Q: Which equation is used to calculate the effective serum osmolarity?

$$\text{Osmolarity} = 2 \times [\text{Na}^+] + [\text{Glucose}]/18 + [\text{BUN}]/2.8$$

Q: A laboratory report shows a serum calcium of 7.5 mg/dL and an albumin of 2.0 g/dL. What is the corrected calcium using the following formula: $$\text{Corrected Ca} = \text{Measured Ca} + 0.8 \times (4.0 - \text{Albumin})$$?

$$7.5 + 0.8 \times (4.0 - 2.0) = 9.1 mg/dL$$

Q: A patient with hyperglycemia has a measured serum sodium of 130 mmol/L and a glucose of 600 mg/dL. Using the formula $$\text{Corrected Na} = \text{Measured Na} + 1.6 \times \left(\frac{\text{Glucose} - 100}{100}\right)$$, what is the corrected sodium?

$$130 + 1.6 \times \left(\frac{600 - 100}{100}\right) = 138$$ mmol/L

Q: A patient’s serum sodium is 140 mmol/L, glucose is 90 mg/dL, and BUN is 14 mg/dL. Calculate the effective serum osmolarity using the formula $$\text{Osmolarity} = 2 \times [\text{Na}^+] + [\text{Glucose}]/18 + [\text{BUN}]/2.8.$$

$$2 \times 140 + 90/18 + 14/2.8 = 280 + 5 + 5 = 290$$ mOsm/kg

Question 1

Which of the following laboratory tests is most commonly used to assess renal function in a clinical setting?

Accepted Answer

Blood urea nitrogen (BUN)

Question 2

A patient presents with confusion and muscle weakness. Laboratory results show a serum sodium of 120 mmol/L. Which of the following is the most likely clinical consequence of this electrolyte abnormality?

Accepted Answer

Seizures

Question 3

Which equation is used to calculate the effective serum osmolarity?

Accepted Answer

$$	ext{Osmolarity} = 2 	imes [	ext{Na}^+] + [	ext{Glucose}]/18 + [	ext{BUN}]/2.8$$

Question 4

A laboratory report shows a serum calcium of 7.5 mg/dL and an albumin of 2.0 g/dL. What is the corrected calcium using the following formula: $$	ext{Corrected Ca} = 	ext{Measured Ca} + 0.8 	imes (4.0 - 	ext{Albumin})$$?

Accepted Answer

$$7.5 + 0.8 	imes (4.0 - 2.0) = 9.1 mg/dL$$

Question 5

Which of the following is a common preanalytical error that can affect laboratory results?

Accepted Answer

Hemolysis of the blood sample

Question 6

A patient’s blood gas analysis reveals a pH of 7.25. Which of the following electrolyte changes is most likely to occur in response to this acidotic state?

Accepted Answer

Increase in serum potassium

Question 7

Which laboratory test is most specific for evaluating liver synthetic function?

Accepted Answer

Serum albumin

Question 8

A patient with hyperglycemia has a measured serum sodium of 130 mmol/L and a glucose of 600 mg/dL. Using the formula $$	ext{Corrected Na} = 	ext{Measured Na} + 1.6 	imes \left(\frac{	ext{Glucose} - 100}{100}ight)$$, what is the corrected sodium?

Accepted Answer

$$130 + 1.6 	imes \left(\frac{600 - 100}{100}ight) = 138$$ mmol/L

Question 9

Which of the following is NOT typically included in a basic metabolic panel (BMP)?

Accepted Answer

Serum albumin

Question 10

A patient’s laboratory results show hypomagnesemia. Which of the following clinical consequences is most likely associated with this finding?

Accepted Answer

Arrhythmias

Question 11

Which of the following mechanisms can cause hyperphosphatemia in a patient?

Accepted Answer

Renal failure

Question 12

Which laboratory test is most useful for monitoring anticoagulation therapy?

Accepted Answer

Prothrombin time (PT)

Question 13

A patient’s serum potassium is 6.5 mmol/L. Which of the following is the most appropriate initial intervention?

Accepted Answer

Administer intravenous calcium gluconate

Question 14

Which of the following is a postanalytical laboratory error?

Accepted Answer

Transcription of results into the wrong patient chart

Question 15

Which of the following is the best indicator of effective serum osmolarity?

Accepted Answer

Sodium concentration

Question 16

A patient with chronic kidney disease is most likely to have which of the following laboratory abnormalities?

Accepted Answer

Elevated serum phosphate

Question 17

Which of the following is a common analytical error in laboratory testing?

Accepted Answer

Instrument calibration error

Question 18

A patient’s serum sodium is 140 mmol/L, glucose is 90 mg/dL, and BUN is 14 mg/dL. Calculate the effective serum osmolarity using the formula $$	ext{Osmolarity} = 2 	imes [	ext{Na}^+] + [	ext{Glucose}]/18 + [	ext{BUN}]/2.8.$$

Accepted Answer

$$2 	imes 140 + 90/18 + 14/2.8 = 280 + 5 + 5 = 290$$ mOsm/kg

Question 19

Which of the following laboratory tests is most likely to be affected by changes in blood pH?

Accepted Answer

Serum calcium

Clinical Laboratory Assessment: Serum Electrolytes and Laboratory Measurement Overview

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