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Q.1- What is the range of serum creatinine in normal health?

Answer- The serum creatinine ranges between

1) In children (<12 years) 0.25-0.85 mg/dl

2) Adult male 0.7-1.5 mg/dl

3) Adult female 0.4-1.2 mg/dl

Q.2- What are the conditions of high serum creatinine levels?

Answer- Higher levels are observed in – Renal failure (All causes) and in muscular dystrophies. Falsely high levels are observed in diabetic ketoacidosis.

Q.3- If in a patient, serum creatinine has been found to be higher than normal but blood urea is within the normal range, what is the likely possibility?

Answer- It can not be renal failure because in such a state both blood urea and serum creatinine should have been higher, since both are excreted by kidney through urine in normal health. But since blood urea is normal, it could be any other reason and the most likely cause is muscular dystrophy. The diagnosis can be made from the history and clinical symptoms. The other possibility can be of false high value as in diabetic keto acidosis.

Q.4- In a patient with normal serum creatinine level, blood urea has been found to be much higher than normal, what could be the possibility?

Answer- Both urea and creatinine should be higher than normal in renal failure, if creatinine is normal the possibility of renal failure can be ruled out. Blood urea can be higher than normal in conditions of- Advancing age, high protein diet, dehydration, catabolic state and in post renal obstructive conditions (Stone, stricture, growth etc)

Q.5- What is the principle of alkaline picrate method (Jaffe’s reaction) for the estimation of serum creatinine?

Answer- Creatinine under alkaline conditions reacts with Picric acid to form Creatinine picrate (An orange-red colored complex), the intensity of which is measured at 520 nm.

Q.- 6- Alkaline picrate method is considered a less sensitive method for creatinine estimation, what are the other substances which can give a positive reaction with alkaline picrate?

Answer- Jaffe’s reaction is not specific for creatinine. In serum up to 20% of the total chromogens (Color forming substances) can be substances other than creatinine which give a positive reaction with alkaline picrate, while in urine these are only 5%. Other non specific chromogens that react with Picric acid are – proteins, ketone bodies, pyruvate, glucose and Ascorbate.

Q.7- What is the difference between creatine and creatinine?

Answer- Creatinine is the anhydrous product of creatine. Creatine is converted to creatinine non enzymatically by the loss of one molecule of water. About 2 % of creatine is converted to Creatinine daily.

Q.8- Which form out of creatine and creatinine is present in urine in normal health?

Answer- In normal urine creatinine is mainly present, creatine is present only in trace amounts.

Q.9-Name the amino acids that contribute towards creatine synthesis

Answer- Creatine is synthesized from Glycine, Arginine and Methionine. In the first step, Glycine and Arginine combine together to form Guanido Acetic acid, this reaction takes place in kidney. In the second step, Guanido acetic acid is methylated by Methionine to form Methyl Guanido acetic acid (Creatine). This reaction takes place in liver. Creatine is transported to muscles, where it is phosphorylated and stored in the form of creatine-P. 98% of the total amount of creatine is present in muscles.

Q.10- What is Lohmann reaction?

Answer- Creatine is phosphorylated to creatine-P by the enzyme Creatine kinase, present in muscle, brain and myocardium. The stored creatine phosphate in the muscle serves as an immediate source of energy. During muscle contraction, the energy is first derived from ATP hydrolysis. Thereafter, the ATP is generated by the -hydrolysis of creatine-P. The high energy phosphate is transferred to ADP to form ATP. This reaction is called Lohmann reaction.  In the resting muscles the creatine-P is restored at the expense of ATP provided from glycolysis.

Q.11- What are the common causes of creatinuria?

Answer- Excretion of creatine in urine is called Creatinuria, which is observed under the following conditions-

1) In children- Probably due to impaired conversion of creatine to creatinine

2) Pregnancy

3) Febrile conditions

4) Thyrotoxicosis

5) Muscular dystrophies, myositis and Myasthenia gravis

6) Uncontrolled diabetes mellitus

7) Starvation

8) Wasting diseases- such as Malignancies.

Q.12- What is creatinine co-efficient? What is its significance?

Answer- It is the ratio of- mg of creatinine in urine in 24 hours/ Body weight in kg.

