A 33-year-old woman presents to the primary care physician for a month-long history of palpations and diarrhea. She has no known medical history. She denies taking any prescribed medication and has not traveled anywhere recently; however, she reports being exposed to “lots of sick people” as part of her job as a nurse. On physical examination, she appears anxious, but the rest of her examination results, including vital signs, are within normal limits. Her BMI is 21 kg/m2 . Laboratory studies are as follows:
Which of the following is the MOST likely cause for her laboratory abnormalities?
Correct Answer: A
This patient has a normal anion gap metabolic acidosis which can be seen in patients abusing laxatives. Stool contains a significant amount of bicarbonate along with potassium and sodium. With increased amounts of diarrhea, bicarbonate is lost, leading to a metabolic acidosis. Other causes of normal anion gap metabolic acidosis include renal causes, such as RTA, which emphasizes the importance of measurement of the urine anion gap (UNa + UK − UCl ). The urine anion will aid in estimating the kidneys’ ability to excrete acid. A positive urine anion gap is suggestive of renal causes of a normal anion gap metabolic acidosis, whereas a negative urine anion gap points toward a gastrointestinal source, such as diarrhea.
The first step with this kind of presentation is to determine the type of acid-base and electrolyte disturbance. Once it is determined that it is a normal anion gap metabolic acidosis, the second step is to differentiate between renal causes versus extrarenal causes by calculating the urine anion gap; a positive urine anion gap points toward renal causes whereas a negative urine anion gap is mostly of gastrointestinal etiology.
A 43-year-old man is brought by the police to the emergency department after being found unresponsive on the street. He appears unkempt and disheveled. On physical examination, his temperature is 36.0°C, blood pressure is 146/92 mm Hg, pulse rate is 84 beats/min, and respiratory rate is 10 breaths/min. He is not oriented to time and place. Laboratory data show the following:
An arterial blood gas is also obtained which shows:
Which of the following is the MOST likely diagnosis in this patient?
The patient presents with an increased anion gap metabolic acidosis of 28—calculated anion gap = Na − (HCO3 + Cl). In addition, his serum bicarbonate level is reduced to 8 mEq/L with a plasma osmolal gap of 12 mOsm/kg H2O. Altogether, this points to ethylene intoxication. The osmolal gap is defined as the difference between the measured and the calculated plasma osmolality using the formula below:
Calculated plasma osmolality = (2 × plasma sodium) + glucose/18 + BUN/2.8
Ethylene glycol is commonly found in automotive coolants and cleaners, and ingestion of ethylene glycol will cause an increased anion gap metabolic acidosis with increased plasma osmolal gap of >10 mOsm/kg H2O. Of note, methanol poisoning will also lead to similar findings. Isopropyl poisoning will also have an increased osmolal gap of >10 mOsm/L, but it does not usually cause an anion gap metabolic acidosis.
An 87-year-old lady is being evaluated in the nursing home after being found to be more lethargic. She had been complaining of decreased appetite due to abdominal pain and ongoing diarrhea for the last 3 days. Her past medical history is significant for hypertension, type II diabetes mellitus, chronic back pain, and diverticulosis. Her medications include metformin, insulin, lisinopril, and naproxen. On physical examination, her:
Laboratories obtained show the following:
Correct Answer: E
The patient has a mixed acid-base disorder. Her pH is alkalotic. Upon closer look, it appears that she has a respiratory alkalosis (pCO2 20 mm Hg). To determine whether this is an acute or chronic respiratory alkalosis, the following formula can be used: 1-2-4-5 rule.
In acute respiratory alkalosis, for every decrease in PaCO2 by 10, the HCO3 − decreases by 2.
In chronic respiratory alkalosis, for every decrease in PaCO2 by 10, the HCO3 − decreases by 5.
