Measurements of Creatinine: Serum Components that Interfere with Jaffe Method? (Lab Report Sample)

MEASUREMENTS OF CREATININE
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Reactions that are involved during determination of creatinine concentration using Jaffe’s method.
The Jaffe method which is used to determine serum creatinine involves reacting creatinine with picric acid in an alkaline medium of sodium hydroxide solution and measured at 520nm (Gaw 2004). The reactions are as shown below in diagram i.
Diagram i. Creatinine and picric acid reaction (Burtis 2015)
Serum components that interfere with Jaffe method?
Because of its non-specificity of this reaction in relation to creatinine, this method is affected by presence of chromogens such as proteins, acetoacetate, acetone, cephalosporins, ascorbic acid, ketone bodies, and guanidine (Ahmed 2013). The interference cause false creatinine concentration. Other interferences such as haemolysis show results that are falsely elevated; lipemia shows decreased results which is false and icteremia which causes falsely lower results (Gaw 2004).
Reason why absorbance values for serum creatinine change after the addition of 30% acetic acid?
Addition of acetic acid interferes with the absorbance of creatinine by inducing an acid medium which destroys the alkalinity of the medium.
If the urine creatinine concentration is 3.4mmol/L, the plasma creatinine 85mol/L and the 24 hour urine volume is 2160 ml, what is the creatinine clearance rate?
The creatinine clearance rate is calculated by multiplying concentration of creatinine in urine with urine flow rate and then dividing the answer by the concentration of creatinine in plasma (Lambert 2004). First, the urine flow rate is calculated by dividing the total amount of urine by the total minutes in 24 hours.
Urine flow rate=24x60=1440
2160 ÷ 1440=1.5ml/min
= 3.4mmol/L × 1.5 ml/min ÷0.085mmol/L= 60ml/min
RENAL FUNCTION
Define estimate Glomerular Filtrate Rate (eGFR). What is the purpose of estimating eGFR?
The estimate Glomerular Filtrate Rate (eGFR) is the rate at which fluid in blood is filtered by the kidney to the Bowman’s capsule per unit time (Burtis 2015). This is done because of the following reasons;
* Monitor disease progress.
* To detect any impairment of the kidney.
* To enable doctors to set a baseline measures that can be used when patient new medications for specific drugs.
Compare and contrast the renal function of the following two patients:
* A frail, 81-year-old woman who weighs 52 kg with a serum creatinine of 109 µmol/L and an eGFR that has been calculated as 44 mL/ min/1.73m2.
* A muscular, 24-year-old man who weighs 89 kg with a serum creatinine of 104 µmol/L and an eGFR that has been calculated as >60 mL/min/1.73m2.
Explain why these patients have similar creatinine concentrations but very different renal functions
This is due to the fact that during calculation, the body surface area is included (Ahmed 2013). One of the patients has a weight of 52 kg while the other has a weight of 89 kg.
INTERFERENCE
Below are examples of common endogenous interferences in serum samples
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Identify each of the serum samples shown above, stating any possible reasons for the change in colour or turbidity. What impact might these changes have on clinical chemical analyses?
The first tube represents lipemia interference which contains high levels of lipoproteins (Ahmed 2013). The second tube represents haemolysis due to the colour haemoglobin. The third tube represents serum sample containing antibodies while tube four represents serum sample containing bicarbonate ions. These changes results in a false concentration of creatinine concentration in serum samples which in turn give wrong indication about the state of the kidney (Burtis 2015).
A patient’s blood sample was taken at 9am and found to be haemolysed. The blood sample was repeated at 11am. Results of both tests are given below.
9am sample11am
Sodium134135(137-143 mmol/L)
Potassium7.34.9(3.5-5.0 mmol/L)
Urea2526(2.5-7.5 mmol/L)
Creatinine35698<100 umol/L
Phosphate2.91.3(0.5-1.5 mmol/L)
Calcium2.422.43(2.2-2.6 mmol/L)
Creatine Kinase1700205<275 IU/L
LDH4530492<450 IU/L
ALT4539<45 IU/L
ALKP102110<125 IU/L
Which of the samples was affected by haemolysis?
The blood sample that was taken at 9 am showed to haemolysed.
What are the causes of haemolysis?
Haemolysis is the process where erythrocytes disintegrate releasing their haemoglobin contents into blood (Ahmed 2013). This can occur either in the body (in vivo) or outside the body (in vitro). Haemolysis is caused by several factors and this depends on the inside or outside the body (Lambert 2004). Haemolysis outside the body is due to the following;
* Poor techniques used to collect blood sample.
* Bacterial action on the blood sample for example cultured blood sample.
* Blood undergoing mechanical processing during procedure of surgery.
In vivo haemolysis on the other hand can be as a result of the following factors;
* Through the action of bacteria such as Gram positive bacteria for example Staphylococcus.
* Parasite action in blood sample such as Plasmodium.
* Through automated immune disorders which are caused by drugs.
* It can also be due the genetic make-up of an individual which such as individuals with single-cell disorder.
How are the above analytes in the blood samples affected?
The analytes above were affected i...