A 66-year-old woman has a raised total protein on a routine panel. Workup shows an IgG kappa monoclonal protein of 2.4 g/dL [24 g/L], a serum free light chain kappa/lambda ratio of 22 (reference 0.26-1.65), and 18% clonal plasma cells in the bone marrow. Hemoglobin 12.8 g/dL [128 g/L], calcium 9.6 mg/dL [2.40 mmol/L] (reference 8.6-10.2), creatinine 0.9 mg/dL [80 µmol/L]. Whole-body low-dose CT shows no lytic lesions, and MRI shows no focal lesions. Using International Myeloma Working Group criteria, which diagnosis do these results support?

Monoclonal gammopathy of undetermined significance

Active multiple myeloma needing treatment

A 59-year-old man has his first attack of gout and a history of uric acid kidney stones. He takes no diuretics or aspirin and drinks little alcohol. Results: hemoglobin 19.4 g/dL [194 g/L], hematocrit 58%, WBC 12.8 x 10^3/µL [12.8 x 10^9/L], platelets 610 x 10^3/µL [610 x 10^9/L], JAK2 V617F detected, serum uric acid 10.2 mg/dL [607 µmol/L], creatinine 1.0 mg/dL [88 µmol/L]. After 5 days on a purine-restricted diet, his 24-hour urine uric acid is 840 mg [5.0 mmol] (reference on this diet below 600 mg [3.6 mmol] per day). The hyperuricemia is best explained by:

Overproduction from increased cell turnover

Urate retention from early kidney failure

Reduced renal excretion of uric acid

A 63-year-old man has black, tarry stools. BUN 52 mg/dL [18.6 mmol/L], creatinine 1.1 mg/dL [97 µmol/L], hemoglobin 8.6 g/dL [86 g/L]. The raised BUN with a normal creatinine is best explained by:

Absorption of digested blood protein

Obstruction of the urinary tract

Acute tubular necrosis from blood loss

Reduced urea synthesis in the liver

Proteins and nitrogen compounds: interpretation and disease correlation

22 ASCP MLS practice questions on Proteins and nitrogen compounds: interpretation and disease correlation, part of Chemistry. The first 22 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 52-year-old man with a body surface area of 2.10 m² is investigated for proteinuria. He collects an overnight 12-hour urine from 20:00 to 08:00, emptying his bladder at 20:00 and discarding that urine, and including the 08:00 void. Urine volume 600 mL; urine creatinine 120 mg/dL [10.6 mmol/L]. Serum creatinine drawn at 08:00 is 0.9 mg/dL [80 µmol/L]. The collection is judged complete. What is his creatinine clearance corrected to a body surface area of 1.73 m²?
1. A46 mL/min/1.73 m²
2. B92 mL/min/1.73 m²
3. C135 mL/min/1.73 m²
4. D111 mL/min/1.73 m²
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Answer: B · 92 mL/min/1.73 m²
Clearance = (urine creatinine x urine volume) / (serum creatinine x time) = (120 x 600) / (0.9 x 720) = 72,000 / 648 = 111 mL/min. The collection lasted 12 hours, so the time is 720 minutes, not the 1,440 minutes of a 24-hour collection. Correcting to standard body size: 111 x 1.73 / 2.10 = 92 mL/min/1.73 m². A larger person makes and filters more creatinine, so the corrected value is lower than the raw one. Urine and serum creatinine must be in the same units for the calculation.
- A: 46 uses 1,440 minutes, but this was a 12-hour (720-minute) collection.
- C: 135 comes from multiplying by 2.10/1.73, which inverts the body size correction.
- D: 111 mL/min is the uncorrected clearance; it was not adjusted for his larger body size.
Question 2 · Hard
A 66-year-old woman has a raised total protein on a routine panel. Workup shows an IgG kappa monoclonal protein of 2.4 g/dL [24 g/L], a serum free light chain kappa/lambda ratio of 22 (reference 0.26-1.65), and 18% clonal plasma cells in the bone marrow. Hemoglobin 12.8 g/dL [128 g/L], calcium 9.6 mg/dL [2.40 mmol/L] (reference 8.6-10.2), creatinine 0.9 mg/dL [80 µmol/L]. Whole-body low-dose CT shows no lytic lesions, and MRI shows no focal lesions. Using International Myeloma Working Group criteria, which diagnosis do these results support?
1. ASolitary plasmacytoma of bone
2. BMonoclonal gammopathy of undetermined significance
3. CSmoldering multiple myeloma
4. DActive multiple myeloma needing treatment
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Answer: C · Smoldering multiple myeloma
IMWG criteria separate these disorders by marrow plasma cells, M-protein and myeloma-defining events. Clonal plasma cells of 10-59% (here 18%) or a serum M-protein of 3 g/dL or more, without any myeloma-defining event, define smoldering myeloma. Myeloma-defining events are CRAB features (hypercalcemia, renal failure, anemia, bone lesions) or a biomarker: 60% or more plasma cells, an involved/uninvolved free light chain ratio of 100 or more, or more than one focal lesion on MRI. She has none of these, so she is monitored rather than treated. MGUS would need fewer than 10% marrow plasma cells.
- A: A plasmacytoma is a single lesion with little or no marrow involvement; no lesion is seen here.
- B: MGUS needs fewer than 10% marrow plasma cells and an M-protein below 3 g/dL; she has 18% plasma cells.
- D: There are no CRAB features, no lesions, and the light chain ratio is below 100.
Question 3 · Hard
A 59-year-old man has his first attack of gout and a history of uric acid kidney stones. He takes no diuretics or aspirin and drinks little alcohol. Results: hemoglobin 19.4 g/dL [194 g/L], hematocrit 58%, WBC 12.8 x 10^3/µL [12.8 x 10^9/L], platelets 610 x 10^3/µL [610 x 10^9/L], JAK2 V617F detected, serum uric acid 10.2 mg/dL [607 µmol/L], creatinine 1.0 mg/dL [88 µmol/L]. After 5 days on a purine-restricted diet, his 24-hour urine uric acid is 840 mg [5.0 mmol] (reference on this diet below 600 mg [3.6 mmol] per day). The hyperuricemia is best explained by:
1. AUrate retention from early kidney failure
2. BReduced renal excretion of uric acid
3. COverproduction from increased cell turnover
4. DA high dietary purine intake
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Answer: C · Overproduction from increased cell turnover
A 24-hour urine uric acid on a purine-restricted diet separates people who overproduce urate from those who underexcrete it. More than about 600 mg [3.6 mmol] a day on this diet means overproduction; most people with gout excrete less and are underexcretors. The high hemoglobin, hematocrit and platelets with a JAK2 V617F mutation indicate polycythemia vera, in which rapid turnover of marrow cells releases purines that are broken down to uric acid. Overproducers also have a higher risk of uric acid stones, as here. Xanthine oxidase inhibitors such as allopurinol suit this group.
- A: His creatinine is normal.
- B: His urine uric acid is high, not low, so the kidneys are excreting more urate.
- D: The urine was collected on a purine-restricted diet.
Question 4 · Hard
A 63-year-old man has black, tarry stools. BUN 52 mg/dL [18.6 mmol/L], creatinine 1.1 mg/dL [97 µmol/L], hemoglobin 8.6 g/dL [86 g/L]. The raised BUN with a normal creatinine is best explained by:
1. AObstruction of the urinary tract
2. BAcute tubular necrosis from blood loss
3. CReduced urea synthesis in the liver
4. DAbsorption of digested blood protein
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Answer: D · Absorption of digested blood protein
Blood in the upper GI tract is digested like a high-protein meal, and the liver turns the absorbed amino acids into urea. Blood loss also lowers kidney perfusion, which raises BUN further. Creatinine is unaffected, so the ratio here is about 47. A high BUN/creatinine ratio with melena favors an upper rather than lower GI source.
- A: Obstruction raises both BUN and creatinine.
- B: Tubular necrosis would raise creatinine as well.
- C: Reduced liver synthesis would lower BUN.
Question 5 · Medium
BUN 56 mg/dL [20.0 mmol/L] and creatinine 1.6 mg/dL [141 µmol/L]. The BUN/creatinine ratio of 35 is most consistent with:
1. APrerenal azotemia
2. BSevere liver disease
3. CAcute tubular necrosis
4. DA low-protein diet
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Answer: A · Prerenal azotemia
BUN rises more than creatinine when kidney blood flow falls, because slow tubular flow lets more urea be reabsorbed, while creatinine is not reabsorbed. A ratio above 20 with raised values is typical of prerenal azotemia, as in dehydration, heart failure or shock. Here 56 / 1.6 = 35. Restoring perfusion usually brings both values down.
- B: Severe liver disease lowers BUN and the ratio.
- C: Acute tubular necrosis raises creatinine along with BUN, with a ratio usually 10 to 15.
- D: A low-protein diet lowers BUN and the ratio.
Question 6 · Easy
What is the most common cause of a markedly raised plasma ammonia in adults?
1. AMultiple myeloma
2. BPrimary gout
3. CAcute kidney injury
4. DSevere liver disease
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Question 7 · Easy
Gout is caused by excess uric acid, which in humans is the final breakdown product of:
1. ABranched-chain amino acids
2. BCreatine phosphate
3. CPyrimidine bases
4. DPurine bases
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Question 8 · Medium
Creatinine clearance tends to overestimate the true GFR, more so as kidney function falls. The reason is that creatinine is:
1. AAlso secreted by the proximal tubules
2. BPartly reabsorbed by the collecting ducts
3. CMostly broken down by the liver
4. DTightly bound to plasma albumin
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Question 9 · Medium
The International Staging System (ISS) for multiple myeloma uses which two serum tests?
1. ACalcium and creatinine
2. BLD and uric acid
3. CBeta-2 microglobulin and albumin
4. DTotal protein and M-protein
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Question 10 · Hard
A 71-year-old man has back pain, lytic bone lesions and anemia (Hb 9.0 g/dL [90 g/L]). Total protein 5.6 g/dL [56 g/L]; albumin 3.8 g/dL [38 g/L]; calcium 11.8 mg/dL [2.94 mmol/L] (reference 8.6-10.3 mg/dL); creatinine 2.6 mg/dL [230 µmol/L]. SPEP shows low gamma globulin and no spike. The most likely diagnosis is:
1. ALight chain (Bence Jones) myeloma
2. BPrimary hyperparathyroidism
3. CIgG multiple myeloma
4. DWaldenström macroglobulinemia
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Question 11 · Hard
An 80-kg man collects a 24-hour urine: volume 800 mL, urine creatinine 75 mg/dL [6.6 mmol/L]. Serum creatinine is 1.1 mg/dL [97 µmol/L], and the calculated clearance is 38 mL/min. Daily creatinine excretion for his size should be about 1.6 to 2.0 g [14 to 18 mmol]. The most likely explanation is:
1. AHigh meat intake before the test
2. BTubular secretion of creatinine
3. CTrue loss of GFR to 38 mL/min
4. DAn incomplete 24-hour urine collection
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Question 12 · Hard
A 52-year-old man has sudden pain, redness and swelling of the big toe joint. His serum uric acid is 6.4 mg/dL [381 µmol/L] (reference 3.5-7.2 mg/dL). How should this result be interpreted?
1. AGout is excluded at this level
2. BSeptic arthritis is confirmed at this level
3. CGout is still possible at this level
4. DPseudogout is confirmed at this level
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Question 13 · Medium
Which set of results is most typical of multiple myeloma at diagnosis?
1. AHigh calcium, high total protein, normal or low albumin
2. BLow calcium, high phosphate, high PTH, high creatinine
3. CNormal calcium, low total protein, very low albumin
4. DHigh calcium, low phosphate, high PTH, normal total protein
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Question 14 · Easy
In a healthy adult on a normal diet, the serum BUN-to-creatinine ratio is usually about:
1. A1:1 to 5:1
2. B50:1 to 100:1
3. C25:1 to 40:1
4. D10:1 to 20:1
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Question 15 · Hard
A 9-year-old boy with Burkitt lymphoma has these results 24 hours after starting chemotherapy: uric acid 13.5 mg/dL [803 µmol/L], potassium 6.3 mmol/L, phosphate 8.4 mg/dL [2.71 mmol/L], calcium 6.9 mg/dL [1.72 mmol/L], creatinine 1.9 mg/dL [168 µmol/L], CK normal. The most likely cause is:
1. ARhabdomyolysis
2. BPrimary hyperparathyroidism
3. CIn vitro hemolysis
4. DTumor lysis syndrome
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Question 16 · Medium
Most people with primary gout have hyperuricemia mainly because of:
1. AA diet very high in purines
2. BRapid cell turnover in leukemia
3. COverproduction from HGPRT deficiency
4. DReduced renal excretion of urate
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Question 17 · Hard
A 5-day-old girl feeds poorly and is increasingly drowsy. Tandem mass spectrometry of her newborn screen shows raised leucine/isoleucine and valine, with alloisoleucine present. What is the most likely diagnosis?
1. AOrnithine transcarbamylase deficiency
2. BMaple syrup urine disease
3. CTyrosinemia type I
4. DPhenylketonuria
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Question 18 · Medium
BUN 5 mg/dL [1.8 mmol/L] and creatinine 1.0 mg/dL [88 µmol/L] give a BUN/creatinine ratio of 5. Which condition best explains this?
1. ACongestive heart failure
2. BSevere liver disease
3. CDehydration
4. DUpper GI bleeding
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Question 19 · Hard
24-hour urine: volume 1,800 mL; urine creatinine 84 mg/dL [7.4 mmol/L]. Serum creatinine 1.4 mg/dL [124 µmol/L]. What is the creatinine clearance, without body surface area correction?
1. A75 mL/min
2. B105 mL/min
3. C147 mL/min
4. D108 mL/min
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Question 20 · Hard
24-hour urine: volume 960 mL; urine creatinine 90 mg/dL [8.0 mmol/L]. Serum creatinine 1.0 mg/dL [88 µmol/L]. Body surface area is 1.20 m². What is the creatinine clearance corrected to 1.73 m²?
1. A60 mL/min/1.73 m²
2. B87 mL/min/1.73 m²
3. C104 mL/min/1.73 m²
4. D42 mL/min/1.73 m²
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Question 21 · Hard
A full-term boy feeds well for 2 days, then becomes lethargic and feeds poorly. Plasma ammonia is 700 µg/dL [411 µmol/L]. Blood gas: pH 7.51, pCO2 28 mm Hg. Anion gap and glucose are normal, and urine ketones are negative. What is the most likely cause?
1. AA urea cycle defect
2. BAn organic acidemia
3. CClassic phenylketonuria
4. DMaple syrup urine disease
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Question 22 · Medium
A 2-year-old boy has developmental delay, bites his lips and fingers, and leaves orange sand-like crystals in his diapers. Serum uric acid is markedly raised. Which enzyme is most likely deficient?
1. AHGPRT
2. BAdenosine deaminase
3. CPhenylalanine hydroxylase
4. DXanthine oxidase
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Proteins and nitrogen compounds: interpretation and disease correlation

