A non-fasting sample from a healthy group O secretor shows ALP 175 U/L (reference 40-130 U/L) with normal GGT, ALT and calcium. A fasting repeat is normal. The extra ALP was most likely:

Intestinal ALP released after a fatty meal

Liver ALP from early cholestasis

Placental-like ALP from a germ cell tumor

Bone ALP from increased osteoblast activity

Total serum ALP in a healthy 13-year-old is normally higher than in adults because of:

Osteoblast activity in growing bone

Immature hepatic excretion of ALP

Placental-like ALP from the gonads

A 64-year-old has hemoglobin 72 g/L (7.2 g/dL), MCV 121 fL, hypersegmented neutrophils, pancytopenia, a low haptoglobin and LD 3,600 U/L (reference 125-220 U/L). LD isoenzyme electrophoresis would most likely show:

The normal LD2 greater than LD1

Bone and muscle enzymes

5 DOH Abu Dhabi (HAAD) lab licensing practice questions on Bone and muscle enzymes, part of Clinical Chemistry. The first 5 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 · Medium
A 52-year-old woman has tiredness, weight gain, cold intolerance and muscle aches. CK is 640 U/L (reference below 170 U/L), almost all CK-MM, and troponin is normal. Which condition best explains the raised CK?
1. APrimary hypothyroidism
2. BAcute myocardial infarction
3. CThyrotoxicosis
4. DAlcoholic liver disease
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Answer: A · Primary hypothyroidism
Hypothyroidism causes a myopathy and slows CK clearance, so CK-MM often rises several-fold. Her symptoms fit, and CK falls once thyroxine is replaced. TSH should be checked in anyone with an unexplained persistently raised CK, including before starting a statin. Thyrotoxicosis usually gives a normal or low CK.
- B: A normal troponin argues against infarction.
- C: Hyperthyroidism usually gives a normal or low CK.
- D: Liver disease raises liver enzymes, not CK-MM.
Question 2 · Easy
Which LD isoenzyme is the main form in liver and skeletal muscle?
1. ALD2
2. BLD5
3. CLD3
4. DLD1
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Answer: B · LD5
LD5 (four M subunits) is the main form in liver and skeletal muscle and moves slowest on electrophoresis. LD1 and LD2 come mainly from heart, red cells and kidney, and LD3 from lung, spleen and lymphoid tissue. In normal serum LD2 is the largest fraction. LD4 and LD5 lose activity in the cold, so LD samples are kept at room temperature.
- A: LD2 is the largest fraction in normal serum but is not the main liver or muscle form.
- C: LD3 comes mainly from lung, spleen and lymphoid tissue.
- D: LD1 is the main form in heart and red cells.
Question 3 · Medium
A non-fasting sample from a healthy group O secretor shows ALP 175 U/L (reference 40-130 U/L) with normal GGT, ALT and calcium. A fasting repeat is normal. The extra ALP was most likely:
1. ALiver ALP from early cholestasis
2. BPlacental-like ALP from a germ cell tumor
3. CBone ALP from increased osteoblast activity
4. DIntestinal ALP released after a fatty meal
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Answer: D · Intestinal ALP released after a fatty meal
Intestinal ALP enters the blood for several hours after a fatty meal, mainly in people of blood group O or B who are secretors. It can push a borderline total ALP above the reference limit. A fasting sample removes the effect. Intestinal ALP, like placental ALP, is inhibited by L-phenylalanine.
- A: Cholestasis would raise GGT and would persist when fasting.
- B: A tumor isoenzyme would not disappear on fasting.
- C: Bone ALP does not vary with meals.
Question 4 · Easy
Total serum ALP in a healthy 13-year-old is normally higher than in adults because of:
1. AOsteoblast activity in growing bone
2. BImmature hepatic excretion of ALP
3. CPlacental-like ALP from the gonads
4. DIntestinal ALP from fatty food
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Answer: A · Osteoblast activity in growing bone
Bone ALP comes from osteoblasts, which are very active during growth. In the pubertal growth spurt, total ALP can be several times the adult upper limit. A normal GGT confirms that the extra ALP is not from the liver. Results must be judged against age-specific reference ranges.
- B: The liver is mature by this age and is not the source.
- C: Placental-like (germ cell) ALP is a tumor marker and does not cause growth-related rises.
- D: Intestinal ALP gives only small rises after meals.
Question 5 · Hard
A 64-year-old has hemoglobin 72 g/L (7.2 g/dL), MCV 121 fL, hypersegmented neutrophils, pancytopenia, a low haptoglobin and LD 3,600 U/L (reference 125-220 U/L). LD isoenzyme electrophoresis would most likely show:
1. ALD1 greater than LD2
2. BLD3 as the dominant fraction
3. CLD5 as the dominant fraction
4. DThe normal LD2 greater than LD1
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Answer: A · LD1 greater than LD2
In megaloblastic anemia many red cell precursors die in the marrow (ineffective erythropoiesis) and release their LD1 and LD2. LD can become very high, and LD1 rises above LD2, the flipped pattern also seen in hemolysis. Haptoglobin falls and indirect bilirubin rises for the same reason. A very high LD with macrocytosis should prompt vitamin B12 and folate testing.
- B: LD3 rises mainly in lung disease and lymphoid disorders.
- C: LD5 dominates in liver injury and skeletal muscle damage.
- D: Ineffective erythropoiesis releases LD1, reversing the normal LD2 > LD1 order.

Bone and muscle enzymes

A 52-year-old woman has tiredness, weight gain, cold intolerance and muscle aches. CK is 640 U/L (reference below 170 U/L), almost all CK-MM, and troponin is normal. Which condition best explains the raised CK?

Which LD isoenzyme is the main form in liver and skeletal muscle?

A non-fasting sample from a healthy group O secretor shows ALP 175 U/L (reference 40-130 U/L) with normal GGT, ALT and calcium. A fasting repeat is normal. The extra ALP was most likely:

Total serum ALP in a healthy 13-year-old is normally higher than in adults because of:

A 64-year-old has hemoglobin 72 g/L (7.2 g/dL), MCV 121 fL, hypersegmented neutrophils, pancytopenia, a low haptoglobin and LD 3,600 U/L (reference 125-220 U/L). LD isoenzyme electrophoresis would most likely show: