An 8-month-old previously healthy infant is brought to the urgent care clinic due to vomiting and watery diarrhea for the past 3 days. He attends a day care where recently several other children had similar symptoms. His mother states that the infant is less active and has no interest in feeding. Physical examination shows a listless infant with tachycardia, dry mucous membranes, and decreased skin turgor. The abdomen is nontender with hyperactive bowel sounds. Compared to pre-illness levels, which of the following sets of laboratory findings are most likely present in this patient?

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This patient's history of vomiting and diarrhea and physical examination findings of tachycardia, dry mucous membranes, and decreased skin turgor are consistent with moderate to severe hypovolemia. Vomiting and diarrhea cause gastrointestinal losses of both sodium and water from the extracellular space with a consequent decrease in plasma volume. Because red blood cells and proteins such as albumin are relatively large and trapped intravascularly, these blood components become concentrated, leading to increased hematocrit and increased serum albumin. Such hemoconcentration can be a clue to hypovolemia caused by salt and/or water depletion; however, it does not occur with hypovolemia due to acute blood loss because red blood cells and albumin are also depleted. In the setting of hypovolemia, the kidneys respond by increasing sodium reabsorption to increase circulating blood volume. This increased sodium reabsorption occurs in both the distal renal tubule via increased aldosterone activity and the proximal renal tubule through poorly understood mechanisms. Uric acid absorption is closely tied and directly related to sodium absorption in the proximal renal tubule; therefore, there is typically increased serum uric acid in the setting of hypovolemia. Although uric acid levels are not typically collected in the management of hypovolemia, the relationship between hypovolemia and serum uric acid level has clinical application in that hypovolemia increases the risk of acute gout flares. Educational objective: Hypovolemia due to loss of sodium and/or water causes increased concentration of red blood cells (ie, hematocrit) and albumin as both of these blood components are trapped within the intravascular space. Hypovolemia also triggers increased absorption of uric acid in the proximal renal tubule, resulting in an increased serum uric acid level. __________ References: Renal transport of uric acid: evolving concepts and uncertainties. (http://www.ncbi.nlm.nih.gov/pubmed/23089270)

An 8-Month-Old Previously Healthy Infant Is Brought to the Urgent