The value is 20-26 for males and 14 to 22 in females.

Significance- It depends on muscle mass and remains fairly constant. Since muscle mass remains constant in a given individual, the creatine coefficient serves as a reliable index of the adequacy of a 24 hour urine collection

Q.13- What is the reason for high creatinine level in males in normal health?

Answer- Creatine is synthesized in liver, passes in to circulation and is almost taken entirely by the skeletal muscle for conversion to creatine-P, which serves as a storage form of energy in skeletal muscles. About 2% of creatine is converted to Creatinine daily. Since its concentration is related to the muscle mass and males have more muscle mass that is why the level of serum creatinine is higher in males in normal health.

Q.14- What is the normal range of creatinine clearance? What is the significance of measuring creatinine clearance?

Answer- The normal values of creatinine clearance are-

Males- 95-140 ml/minute

Females-85-125 ml/minute

These values are close to GFR (Glomerular filtration rate). Clearance values are decreased in impaired renal functions and so provide a rough measure of renal damage.

Q.15- Out of urea and creatinine clearance, the estimation of which clearance is preferred to assess renal functional status and why?

Answer- Unlike urea, serum Creatinine level is not affected by diet, age, dietary factors or by fluid depletion. Creatinine is filtered but is not absorbed by the tubules (unlike urea), hence it is a better predictor of GFR. (The values are slightly higher than GFR due to tubular secretion). The methodology is also simple, due to all these reasons; creatinine clearance is preferred over urea clearance for determining the functional status of the kidney.

Q.16-   Calculate the creatinine clearance of a patient with serum creatinine of 3 mg/dL, volume of urine excreted 1500 ml/ day and urinary creatinine of 0.75 G/L 

Answer- Creatinine clearance(C)= UV/P

Where U= Urinary creatinine (mg/dl)

V= Volume of urine excreted (ml/day)

P= Serum Creatinine (mg/dl)

Thus applying the values-

V= 1500 ml/day, convert to ml/ minutes

i.e. = 1500/24×60= 1.1 ml/minute (Approximately)

U= 0.75 G/L, Convert it to mg/dl

i.e. – 75 mg/dl

Creatinine clearance (C) = 75×1.1/3

   = 27.5 ml/minute

It is much below the physiological range; hence it is a case of impaired renal functions.

Q.17- Comment upon the functional status of the kidney, if the serum creatinine is 4.5 mg/dL, blood urea- 86 mg/dL  and serum uric acid as 12 mg/dl.

Answer- Urea, creatinine and uric acid are normally excreted by kidney through urine, since the levels of three of them are higher than normal in the given case that means kidney is failing to clear out these substances from blood that is why they are accumulating in blood, hence it is a case of impaired renal functions, possibly renal failure.

Q.18- A patient with long-standing diabetes mellitus has reported to emergency with generalized swelling of the body. Blood biochemistry reveals-

Hb- 8 G/dL

F.B.S- 260 mg/dl

Blood urea- 98 mg/dl

Serum creatinine- 3.4 mg/dL

Serum Uric acid- 10.8 mg/Dl

Urine analysis- Sugar ++++


Urea clearance 32 ml/minute

Creatinine clearance- 68 ml/minute

Comment on the findings and provide a provisional diagnosis.

Answer- It is a case of renal failure due to long-standing diabetes mellitus. Blood urea, serum creatinine and uric acid are high, clearance values are low, Hb is low due to decreased Erythropoietin, sugar and protein in urine are suggestive of Diabetic nephropathy which has progressed to renal failure.

Q.19- Out of serum creatinine and blood urea, which is more sensitive indicator of falling renal functions?

Answer- Serum creatinine is more sensitive indicator of falling renal functions than blood urea.  Urea level is affected by non renal causes also, while creatinine is a relatively a stable parameter, hence its measurement carries more significance to assess falling functional status of the kidney.

Q.20- In a patient with diabetic ketoacidosis, creatinine is high while blood urea is normal, what is the possibility?

Answer- Jaffe’s reaction for estimation of serum creatinine gives positive reaction with Glucose and ketone bodies also, which are high in diabetic ketoacidosis. It is falsely high level due to other chromogens and not due to creatinine. Normal blood urea level indicates normal renal functions.

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