Glucose |
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▸ Glycosuria occurs when the filtered load of glucose exceeds the ability of the proximal tubule to reabsorb it, eg, diabetes mellitus, Cushing's syndrome, etc ▸ The threshold for tubular reabsorption can be altered in isolated tubular dysfunction like renal glycosuria or generalised ones like Fanconi syndrome, cystinosis or Wilson’s disease, where blood glucose is normal
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Ketones |
▸ Ketones are products of fat metabolism not normally found in urine ▸ Among the ketones, only acetoacetic acid and acetone that react with nitroprusside are detected by dipsticks
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▸ Positive in diabetes mellitus, pregnancy, ketogenic diet ▸ In hypoglycaemia, presence of ketones suggests ketotic hypoglycaemia, if absent, points to fatty acid metabolic abnormalities like medium chain acyl CoA dehydrogenase deficiency ▸ Ketonuria is a physiological response to starvation; many small children get morning ketonuria with normal ‘starvation’ overnight ▸ Ketonuria also occurs with cold exposure and extended periods of exercise
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pH range 4.5–8 |
▸ Generally, patients on a typical western diet tend to have slightly lower acidic urinary pH ▸ For accurate measurement of pH, urine sample should be sealed to prevent CO2 evaporation ▸ Delaying the test >30 min at room temperature makes urine alkaline due to the breakdown of urea |
▸ Mundane clinical conditions like diarrhoea and vomiting that result in dehydration are the common causes of acidic urine ▸ Interestingly in conditions like pyloric stenosis with metabolic alkalosis, urine is paradoxically acidic due to the preferential excretion of hydrogen ions to conserve potassium in the blood ▸ Urine pH can help to determine the cause of metabolic acidosis (pH>5 indicates renal tubular acidosis rather than an inborn error of metabolism) and distinguish different types of renal tubular acidosis3 ▸ Alkaline urine in patient with urinary tract infection suggests urea splitting organism like Proteus, which can cause magnesium–ammonium phosphate crystals, which form staghorn calculi3 ▸ Alkaline urine can also form calcium carbonate and calcium phosphate stones ▸ Acidic urine is associated with uric acid stones ▸ Urine pH is actively monitored in therapeutic alkalisation for conditions like salicylate poisoning and tumour lysis syndrome
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SG Normal range 1.003–1.030 |
▸ SG test is based on the change of pH dye due to binding H+ ions, which in turn linearly corresponds to urine osmolality ▸ Hence physiologically SG test reflects hydration status and concentrating ability of the kidney ▸ <1.010 indicates relative hydration ▸ >1.020 indicates relative dehydration ▸ SG is high in urine with significant proteinuria ▸ As SG test is closely related to H+ ion concentration it can be falsely elevated at urine pH <6 and falsely lowered by urine pH >7 ▸ Poor correlation with pathological urine to estimate urine osmolality4
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▸ Increased with glycosuria, proteinuria, syndrome of inappropriate antidiuretic hormone secretion4 ▸ Decreased with diuretics, diabetes insipidus, adrenal insufficiency, aldosteronism and impaired tubular function ▸ Low SG in a dehydrated patient indicates impaired concentrating ability, which points towards a renal tubular dysfunction
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Bilirubin |
▸ Bilirubin is not normally detected in the urine ▸ Even a trace of bilirubin in the urine requires further investigations ▸ Bilirubin is destroyed by light and air, hence should be tested promptly or stored properly |
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Urobilinogen |
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