Blood Tests For Kidney Infection - Prep, Procedure, Results Interpretaiton
Tests & Procedures

Blood Tests To Diagnose Kidney Infection

The kidney is one of the vital organs in the human body. It filters waste products of the blood into urine and excretes from the body. Any dysfunction of the kidneys can result in the accumulation of waste products in blood along with excess fluid. Infection is a major cause which can cause acute kidney injury and sometimes can proceed into chronic renal failure.

Prompt diagnosis and treatment are essential to prevent complications which occur due to a chronic kidney infection. Children are more susceptible to develop complications due to kidney infection. This is because post infection induced kidney injury scarring can occur in the developing kidney of the child. In order to minimize the bad outcomes, the clinicians practice many diagnostic blood tests for a kidney infection.

Blood Tests For Kidney Infection

Full Blood Count

One of the basic blood tests for kidney infection diagnosis is full blood count with separate cell counts. The test does not need any specific prior preparation. The test can be performed as a first line investigation in any patient who is suspected to be having a kidney infection.


The blood will be drawn from a peripheral vein. 5-10ml of blood is drawn from a syringe and collected into a bottle with an anticoagulant to prevent the blood from getting clotted. Then the sample will be sent to the laboratory as soon as possible for the analysis.

Results Interpretation

The white blood cell count and the differential counts are the main focus in the report. Elevated total white blood cell count will guide the clinician towards an ongoing infection. Elevated levels of neutrophil count will suggest the infection to be in bacterial origin while a lymphocytic count will suggest it to be a viral infection. Bacterial infections are commoner than viral infections.

Antibiotic Sensitivity Test (ABST)

Blood culture with Antibiotic Sensitivity Test (ABST) is another important blood test for a kidney infection. If the infective organism has spread into the bloodstream, it can be isolated and identified via a blood culture test.


Before drawing blood for the test, the healthcare worker must gather the necessary clinical material. Healthcare worker must maintain sterility throughout the procedure because any contamination of the sample can result in false positivity in the test.

Firstly two pairs of sterile gloves are worn. Then the site of the venepuncture is cleaned with povidone-iodine and 90% alcohol. Then one pair of gloves is removed and blood is drawn. The blood is then transported into a culture bottle with a special culture medium. The bottle is then sent to the microbiology laboratory as soon as possible for further procedures. The causative organism for the kidney infection which has spread into the blood can be identified correctly if there is a positive colony count in the culture. But a negative culture test does not exclude because kidney infection can persist without spreading into the bloodstream.

In that case, sometimes multiple blood samples are taken for culture, at different times apart. ABST helps in starting the correctly sensitive antibiotic for the kidney infection causative organism. Because sometimes the organisms can be resistant to commonly used antibiotics. Co-amoxiclav is the most commonly used antibiotic in kidney infection and in resistant cases, antibiotics like ceftazidime and amikacin are used.

[ReadKidney Diagnostic Tests]

C-Reactive Proteins (CRP)

C-Reactive Proteins (CRP) is an inflammatory marker which is tested to aid the diagnosis of kidney infection. The blood is collected from a peripheral venous site, into a plain bottle. The test does not need the blood cells intact since the test needs only the serum.

Preparation and Procedure

No prior preparation is needed before drawing the blood. After collection, it should be transported the laboratory as soon as possible for further testing.

Results Interpretation

Elevated levels of CRP levels supports the diagnosis of ongoing acute inflammation. When there is a kidney infection it raises CRP levels as a response to the inflammation caused by it.

Erythrocyte Sedimentation Rate (ESR)

Erythrocyte Sedimentation Rate (ESR) is also a blood test for kidney infection identification. ESR is also an inflammatory marker in the human body which raises during both acute and chronic inflammation.

Preparation and Procedure

Blood collection does not need any special preparation. Blood is drawn from a peripheral vein and collected into a bottle with sodium citrate in 1:9 ratio.

Results Interpretation

Elevated ESR report, tells the clinician that the patient is having ongoing inflammation, and it can be due to the kidney infection.

Kidney Function Test

Lastly, kidney function test can be discussed as an important blood test performed in kidney infection. Kidney function test includes serum creatinine and blood urea levels.

Preparation and Procedure

As in most of the above investigations, this also does not require preparation. Blood is drawn and collected into a plain bottle since serum is adequate for the testing. A blood sample is sent to the laboratory as soon as possible. When there is an infection in the kidney, renal tubules which is a part of the functional unit of the kidney can get damaged. This can cause acute kidney injury and lead to acute renal failure. In acute renal failure serum creatinine will be elevated more than 50% from the baseline level and markedly elevated blood urea. In most cases, this injury is reversible and only symptomatic management is required.


Urine full report, urine culture, and ABST, USS-Kidney, ureter, bladder are some other important investigations that are performed to diagnose kidney infection. In this article, we focussed only on blood investigations. When a patient is suspected to be having an infection in their kidney, the above-mentioned blood tests are performed along with non-blood investigations. As patients, it is good to have some knowledge about blood tests for kidney infection to seek medical help when they are not well, without hesitation.