmolality of the control group (354.50±82.37)mmol/kg, SCD patients (HbSS and HbSC) had a higher mean serum osmolality (440.87±113.14 and 422.90±88.59)mmol/kg respectively (p-value <0.001). The mean urine osmolality of HbSS and HbSC patients (452.28 ± 109.41 and 498.28±87.26)mmol/kg respectively was significantly lower compared to HbAA individuals (681.23±276.82) mmol/kg (p-value <0.001). Comparing HbSS and HbSC patients, there was no significant difference in the mean serum osmolality (p-value =0.382), but a significant increase in the mean urine osmolality of HbSC patients compared to HbSS patients (p-value =0.020). There was a weak negative correlation between serum osmolality and dietary Sodium (r= -0.192), between serum osmolality and average water intake (r= -0.025), between serum osmolality and dietary Protein (r= -0.098) and between serum osmolality and dietary Potassium (r= -0.052) in SCD patients. Analysing data from the Food Frequency Table, majority (> 50%) of study participants (HbSS, HbSC AND HbAA) did not consume most sodium-rich foods (salted meals) very often. The only salt-rich food assessed that was consumed often was stock cubes. Majority (>60%) of study participants (HbSS, HbSC AND HbAA) obtained their food from Food Vendors making it difficult to accurately quantify their food consumption. Conclusion: Sickle Cell Disease patients have a high serum osmolality and a low urine osmolality. The HbSC patients have a higher urine osmolality compared with HbSS patients. In general, study participants did not frequently consume sodium-rich foods. Serum osmolality decreases with increasing consumption of sodium-rich diets, thus the high serum osmolality and low urine osmolality observed in SCD patients is mainly due to the disease pathophysiology.