A 63-year-old man has black, tarry stools. BUN 52 mg/dL [18.6 mmol/L], creatinine 1.1 mg/dL [97 µmol/L], hemoglobin 8.6 g/dL [86 g/L]. The raised BUN with a normal creatinine is best explained by:

BUN 56 mg/dL [20.0 mmol/L] and creatinine 1.6 mg/dL [141 µmol/L]. The BUN/creatinine ratio of 35 is most consistent with:

What is the most common cause of a markedly raised plasma ammonia in adults?

Gout is caused by excess uric acid, which in humans is the final breakdown product of:

Creatinine clearance tends to overestimate the true GFR, more so as kidney function falls. The reason is that creatinine is:

The International Staging System (ISS) for multiple myeloma uses which two serum tests?

An 80-kg man collects a 24-hour urine: volume 800 mL, urine creatinine 75 mg/dL [6.6 mmol/L]. Serum creatinine is 1.1 mg/dL [97 µmol/L], and the calculated clearance is 38 mL/min. Daily creatinine excretion for his size should be about 1.6 to 2.0 g [14 to 18 mmol]. The most likely explanation is:

A 52-year-old man has sudden pain, redness and swelling of the big toe joint. His serum uric acid is 6.4 mg/dL [381 µmol/L] (reference 3.5-7.2 mg/dL). How should this result be interpreted?

Which set of results is most typical of multiple myeloma at diagnosis?

In a healthy adult on a normal diet, the serum BUN-to-creatinine ratio is usually about:

A 9-year-old boy with Burkitt lymphoma has these results 24 hours after starting chemotherapy: uric acid 13.5 mg/dL [803 µmol/L], potassium 6.3 mmol/L, phosphate 8.4 mg/dL [2.71 mmol/L], calcium 6.9 mg/dL [1.72 mmol/L], creatinine 1.9 mg/dL [168 µmol/L], CK normal. The most likely cause is:

Most people with primary gout have hyperuricemia mainly because of:

A 5-day-old girl feeds poorly and is increasingly drowsy. Tandem mass spectrometry of her newborn screen shows raised leucine/isoleucine and valine, with alloisoleucine present. What is the most likely diagnosis?

BUN 5 mg/dL [1.8 mmol/L] and creatinine 1.0 mg/dL [88 µmol/L] give a BUN/creatinine ratio of 5. Which condition best explains this?

24-hour urine: volume 1,800 mL; urine creatinine 84 mg/dL [7.4 mmol/L]. Serum creatinine 1.4 mg/dL [124 µmol/L]. What is the creatinine clearance, without body surface area correction?

24-hour urine: volume 960 mL; urine creatinine 90 mg/dL [8.0 mmol/L]. Serum creatinine 1.0 mg/dL [88 µmol/L]. Body surface area is 1.20 m². What is the creatinine clearance corrected to 1.73 m²?

A full-term boy feeds well for 2 days, then becomes lethargic and feeds poorly. Plasma ammonia is 700 µg/dL [411 µmol/L]. Blood gas: pH 7.51, pCO2 28 mm Hg. Anion gap and glucose are normal, and urine ketones are negative. What is the most likely cause?

A 2-year-old boy has developmental delay, bites his lips and fingers, and leaves orange sand-like crystals in his diapers. Serum uric acid is markedly raised. Which enzyme is most likely deficient?