Based on that, her expected HCO3 − is approximately 14 mEq/L. However, in this case, it is 21 mEq/L which is higher than expected. This suggests that there is concurrent metabolic alkalosis present. This is also confirmed by calculating the Δ-Δ ratio—(calculated AG – expected AG)/24 – measured HCO3 −—which aids in determining the presence of any other normal AG metabolic acidosis or if this is a pure high AG metabolic acidosis.
In this case, the Δ-Δ ratio is >1, indicating that there is in fact a metabolic alkalosis present. A Δ-Δ ratio < 1 suggests a normal AG metabolic acidosis.
A 32-year-old male is referred to the nephrologist for abnormal laboratory values. He was recently seen by his primary care physician for his annual physical examination. During his visit, he was told that his “urine was abnormal.” The patient does not have any known medical history except for a 26-year pack-year smoking history. He is normothermic with a blood pressure of 128/90 mm Hg, pulse rate of 58 beats/min, and respiratory rate of 12 breaths/min. The rest of his physical examination is unremarkable. His family history is only significant for arthritis and “thyroid disease.” Further laboratory studies obtained show the following:
What is the MOST likely diagnosis in this patient?
Correct Answer: B
This patient likely has RTA type 1. In patients with RTA type 1, there is impairment of acidification in the distal part of the nephrons. Because the kidney is unable to excrete hydrogen ions, this defect leads to the secretion of NH4+ . Patients with RTA type 1 usually have non–anion gap acidosis (which is also found in patients with RTA type 2 and 4). However, the main difference between the types of RTA is that type 1 will also have very low levels of HCO3 − , high urine pH of >5.5 (as the kidney is unable to maximally acidify the urine), and positive urine anion gap. In this case, the patient’s urine anion gap is 19 based on the formula, Urine anion gap = UNa + UK − UCl .
Main causes of RTA type I include autoimmune diseases, such as rheumatoid arthritis and Sjögren syndrome, obstructive nephropathy, and nephrotoxins, including toluene and amphotericin B. There is a hereditary cause for RTA type 1 which is usually diagnosed in infants or childhood. Though the clear mechanism of acquired RTA type I is unclear, it has been suggested that this due to defective H+ -K+ ATPase function at the apical surface of the α-type intercalated cells of the collecting duct.
In children, this can manifest with polyuria, stunted growth, recurrent nephrocalcinosis, and hypercalciuria. In adults, RTA type 1 will also lead to nephrocalcinosis. Treatment consists of managing the underlying disorders but can sometimes include usage of thiazide diuretics and/or NaHCO3 and K+ supplementation.
While all types of RTA lead to hyperchloremic non–anion gap metabolic acidosis, the main differences between types of RTA are laid out in the table below:
A 64-year-old woman is being treated in the local intensive care unit (ICU) for septic shock due to Streptococcus pneumoniae. She weighs 120 kg. She is started on empiric antibiotics and resuscitated with 30 mL/kg of normal saline without significant improvement. She is therefore temporarily started on vasopressor support. She improves after 4 days and is weaned off all vasopressors. She extubated to noninvasive ventilation. However, her voice remains hoarse, and she fails her swallow evaluation. She remains on intravenous fluids for hydration for 3-day history of diarrhea.
Laboratory data obtained on admission:
What is the MOST likely cause for her laboratory abnormalities?
Correct Answer: C
Iatrogenic causes of non–anion gap metabolic acidosis are common in the setting of critical ill patients, who require aggressive fluid administration, particularly when chloride-rich solutions such as 0.9% saline are used. When large amounts of sodium chloride–containing solutions are administered, the chloride concentration in the serum will rise more than that of sodium as the serum chloride levels are normally lower than serum sodium. Therefore, the strong ion difference (SID) decreases and leads to a reduction of the positive plasma charge. To compensate for this, the chloride reacts with bicarbonate to produce protons and buffer the pH. This leads to depletion of bicarbonate stores and subsequently an acidosis.
© 2010-2030 Your Doctor - Dr.Khalil Al-Yousifi - Kuwait - Contact Us